Dissertations / Theses on the topic 'Galaxies: abundance'
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Hempel, Angela. "Classification and abundance of extremely red galaxies with R-J]= 5." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973946733.
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SAMUROVIC, SRDJAN. "DARK MATTER IN EARLY-TYPE GALAXIES WITH X-RAY HALOES. A SPECTROSCOPIC STUDY OF DYNAMICS AND ABUNDANCE INDICES." Doctoral thesis, Università degli studi di Trieste, 2004. http://thesis2.sba.units.it/store/handle/item/12724.
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Sakr, Ziad. "Cosmology beyond ΛCDM model in the light of cluster abundance tension." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30346.
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Le modèle ΛCDM permet de décrire avec une grande précision la plupart des présentes observations cosmologiques. Cependant, l'un de ses paramètres, σ 8, mesurant l'amplitude de fluctuations de la matière, présente une discordance entre sa valeur contrainte par le spectre de puissance angulaire du CMB de la mission Planck, les Cls, et celle déterminée à partir des amas SZ dans l'univers proche. Dans le présent travail on explore divers extensions du modèle ΛCDM comme origines possibles de cette anomalie. Pour tester les effets de ces extensions, nous avons effectué une analyse Monte Carlo on l'on compare les contraintes sur σ 8 à partir de ΛCDM avec celles résultantes de ces extensions, et ceci en utilisant principalement le spectre de puissance CMB seul ou combiné avec des comptages d'amas. Ces derniers sont basés sur différentes relations masse observables et couvrent différents redshift : des amas de rayons X dans l'univers local, des amas de la mission SZ Planck dans l'univers proche ou une estimation des amas détectés par leur richesse photométrique à partir du la future mission Euclid. Du fait qu'une mauvaise détermination de l'étalonnage de la masse des amas pourrait également être la raison de cette divergence, notre approche consistait, lorsqu'on combinait les deux sondes issues des amas et du CMB, à laisser le facteur d'étalonnage libre afin qu'il soit contraint comme les autres paramètres cosmologiques par les deux données. Dans le cas d'introduction de trois neutrinos massifs dégénérés, nous avons trouvé qu'ils n'ont aucun effet significatif sur la correction de l'écart entre les contraintes issues de comptage CMB et ceux issues des Xray ou SZ cluster. Nous avons ensuite permis à l'indice de croissance ƴ de varier. Nous trouvons une corrélation entre ƴ et le paramètre de calibration masse-observable des amas détectés par rayons X qui n'est pas affecté par la présence ou non des neutrinos massifs. [...]The ΛCDM model has proved successful in describing to a high precision most of nowadays cosmological observations. However, one of its parameters, σ 8, measuring the present matter amplitude fluctuations, constrained from CMB angular power spectrum, the Cls, was found by the Planck mission, in significant tension with value constrained by SZ galaxy cluster counts in the near universe. In the present work we investigate extensions to ΛCDM model as possible origins behind this discrepancy. To test these extensions, we performed a Monte Carlo analysis to compare constraints on σ 8 in ΛCDM with constraints under these extensions, using mainly CMB Cls combined with cluster counts sample. The later were based on different mass observables relations and covered different redshift ranges: X-ray cluster in the local universe, SZ Planck mission clusters from the near universe or photometric richness estimated detected clusters from future high redshift upcoming Euclid alike mission. Because an improper determination of the calibration of cluster mass function could also be behind this discrepancy, our approach was, when combined with CMB, to leave the calibration factor free to vary and be constrained by data. Introducing three degenerate massive neutrinos, we found that they have no significant effect on fixing the discrepancy between CMB and Xray or SZ cluster counts. We then allowed the growth index ƴ to vary. We find a correlation in the confidence space between ƴ and the X-ray mass observable factor not affected by the presence of massive neutrinos, indicating that a modifying gravity is favored over massive neutrinos as a way to alleviate the tension. However, when a SZ cluster sample covering a larger redshift range was used, we found that the correlation between ƴ and the calibration factor, is constrained by the evolution of the growth through redshift and limited to a region where it cannot fix the discrepancy. [...]
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Diaz, Beltran A. I. "Chemical abundances in spiral galaxies." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372064.
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Guo, Yicheng, David C. Koo, Yu Lu, John C. Forbes, Marc Rafelski, Jonathan R. Trump, Ricardo Amorín, et al. "STELLAR MASS–GAS-PHASE METALLICITY RELATION AT 0.5 ≤ z ≤ 0.7: A POWER LAW WITH INCREASING SCATTER TOWARD THE LOW-MASS REGIME." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621237.
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We present the stellar mass (M-*)-gas-phase metallicity relation (MZR) and its scatter at intermediate redshifts (0.5 <= z <= 0.7) for 1381 field galaxies collected from deep spectroscopic surveys. The star formation rate (SFR) and color at a given M-* of this magnitude-limited (R less than or similar to 24 AB) sample are representative of normal star-forming galaxies. For masses below 10(9) M-circle dot, our sample of 237 galaxies is similar to 10 times larger than those in previous studies beyond the local universe. This huge gain in sample size enables superior constraints on the MZR and its scatter in the low-mass regime. We find a power-law MZR at 10(8) M-circle dot < M-* < 10(11) M-circle dot: 12 + log (O/H) = (5.83 +/- 0.19)+(0.30 +/- 0.02) log (M-*/M-circle dot). At 10(9) M-circle dot < M-* < 10(10.5) M-circle dot, our MZR shows agreement with others measured at similar redshifts in the literature. Our power-law slope is, however, shallower than the extrapolation of the MZRs of others to masses below 10(9) M-circle dot. The SFR dependence of the MZR in our sample is weaker than that found for local galaxies (known as the fundamental metallicity relation). Compared to a variety of theoretical models, the slope of our MZR for low-mass galaxies agrees well with predictions incorporating supernova energy-driven winds. Being robust against currently uncertain metallicity calibrations, the scatter of the MZR serves as a powerful diagnostic of the stochastic history of gas accretion, gas recycling, and star formation of low-mass galaxies. Our major result is that the scatter of our MZR increases as M-* decreases. Our result implies that either the scatter of the baryonic accretion rate (sigma((M) over dot)) or the scatter of the M-*-M-halo relation (sigma(SHMR)) increases as M-* decreases. Moreover, our measure of scatter at z = 0.7 appears consistent with that found for local galaxies. This lack of redshift evolution constrains models of galaxy evolution to have both sigma((M) over dot) and sigma(SHMR) remain unchanged from z = 0.7 to z = 0.
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Lipman, Keith. "Chemical abundances of primeval galaxies from QSO absorption lines." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363292.
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Van, der Swaelmen Mathieu. "Évolution chimique du Grand Nuage de Magellan." Phd thesis, Université Nice Sophia Antipolis, 2013. http://tel.archives-ouvertes.fr/tel-00833887.
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Malgré des années de travaux théoriques et observationnels intensifs, nous sommes toujours loin d'une complète compréhension de l'univers proche, la Voie Lactée (MW) et ses galaxies voisines. Parmi les satellites de la MW, le Petit et le Grand Nuage de Magellan (LMC) sont particulièrement intéressants puisqu'ils forment le plus proche exemple de galaxies en interaction gravitationnelle et hydrodynamique, et partant, constituent un laboratoire unique pour étudier les effets des marées et l'échange de matière sur l'évolution chimique et l'histoire de la formation stellaire d'une galaxie. Le LMC est une galaxie de petite masse barrée à disque, prototype des galaxies riches en gaz que l'on pense jouer un rôle important dans la construction des grandes galaxies dans le cadre du ΛCDM. De plus, avec sa métallicité actuelle d'environ le tiers de la métallicité solaire, le chemin d'enrichissement chimique suivi par le LMC donne un grand poids aux yields des générations stellaires pauvres en métaux, ce qui fait du LMC un environnement idéal pour étudier la nucléosynthèse aux basses métallicités. Ce travail de doctorat vise à: 1) caractériser chimiquement la population de la barre du LMC, 2) comparer les tendances des éléments de la MW et du LMC et interpréter les différences ou ressemblance en termes d'évolution chimique et/ou de processus nucléosynthétiques (contraintes sur les sites et les processus nucléosynthétiques), 3) comparer l'évolution chimique de la barre et du disque interne du LMC et interpréter les différence ou ressemblance dans le contexte de la formation de la barre. Nos résultats montrent que l'histoire chimique du LMC a connu un forte contribution des supernovae de type I ainsi qu'un fort enrichissement en éléments s par les vents d'étoiles AGB pauvres en métaux. Par rapport à la MW, les étoiles massives ont eu une contribution plus petite à l'enrichissement chimique du LMC. Les différences observées entre la barre et le disque parlent en faveur d'un épisode de formation stellaire accrue il y a quelques Gyr, ayant lieu dans les zones centrales du LMC et conduisant à la formation de la barre. Ceci est en accord avec les histoires de la formation stellaire récemment dérivées.
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Jeon, Myoungwon, Gurtina Besla, and Volker Bromm. "Connecting the First Galaxies with Ultrafaint Dwarfs in the Local Group: Chemical Signatures of Population III Stars." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/627108.
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We investigate the star formation history (SFH) and chemical evolution of isolated analogs of Local Group (LG) ultrafaint dwarf galaxies (UFDs; stellar mass range of 10(2)M(circle dot) < M-*< 10(5) M-circle dot) and gas-rich, low-mass dwarfs (Leo P analogs; stellar mass range of 10(5)M(circle dot) < M-*< 10(6) M-circle dot). We perform a suite of cosmological hydrodynamic zoom-in simulations to follow their evolution from the era of the first generation of stars down to z=0. We confirm that reionization, combined with supernova (SN) feedback, is primarily responsible for the truncated star formation in UFDs. Specifically, halos with a virial mass of M-vir less than or similar to 2 x 10(9) M-circle dot form greater than or similar to 90% of stars prior to reionization. Our work further demonstrates the importance of Population. III stars, with their intrinsically high [C/Fe] yields and the associated external metal enrichment, in producing low-metallicity stars ([Fe/H] less than or similar to -4) and carbon-enhanced metal-poor (CEMP) stars. We find that UFDs are composite systems, assembled from multiple progenitor halos, some of which hosted only Population. II stars formed in environments externally enriched by SNe in neighboring halos, naturally producing extremely low metallicity Population II stars. We illustrate how the simulated chemical enrichment may be used to constrain the SFHs of true observed UFDs. We find that Leo P analogs can form in halos with M-vir similar to 4 x 10(9) M-circle dot 9 (z = 0). Such systems are less affected byreionization and continue to form stars until z = 0, causing higher-metallicity tails. Finally, we predict the existence of extremely low metallicity stars in LG UFD galaxies that preserve the pure chemical signatures of Population III nucleosynthesis.
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Spencer, Meghin E., Mario Mateo, Matthew G. Walker, and Edward W. Olszewski. "A Multi-epoch Kinematic Study of the Remote Dwarf Spheroidal Galaxy Leo II." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623237.
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We conducted a large spectroscopic survey of 336 red giants in the direction of the Leo II dwarf galaxy using Hectochelle on the Multiple Mirror Telescope, and we conclude that 175 of them are members based on their radial velocities and surface gravities. Of this set, 40 stars have never before been observed spectroscopically. The systemic velocity of the dwarf is 78.3 +/- 0.6 km s(-1) with a velocity dispersion of 7.4 +/- 0.4 km s(-1). We identify one star beyond the tidal radius of Leo II but find no signatures of uniform rotation, kinematic asymmetries, or streams. The stars show a strong metallicity gradient of -1.53 +/- 0.10 dex kpc(-1) and have a mean metallicity of -1.70 +/- 0.02 dex. There is also evidence of two different chemodynamic populations, but the signal is weak. A larger sample of stars would be necessary to verify this feature.
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Tinker, Jeremy L., Joel R. Brownstein, Hong Guo, Alexie Leauthaud, Claudia Maraston, Karen Masters, Antonio D. Montero-Dorta, et al. "The Correlation between Halo Mass and Stellar Mass for the Most Massive Galaxies in the Universe." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624043.
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We present measurements of the clustering of galaxies as a function of their stellar mass in the Baryon Oscillation Spectroscopic Survey. We compare the clustering of samples using 12 different methods for estimating stellar mass, isolating the method that has the smallest scatter at fixed halo mass. In this test, the stellar mass estimate with the smallest errors yields the highest amplitude of clustering at fixed number density. We find that the PCA stellar masses of Chen et al. clearly have the tightest correlation with halo mass. The PCA masses use the full galaxy spectrum, differentiating them from other estimates that only use optical photometric information. Using the PCA masses, we measure the large-scale bias as a function of M-* for galaxies with logM(*) >= 11.4, correcting for incompleteness at the low-mass end of our measurements. Using the abundance matching ansatz to connect dark matter halo mass to stellar mass, we construct theoretical models of b(M-*) that match the same stellar mass function but have different amounts of scatter in stellar mass at fixed halo mass, sigma(logM*). Using this approach, we find sigma(logM*) = 0.18(+0.01) (-0.02). This value includes both intrinsic scatter as well as random errors in the stellar masses. To partially remove the latter, we use repeated spectra to estimate statistical errors on the stellar masses, yielding an upper limit to the intrinsic scatter of 0.16 dex.
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Vidal-García, A., S. Charlot, G. Bruzual, and I. Hubeny. "Modelling ultraviolet-line diagnostics of stars, the ionized and the neutral interstellar medium in star-forming galaxies." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/625298.
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We combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. We start by assessing the reliability of our stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large Magellanic Cloud clusters. In doing so, we find that neglecting stochastic sampling of the stellar initial mass function in these young (similar to 10-100 Myr), low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, we proceed and develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. Our model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. We use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. We find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. We also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM.
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Zahedy, Fakhri S., Hsiao-Wen Chen, Michael Rauch, and Ann Zabludoff. "HST Detection of Extended Neutral Hydrogen in a Massive Elliptical at z = 0.4." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625809.
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We report the first detection of extended neutral hydrogen (H I) gas in the interstellar medium (ISM) of a massive elliptical galaxy beyond z similar to 0. The observations utilize the doubly lensed images of QSO HE 0047-1756 at z(QSO) = 1.676 as absorption-line probes of the ISM in the massive (M-star approximate to 10(11) M-circle dot) elliptical lens at z = 0.408, detecting gas at projected distances of d = 3.3 and 4.6 kpc on opposite sides of the lens. Using the Space Telescope Imaging Spectrograph, we obtain UV absorption spectra of the lensed QSO and identify a prominent flux discontinuity and associated absorption features matching the Lyman series transitions at z = 0.408 in both sightlines. The H I column density is log N(H I)= 19.6-19.7 at both locations across the lens, comparable to what is seen in 21 cm images of nearby ellipticals. The H I gas kinematics are well-matched with the kinematics of the Fe II absorption complex revealed in ground-based echelle data, displaying a large velocity shear of approximate to 360 km s(-1) across the galaxy. We estimate an ISM Fe abundance of 0.3-0.4 solar at both locations. Including likely dust depletions increases the estimated Fe abundances to solar or supersolar, similar to those of the hot ISM and stars of nearby ellipticals. Assuming 100% covering fraction of this Fe-enriched gas, we infer a total Fe mass of M-cool(Fe) similar to (5-8) x 10(4) M-circle dot in the cool ISM of the massive elliptical lens, which is no more than 5% of the total Fe mass observed in the hot ISM.
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van, Haaften Lennart M., Thomas J. Maccarone, Paul H. Sell, J. Christopher Mihos, David J. Sand, Arunav Kundu, and Stephen E. Zepf. "An Excess of Low-mass X-Ray Binaries in the Outer Halo of NGC 4472." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/626536.
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We present new Chandra observations of the outer halo of the giant elliptical galaxy NGC 4472 (M49) in the Virgo Cluster. The data extend to 130 kpc (28'), and have a combined exposure time of 150 ks. After identifying optical counterparts using the Next Generation Virgo Cluster Survey to remove background active galactic nuclei and globular cluster (GC) sources, and correcting for completeness, we find that the number of field low-mass X-ray binaries (LMXBs) per unit stellar V-band light increases significantly with the galactocentric radius. Because the flux limit of the complete sample corresponds to the Eddington limit for neutron stars in NGC 4472, many of the similar to 90 field LMXBs in this sample could host black holes. The excess of field LMXBs at large galactocentric radii may be partially caused by natal kicks on black holes and neutron stars in binary systems in the inner part of the galaxy. Furthermore, because the metallicity in the halo of NGC 4472 strongly decreases toward larger galactocentric radii, the number of field LMXBs per unit stellar mass is anticorrelated with metallicity, opposite to what is observed in GCs. Another way to explain the spatial distribution of field LMXBs is therefore a reversed metallicity effect, although we have not identified a mechanism to explain this in terms of stellar and binary evolution.
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Rosales, Ortega Fernando Fabián. "Multi-dimensional analysis of the chemical and physical properties of spiral galaxies." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/224843.
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The PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey: PINGS, a 2-dimensional spectroscopic mosaicking of 17 nearby disk galaxies in the optical wavelength range. This project represents the first attempt to obtain continuous coverage spectra of the whole surface of a galaxy in the nearby universe. The final data set comprises more than 50000 individual spectra, covering in total an observed area of nearly 80 arcmin square. The powerful capabilities of wide-field 2D spectroscopic studies areproven. The chemical composition of the whole surface of a spiral galaxy ischaracterised for the first time as a function not only of radius, but of theintrinsic morphology of the galaxy, allowing a more realistic determination oftheir physical properties. The methodology, analysis and results of thisdissertation will hopefully contribute in a significant way to understand thenature of the physical and chemical properties of the gas phase in spiralgalaxies.
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Constantin, Anca. "Linking the Power Sources of Emission-Line Galaxy Nuclei from the Highest to the Lowest Redshifts." Ohio University / OhioLINK, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1097611827.
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Saro, A., S. Bocquet, J. Mohr, E. Rozo, B. A. Benson, S. Dodelson, E. S. Rykoff, et al. "Optical-SZE scaling relations for DES optically selected clusters within the SPT-SZ Survey." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/624426.
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We study the Sunyaev-Zel'dovich effect (SZE) signature in South Pole Telescope (SPT) data for an ensemble of 719 optically identified galaxy clusters selected from 124.6 deg(2) of the Dark Energy Survey (DES) science verification data, detecting a clear stacked SZE signal down to richness lambda similar to 20. The SZE signature is measured using matched-filtered maps of the 2500 deg(2) SPT-SZ survey at the positions of the DES clusters, and the degeneracy between SZE observable and matched-filter size is broken by adopting as priors SZE and optical mass-observable relations that are either calibrated using SPT-selected clusters or through the Arnaud et al. (A10) X-ray analysis. We measure the SPT signal-to-noise zeta - lambda relation and two integrated Compton-y Y500-lambda relations for the DES-selected clusters and compare these to model expectations that account for the SZE-optical centre offset distribution. For clusters with lambda > 80, the two SPT-calibrated scaling relations are consistent with the measurements, while for the A10-calibrated relation the measured SZE signal is smaller by a factor of 0.61 +/- 0.12 compared to the prediction. For clusters at 20 < lambda < 80, the measured SZE signal is smaller by a factor of similar to 0.20-0.80 (between 2.3 sigma and 10 sigma significance) compared to the prediction, with the SPT-calibrated scaling relations and larger lambda clusters showing generally better agreement. We quantify the required corrections to achieve consistency, showing that there is a richness-dependent bias that can be explained by some combination of (1) contamination of the observables and (2) biases in the estimated halo masses. We also discuss particular physical effects associated with these biases, such as contamination of. from line-of-sight projections or of the SZE observables from point sources, larger offsets in the SZE-optical centring or larger intrinsic scatter in the lambda-mass relation at lower richnesses.
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Belfiore, Francesco M. C. "Star formation, quenching and chemical enrichment in local galaxies from integral field spectroscopy." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/266684.
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Within the currently well-established ΛCDM cosmological framework we still lack a satisfactory un- derstanding of the processes that trigger, regulate and eventually quench star formation on galactic scales. Gas flows (including inflows from the cosmic web and supernovae-driven outflows) are con- sidered to act as self-regulatory mechanisms, generating the scaling relations between stellar mass, star formation rate and metallicity observed in the local Universe by large spectroscopic surveys. These surveys, however, have so far been limited by the availability of only one spectrum per galaxy. The aim of this dissertation is to expand the study of star formation and chemical abundances to resolved scales within galaxies by using integral field spectroscopy (IFS) data, mostly from the ongoing SDSS- IV MaNGA survey. In the first part of this thesis I demonstrate the ubiquitous presence of extended low ionisation emission-line regions (LIERs) in both late- and early-type galaxies. By studying the Hα equivalent width and diagnostic line ratios radial profiles, together with tracers of the underlying stellar popula- tion, I show that LIERs are not due to a central point source but to hot evolved (post-asymptotic giant branch) stars. In light of this, I suggest a new classification scheme for galaxies based on their line emission. By analysing the colours, star formation rates, morphologies, gas and stellar kinematics and environmental properties of galaxies with substantial LIER emission, I identify two distinct popula- tions. Galaxies where the central regions are LIER-like, but show star formation at larger radii are late types in which star formation is slowly quenched inside-out. This transformation is associated with massive bulges. Galaxies dominated by LIER emission at all radii, on the other hand, are red-sequence galaxies harbouring a residual cold gas component, acquired mostly via external accretion. Quiescent galaxies devoid of line emission reside in denser environments, which suggests environmental effects as a likely cause for the existence of line-less galaxies on the red sequence. In the second part of this dissertation I focus on the study of resolved chemical abundances by characterising the gas phase oxygen and nitrogen abundance gradients in a large sample of star forming galaxies. I analyse the deviations from an exponential profile at small and large radii and the dependence of the gradients on stellar mass. These findings are interpreted in the context of the inside-out paradigm of disc growth. I then demonstrate the necessity of gas flows, which are responsible for the observed flattening of the metallicity and N/O ratio gradients at large radii. Finally, I present a case study based on one nearby galaxy (NGC 628), in which I combine IFS and cold gas data to derive a spatially resolved metal budget and estimate the mass of metals lost by the galaxy throughout its life- time. By using simple physically-motivated models of chemical evolution I infer the average outflow loading factor to be of order unity.
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Fields, Dale L. "Absorption-line measurements of AGN outflows." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1155913695.
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Gutkin, Julia. "Constraints on the physical properties and chemical evolution of star-forming gas in primeval galaxies." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066255/document.
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Je présente un nouveau modèle d'émission nébulaire de galaxies à formation d'étoiles, que j'ai développé en combinant un modèle récent de synthèse de populations stellaires avec un code classique de photoionisation. Je détaille les principales caractéristiques de ce nouveau modèle, comme le traitement sophistiqué des abondances individuelles et des déplétions sur les grains de poussière qui permet d'explorer de façon appropriée les signatures des rapports non solaires d'abondances de métaux, et donc les propriétés des galaxies chimiquement jeunes à l'époque de la réionisation. Je présente la grille exhaustive publique de modèles de photoionisation que j'ai créée, explorant de larges éventails de paramètres stellaires et interstellaires. Je décris la capacité des modèles à reproduire simultanément les caractéristiques observationnelles de galaxies à formation d'étoiles dans plusieurs diagrammes de rapports de raies ultraviolettes et optiques, et j'explore l'influence des différents paramètres ajustables des modèles sur les prédictions de rapports de luminosités de raies. Je décris également comment la combinaison de ces modèles avec des modèles de régions d'émission de raies étroites autour de noyaux actifs de galaxies, effectués avec le même code de photoionisation, permet de définir de nouveaux diagnostics de rapports de raies d'émission ultraviolettes et optiques pour distinguer la formation stellaire et l'activité nucléaire dans les galaxies. Enfin, je montre comment le nouveau modèle présenté dans cette thèse a déjà été utilisé pour interpréter avec succès les raies d'émission ultraviolettes et optiques de galaxies naines lentillées à des décalages spectraux entre 2-7I present a new model of nebular emission from star-forming galaxies, which I have developed by combining updated stellar population synthesis models with a standard photoionization code. I detail the main features of this new model, such as the recent advances in the theories of stellar interiors and atmospheres it incorporates to interpret the ionizing radiation from star-forming galaxies, and the careful treatment of individual abundances and depletion onto dust grains, which allows one to properly explore the signatures of non-solar metal abundance ratios, and then the properties of chemically young galaxies out to the reionization epoch. I present the public comprehensive grid of photoionization models I have computed, including full ranges of stellar and interstellar parameters. I describe the ability of the models to account simultaneously for observational trends followed by star-forming galaxies in several ultraviolet and optical diagnostic line-ratio diagrams, and I explore the influence of the various adjustable model parameters on predicted line-luminosity ratios. I also describe how the combination of this model with calculations of narrow-line emitting regions from active galactic nuclei computed using the same photoionization code allows one to define new ultraviolet and optical emission-line diagnostics to discriminate between star formation and nuclear activity in galaxies. Finally, I show how the new model presented in this thesis has already been used successfully to interpret the rest-frame ultraviolet and optical line emission of different types of high-redshift star-forming galaxies, mainly lensed dwarf star-forming galaxies at redshift between 2-7
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Ballero, Silvia Kuna. "Evolution of chemical abundances in active and quiescent spiral bulges." Doctoral thesis, Università degli studi di Trieste, 2008. http://hdl.handle.net/10077/2560.
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2006/2007In this thesis I develop a chemical evolution model which takes advantage of the most recent high-quality abundance observations in the Galactic bulge to put constraints on its formation and evolution and to obtain a baseline model for bulges in general. I adopt updated massive star nucleosynthesis and follow the evolution of several alpha-elements and Fe by varying the evolutionary parameters. The [alpha/Fe] ratios in the bulge are correctly predicted to be supersolar for a wide range in [Fe/H], and the stellar metallicity distribution is reproduced assuming a short formation timescale, a high star formation efficiency and an initial mass function flatter than the disk. Metallicity-dependent oxygen yields with stellar mass loss are included in the chemical evolution models for the bulge and the solar neighbourhood. The agreement between predicted and observed [O/Mg] trends above solar metallicity is significantly improved; a normalisation problem probably indicates that the adopted semi-empirical yields need adjustment. The difference between [O/Fe] and the other [alpha/Fe] ratios in the bulge and solar neighbourhood is explained. I test the so-called universal initial mass function, suitable for ellipticals and disks, to see if the bulge stellar metallicity distribution can be reproduced by varying the yields for very massive stars, and included M31 in my analysis. I show that assuming a flatter initial mass function than the universal one is necessary, and that a variation exists in the initial mass function among different environments. Finally, I investigate the evolution of spiral bulges hosting Seyfert nuclei, with detailed calculations of the galactic potential and of the feedback from the central supermassive black hole in an Eddington-limited accretion regime. New spectro-photometrical evolution codes covering a wide range of stellar ages and metallicities allowed to model the photometric features of local bulges. I successfully predict the observed black hole-host bulge mass relation. The observed present-day nuclear bolometric luminosity is achieved only for the most massive bulges, otherwise a rejuvenation is necessary. The observed high star formation rates and metallicities, constancy of chemical abundances with the redshift and bulge present-day colours are reproduced, but a steeper initial mass function is required to match the colour-magnitude relation and the present K-band bulge luminosity.
In questa tesi, ho sviluppato un modello di evoluzione chimica che si avvale di recenti osservazioni ad alta qualità di abbondanze chimiche nel bulbo della Via Lattea, per porre dei vincoli sui suoi meccanismi di formazione ed evoluzione e ottenere un modello generale per i bulbi di spirale. Ho adottato una nucleosintesi aggiornata per le stelle massicce e seguito l'evoluzione di diversi elementi-alpha e del ferro, variando i parametri evolutivi. Si prevede correttamente che i rapporti [alpha/Fe] nel bulbo siano soprasolari per un ampio intervallo in [Fe/H]. La distribuzione in metallicità è riprodotta con un tempo di formazione breve, un'alta efficienza di formazione stellare e una funzione iniziale di massa più piatta che nel disco. Yields di ossigeno con perdita di massa stellare in funzione della metallicità sono stati inclusi nei modelli di evoluzione chimica del bulbo e dei dintorni solari. L'accordo tra gli andamenti di [O/Mg] previsti e osservati per metallicità soprasolari risulta sensibilmente migliorato; si spiega inoltre la differenza tra il rapporto [O/Fe] e gli altri [alpha/Fe] nel bulbo e nei dintorni solari. Un problema di normalizzazione indica che probabilmente gli yields semi-empirici adottati necessitano una revisione. Ho verificato se con la cosiddetta funzione iniziale di massa universale, adeguata per galassie ellittiche e dischi, la distribuzione in metallicità stellare del bulge può essere riprodotta calibrando gli yields delle stelle supermassicce, includendo M31 nell'analisi. Si dimostra che una funzione iniziale di massa più piatta di quella universale è necessaria, e che esiste una variazione nella funzione iniziale di massa tra i diversi ambienti. Infine, ho studiato l'evoluzione di bulbi di spirali che ospitano galassie di Seyfert, mediante calcoli dettagliati del potenziale galattico e del feedback dal buco nero supermassiccio centrale in un regime di accrescimento limitato dal tasso di Eddington. Nuovi codici spettro-fotometrici che coprono un ampio intervallo di età stellari e di metallicità hanno permesso di modellizzare le caratteristiche fotometriche dei bulbi locali. La relazione osservata tra massa del buco nero e del bulbo ospite è prevista con successo. La luminosità bolometrica nucleare misurata al tempo presente si consegue solo per i bulbi più massicci, negli altri casi è necessario un "ringiovanimento". Le osservazioni di alto tasso di formazione stellare, alte metallicità, invarianza di abbondanze chimiche col redshift e colori dei bulbi locali sono riprodotte; una funzione iniziale di massa più ripida è invece richiesta per la relazione colore-magnitudo e la luminosità dei bulbi in banda K al tempo presente.
XX Ciclo
1979
21
Rémy-Ruyer, Aurélie. "Probing the impact of metallicity on the dust properties in galaxies." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112340/document.
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Alors que les galaxies évoluent, leur milieu interstellaire (MIS) s’enrichit continuellement en métaux, et cet enrichissement influence la formation d’étoiles. Les galaxies naines de faible métallicité de l’Univers Local sont les candidates idéales pour étudier l’influence de cet enrichissement en métaux sur les propriétés du MIS des galaxies et nous donne un aperçu des processus d’enrichissement et de formation stellaire dans des conditions proches de celles trouvées dans les systèmes pauvres en métaux de l’Univers primordial. Des études précédentes ont montré que le MIS des galaxies naines pose un certain nombre d’énigmes en terme d’abondance des grains, de composition de la poussière et même des processus d’émission en infrarouge lointain (FIR). Cependant, ces études étaient limitées à la poussière chaude émettant à des longueurs d’onde plus courtes que 200 micromètres et étaient effectuées sur un petit nombre de galaxies. Grâce à une sensibilité et une résolution améliorées dans les domaines FIR et submillimétriques (submm), Herschel nous donne une vue nouvelle sur les propriétés de la poussière froide dans les galaxies et nous permet d’étudier les galaxies les plus pauvres en métaux de manière systématique. Dans ce travail, je mène une étude des propriétés des poussières dans les galaxies naines et compare avec des environnements plus riches en métaux, pour aborder la question de l’impact de la métallicité sur les propriétés de la poussière. La nouveauté de ce travail réside dans le fait que les galaxies naines sont étudiées de manière systématique, nous permettant d’accéder aux, et de quantifier les propriétés générales représentatives de ces systèmes. Cette étude est conduite sur toute la gamme de longueurs d’onde infrarouge (IR)-submm, avec les nouvelles observations en FIR/submm d’Herschel, ainsi que des données Spitzer, WISE, IRAS, et 2MASS. Nous complétons ces données avec des mesures en domaine submm de télescopes au sol comme APEX ou le JCMT, pour étudier la présence et les caractéristiques de l’excès submm dans mon échantillon de galaxies. Je collecte aussi les données HI et CO pour accéder aux propriétés du gaz dans ces galaxies et étudier l’évolution du rapport en masse gaz-sur-poussière (G/D) avec la métallicité. Notre étude révèle des propriétés de poussière différentes dans les environnements de faible métallicité que celles observées dans des systèmes plus riches en métaux (par exemple, une poussière globalement plus chaude). Une émission en excès par rapport aux modèles utilisés, apparait souvent aux alentours de 500 micromètres, menant à d’importantes incertitudes sur les propriétés de la poussière, notamment sur la masse de poussière. Les excès les moins importants peuvent cependant être expliqués en utilisant une autre composition pour la poussière, avec des grains plus émissifs. Traceur idéal de l’état d’évolution chimique d’une galaxie, le G/D est en fait bien plus grand que ce que l’on pourrait attendre si l’on considère un modèle simple d’évolution chimique. Interprétée avec des modèles d’évolution chimique plus complexes, incorporant des processus de croissance des grains et/ou une formation d’étoiles épisodique, la relation entre le G/D et la métallicité, ainsi que sa dispersion, peuvent être expliquées par la grande variété d’environnements que nous considérons dans notre étudeAs galaxies evolve, their Interstellar Medium (ISM) becomes continually enriched with metals, and this metal enrichment influences the subsequent star formation. Low metallicity dwarf galaxies of the local Universe are ideal candidates to study the influence of metal enrichment on the ISM properties of galaxies and gives us insight into the enrichment process and star formation under ISM conditions that may provide clues to conditions in early universe metal-poor systems. Previous studies have shown that the ISM of dwarf galaxies poses a number of interesting puzzles in terms of the abundance of dust grains, the dust composition and even the FIR emission processes. However these studies were limited to the warmer dust emitting at wavelengths shorter than 200 microns and were done only on a small number of dwarf galaxies. Thanks to its increased sensitivity and resolution in FIR and submillimeter (submm) wavelengths, Herschel gives us a new view on the cold dust properties in galaxies and enables us to study the lowest metallicity galaxies in a systematic way. In this work, I carry out a study of the dust properties in dwarf galaxies and compare with more metal rich environments, in order to address the question of the impact of metallicity on the dust properties. The novelty of this work lays in the fact that dwarf galaxies are studied here in a systematic way, enabling us to derive and quantify the general properties that are representative of these systems. This study is conducted over the full IR-to-submm range, using new FIR/submm Herschel observations, Spitzer, WISE, IRAS and 2MASS data. We complete this set of data with longer submm measurements from ground-based facilities such as APEX and JCMT to study the presence and characteristics of the submm excess in my sample of galaxies. I also collect Hi and CO data to access the gas properties of the galaxies and study the evolution of the G/D with metallicity. Our study reveal different dust properties in low-metallicity environments than that observed in more metal-richs systems (e.g., an overall warmer dust component). An excess submm emission is often apparent near and/or beyond 500 microns rendering large uncertainties in the dust properties, even for something as fundamental as dust masses. Some of the smallest excesses can be explained by using another dust composition with more emissive grains. Ideal tracer of the chemical evolutionary stage of a galaxy, the gas-to-dust mass ratios (G/D) is found to be much higher than what is expected by simple chemical evolution models. Interpreted with more sophisticated chemical evolution models, including dust growth in the ISM and/or episodic star formation, the relation of the G/D with metallicity and its scatter can be explained by the wide variety of environments we are considering
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Spitoni, Emanuele. "The effects of galactic fountains on the chemical evolution of galaxies." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3435.
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2008/2009In this thesis we study the effect of galactic fountains, namely gas and flows from the disk of galaxies produced by multiple supernova explosions, on the chemical evolution of galaxies. Sequential supernova explosions create a superbubble, whereas the swept up interstellar medium is concentrated in a supershell which can break out a stratified medium, producing bipolar outflows. The gas of the supershells can fragment into clouds which eventually fall toward the disk producing so-called galactic fountains. Many works in literature have dealt with superbubble expansion in stratified media. However, very few papers in the past have taken into account the chemical evolution of the superbubble and how the supershell get polluted from the metals produced by supernova explosions. With this thesis for the first time the effect of galactic fountains we consider in a detailed chemical evolution model for the Milky Way. In the first part of our work we study the expansion law and chemical enrichment of a supershell powered by the energetic feedback of a typical Galactic OB association at various galactocentric radii. We follow the orbits of the fragments created when the supershell breaks out and we compare their kinetic and chemical properties with the available observations of high - and intermediate - velocity clouds. We use the Kompaneets (1960) approximation for the evolution of the superbubble driven by sequential supernova explosions and we compute the abundances of oxygen and iron residing in the thin cold supershell. Due to Rayleigh-Taylor instabilities we assume that supershells are fragmented and we follow the orbit of the clouds either ballistically or by means of a hybrid model considering viscous interaction between the clouds and the extra-planar gas. We find that if the initial metallicity is solar, the pollution from the dying stars of the OB association has a negligible effect on the chemical composition of the clouds. The maximum height reached by the clouds above the plane seldom exceeds 2 kpc and when averaging over different throwing angles, the landing coordinate differs from the throwing coordinate by only 1 kpc. Therefore, it is unlikely that galactic fountains can affect abundance gradients on large scales. The range of heights and [O/Fe] ratios spanned by our clouds suggest that the high velocity clouds cannot have a Galactic origin, whereas intermediate velocity clouds have kinematic properties similar to our predicted clouds but have observed overabundances of the [O/Fe] ratios that can be reproduced only with initial metallicities which are too low compared to those of the Galaxy disk. Even if it is unlikely that galactic fountains can affect abundance gradients on large scales, they can still affect the chemical enrichment of the interstellar medium (ISM) because of the time-delay due to the non-negligible time taken by fountains to orbit around and fall back into the Galaxy. This implies a delay in the mixing of metals in ISM which conflicts with the instantaneous mixing approximation usually assumed in all models in literature. We test whether relaxing this approximation in a detailed chemical evolution model can improve or worsen the agreement with observations. To do that, we investigate two possible causes for relaxing of the instantaneous mixing: i) the ``galactic fountain time delay effect'' and ii) the ``metal cooling time delay effect''. We find that the effect of galactic fountains is negligible if an average time delay of 0.1 Gyr, as suggested by our model, is assumed. Longer time delays produce differences in the results but they are not realistic. The metal cooling time delays produce strong effects on the evolution of the chemical abundances only if we adopt stellar yields depending on metallicity. If, instead, the yields computed for the solar chemical composition are adopted, negligible effects are produced, as in the case of the galactic fountain delay. The relaxation of the IMA by means of the galactic fountain model, where the delay is considered only for massive stars and only in the disk, does not affect the chemical evolution results. The combination of metal dependent yields and time delay in the chemical enrichment from all stars starting from the halo phase, instead, produces results at variance with observations.
XXII Ciclo
1979
23
Trevisan, Marina. "Formação e evolução de galáxias: populações estelares na Via Láctea, galáxias elípticas e propriedades de galáxias em grupos." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-18042012-162353/.
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Entender como as galáxias se formam e evoluem ao longo do tempo é um dos maiores desafio da cosmologia moderna. Vários processos estão presentes na formação de galáxias, tais como o feedback de supernovas e núcleos galácticos ativos, evolução química e dinâmica, e também efeitos ambientais. Esta tese abrange estes processos, a partir de um ponto de vista observacional. A Via Láctea tem um papel fundamental na compreensão dos vários processos envolvidos na formação de uma galáxia, e começamos nosso projeto estudando nossa própria galáxia. Diferentes processos deixam assinaturas típicas na distribuição de velocidades e metalicidades das estrelas. Por esta razão, combinando cinemática e abundâncias químicas, foi possível determinar a origem de uma amostra de estrelas velhas e ricas em metais. Compreender como e onde essas estrelas se formaram está intimamente relacionado com mecanismos presentes na evolução do disco Galáctico. Apesar de não podermos observar estrelas individuais em galáxias distantes, somos capazes de inferir a história de formação destas galáxias combinando modelos de população estelar simples, de forma a reproduzir o espectro observado. Usando esta metodologia, foi possível traçar a história de formação estelar de galáxias elípticas, e dessa forma restringir os mecanismos de feedback que regulam a formação de estrelas em halos. No cenário Lambda-CDM, as estruturas menores são formadas primeiro, e então elas se agrupam, formando assim estruturas cada vez maiores. As galáxias, ao serem incorporadas à sistemas maiores, sofrem os efeitos de diversos processos que atuam em ambientes de alta densidade, mudando assim suas propriedades. Desta forma, a evolução das galáxias e a formação de estruturas em grande escala andam lado a lado, como mostramos em nosso estudo de propriedades de galáxias em grupos. Exploramos a distribuição espacial das galáxias na vizinhança de grupos, e também usamos a distribuição de velocidades das galáxias para determinar o estágio evolutivo do grupo. Foram encontradas correlações importantes entre o estágio evolutivo do grupo e as populações de galáxias que nestes residem.Understanding the way galaxies form and evolve throughout the cosmic time remains one of the greatest challenges of modern cosmology. Several processes are known to play a role in the formation of galaxies, such as feedback from supernovae and active galactic nuclei, chemical and dynamical evolution and environmental effects. This thesis encompasses these processes, from an observational point of view. The Milky Way plays a pivotal role in understanding the various processes involved in the formation of a galaxy, and we start our understanding program by studying our own Galaxy. Different formation processes leave typical signatures in the velocity and metallicity distribution of stars. For this reason, we were able to trace the origin of old and metal-rich stars by combining their kinematics and chemical abundances. Understanding how and where these stars were formed is closely related to mechanisms driving the evolution of the Galactic disk. Although we cannot observe individual stars in distant galaxies, only the integrated spectra, we are able to infer the mass assembly history of galaxies by combining single stellar population (SSP) models that reproduce the observed spectrum. Using this methodology, we traced the star formation history of elliptical galaxies and, by studying the signatures left in the star formation history, we were able to constrain the feedback mechanisms regulating the star formation within halos. In the LCDM scenario, small scale structures are formed first, and then they merge forming larger and larger structures. Therefore, galaxies grow into more and more massive systems, and processes operating in these high-density environments change their properties. For this reason, galaxy evolution and formation of large-scale structures go hand in hand, as we show in our study of properties of galaxies in groups. We explored the spatial distribution of galaxies within and in the surrounding of groups, and we also used the velocity distribution of galaxies as a probe of the evolutionary stage of the group. We found important correlations between the evolutionary stage of the group and the population of galaxies residing within it.
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Rojas-Arriagada, Álvaro. "Étude du bulbe galactique avec le Gaia-ESO survey." Thesis, Université Côte d'Azur (ComUE), 2016. http://www.theses.fr/2016AZUR4056/document.
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Le bulbe Galactique, est cruciale pour comprendre les processus physiques responsables de la formationde la galaxie. L'étude spectroscopique des étoiles vieilles de faible masse permettre de caractériser endétail la chimie et la cinématique du bulbe. Dans cette thèse, nous avons utilisé des données provenantdu Gaia-ESO survey pour mener une étude détaillée du système du disque ainsi que du bulbeGalactique. La distribution de métallicité du bulbe est bimodale. La population riche en métaux montreune cinématique typique de la barre. Elle présente une caractéristique de double RC et recouvre laséquence du disque mince à haute métallicité dans le plan [Mg/Fe] vs. [Fe/H]. Nous associons cesétoiles avec celles de la barre formée à la suite de l'évolution séculaire du disque mince primordial.D'autre part, la population pauvre en métaux présente une cinématique chaude et ne participe pas à laforme en X du bulbe. Ces étoiles semblent imiter la distribution de celles du disque épais dans le plan[Mg/Fe] vs. [Fe/H]. Quand nous comparons la position en métallicité du genou de cette distribution,qui se trouve à [Fe/H]=-0.37+/-0.09 dex, elle est plus élevée de 0.6 dex par rapport au disque épais. Unmodèle d'évolution chimique permet de bien ajuster cette distribution pour les étoiles du bulbe ensupposant un épisode de formation stellaire rapide (<1 Gyr) et intense. L'origine du bulbe pauvre enmétaux reste encore relativement incomprise, mais divers projets futurs devraient permettre de faire ladistinction entre les processus violents ou ceux liés à une évolution séculaire qui ont pu contribuer à saformationThe Galactic bulge, as a massive and old Galactic component, is key to understand the physicalprocesses responsibles for the formation of the Galaxy. The spectroscopic study of long lived low massstars represents an opportunity to characterize the detailed chemical and kinematical patterns of theeventual mix of stellar populations building up the bulge. In this thesis we made use of data comingfrom the Gaia-ESO survey to conduct a detailed analysis of the disk system as well as bulge stellarpopulations. The bulge metallicity distribution function is bimodal. The metal-rich population exhibitsbar-like kinematics, displays the double RC feature and overlaps the metal-rich end of the thin disksequence in the [Mg/Fe] vs. [Fe/H] plane. We associate these stars with the bar X-shape bulge formedas the product of secular evolution of the early thin disk. On the other hand, the metal-poor populationpresents isotropic hot kinematics and does not participate in the X-shaped bulge. When compared to thethick disk, bulge stars seem to mimic their distribution in the [Mg/Fe] vs. [Fe/H] plane. Whencomparing the metallicity position of the so called ``knee'', that of the bulge is found to be at [Fe/H]=-0.37+/-0.09 dex, being 0.6 dex higher than that of the thick disk. A chemical evolution model suitablyfits the whole bulge sequence by assuming a fast (<1 Gyr) intense burst of star formation taking place atearly epochs. The origin of the metal-poor bulge still remains unconstrained, but further research shouldallow to distinguish between violent processes or secular evolution for its origin
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Titarenko, Anastasia. "Indicateurs chimiques d’âge stellaire à l’ère de Gaia." Thesis, Université Côte d'Azur (ComUE), 2018. http://www.theses.fr/2018AZUR4065/document.
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Les étoiles enregistrent le passé dans leurs âges, leurs compositions chimiques et leur cinématique. Elles peuvent fournir des contraintes détaillées sur les premières époques de la formation des galaxies, jusqu’aux redshifts supérieurs à deux (un recul d’environ 10 milliards d’années). En particulier, les âges stellaires sont essentiels pour la compréhension de l’histoire de la Voie Lactée et pour la comparaison avec les modèles d’évolution galactique.L’avènement de la mission spatiale Gaia ouvre la voie à l’estimation de l’âge pour de grands échantillons d’étoiles. En particulier, les méthodes basées sur l’ajustement d’isochrones peuvent être utilisées. En plus, les distances précises mesurées par Gaia permettent de développer les estimateurs d’âge indirects basés sur l’horloge d’évolution de la population stellaire. En fait, les schémas d’abondance chimique, imprimés sur les atmosphères stellaires, représentent les conditions du gaz au moment de la formation des étoiles à des redshifts supérieurs à deux. Les produits d’évolution chimique de différents canaux nucléosynthétiques peuvent donc fournir une approximation temporelle, qui, après l’étalonnage, peut être utilisé comme un estimateur d’âge.Cette thèse est centrée sur l’utilisation d’horloge chimique particulière : l’abondance [Y/Mg]. À cette fin, les premières données astrométriques de la mission Gaia ont été combinées avec des données spectroscopiques à haute résolution du catalogue AMBRE HARPS. Tout d’abord, l’identification des objets d’AMBRE a été améliorée grâce à la correspondance avec le catalogue 2MASS et la Gaia DR1. Au total, 6776 étoiles ont été identifiées.Deuxièmement, afin d’obtenir des estimations précises du rapport d’abondance [Y/Mg] pour les étoiles du disque galactique, l’outil automatisé GAUGUIN, intégré à la chaîne Gaia DPAC APSIS, a été optimisé et testé. En particulier, les capacités d’estimation d’abondances chimiques ont été améliorées pour des grilles de spectres synthétiques irrégulières, couvrant une large gamme de paramètres atmosphériques stellaires.Troisièmement, le ratio [Y/Mg] a été estimé pour environ 2000 étoiles à partir des données spectroscopiques d’AMBRE HARPS. Les erreurs internes et externes des abondances ont été soigneusement analysées. Les étoiles étudiées appartiennent principalement aux disques mince et épais galactique, dans la gamme de métallicité allant de –1,0 dex à 0,5 dex.Quatrièmement, grâce à l’estimation d’âge basée sur l’adaptation des isochrones pour 342 "turn-off" étoiles d’échantillon, la sensibilité à l’âge du rapport [Y/Mg] a été étudié. L’analyse révèle une corrélation claire entre [Y/Mg] et l’âge pour les étoiles du disque mince de différentes métallicités. Cela correspond aux études antérieures sur les étoiles de type solaire. De plus, aucune dépendance à la métallicité avec l’âge stellaire n’est détectée, donc le ratio [Y/Mg] peut être utilisé comme un indicateur fiable d’âge. Enfin, la relation [Y/Mg] versus l’âge présente une discontinuité entre les étoiles du disque épais autour de 9–10 Gyrs. Pour ces étoiles, la corrélation est différente et a une tendance probablement plus forte avec l’âge. Cela reflète la différence dans les histoires d’évolution chimique pour les deux composantes du disqueStars record the past in their ages, chemical compositions and kinematics. They can provide unprecedented detailed constraints on the early epochs of galaxy formation, back to redshifts greater than two (a look-back time of around 10 billion years). In particular, stellar ages are crucial to the understanding of the Milky Way history and for comparison with galactic evolution models. The advent of the Gaia space mission has opened the path to stellar age estimations for large samples of stars, in particular, based on isochrone fitting methods. In addition, Gaia precise distances allow to develop indirect age estimations based on the stellar population chemical evolution clock. In fact, the chemical abundance patterns imprinted on stellar atmospheres represent the gas conditions at the time of the stars’ formation back to redshifts greater than two. The chemical evolution products of different nucleosynthetic channels can therefore provide a time proxy. After calibration, it can be used as an age estimator.This thesis is focussed on the use of a particular chemical clock, the [Y/Mg] abundance. To this purpose, the astrometric Gaia mission data from the first data release was combined with high resolution spectroscopic data from the AMBRE-HARPS catalogue. First of all, the object identification of the AMBRE archival data was improved, thanks to a cross match with the 2MASS catalog, and later the Gaia DR1. In total, 6776 different stars have been identified.Secondly, in order to obtain precise estimations of the [Y/Mg] abundance ratio for galactic disc stars, the automated GAUGUIN tool integrated in the Gaia DPAC APSIS chain, has been optimized and tested. In particular, the abundance estimation capabilities of the APSIS GAUGUIN tool have been improved for irregularly distributed synthetic spectra grids, spanning a large range in stellar atmospheric parameters.Thirdly, the [Y/Mg] abundance ratio has been estimated for about 2000 stars from the AMBRE HARPS spectroscopic data. In addition, the internal and external errors of the abundances were carefully analysed. The studied stars belong mainly to the galactic thin and thick disc, in the metallicity range from --1.0 dex to 0.5 dex.Fourth, thanks to the isochrone fitting age estimations of 342 turn-off stars of the sample, the age sensitivity of the [Y/Mg] ratio has been studied. The analysis reveals a clear correlation between [Y/Mg] and age for thin disk stars of different metallicities, in synergy with previous studies of Solar type stars. In addition, no metallicity dependence with stellar age is detected, allowing to use the [Y/Mg] ratio as a reliable age proxy.Finally, the [Y/Mg] vs. age relation presents a discontinuity between thin and thick disk stars around 9–10 Gyrs. For thick disk stars, the correlation has a different zero point and probably a steeper trend with age, reflecting the different chemical evolution histories of the two disk components
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Cesetti, Mary. "Observational constraints to the stellar populations in the center of galactic spheroids." Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426046.
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Galactic spheroids represent one of the key challenges to our understanding of galaxies formation and evolution as far as their star-formation history is concerned. The knowledge of the stellar content of early-type galaxies is fundamental to understand their star formation and chemical evolution. The thesis is focused on two main topics, both concerned with the study of unresolved stellar populations in the centers of galaxies. The first one is a comprehensive study of the photometrical properties of three galaxies that belong to the Virgo Cluster and host Nuclear Stellar Disks (NSD) in their centers. The second one is focused on the study of absorption lines in the Near-infrared (NIR) that are strictly correlated with the properties of the stellar populations. I defined new NIR spectral indices that show great potential for a stellar population analysis. A simple SSP model is created to interpret the integrated NIR light. The development of the SSPs model pointed out at some limitations of the currently available stellar spectral libraries. Consequently, the study of metal poor red supergiant stars in the NIR was carried out.Gli sferoidi galattici rappresentano uno dei punti chiave per comprendere la formazione e l'evoluzione delle galassie, sopratutto per quanto riguarda la formazione stellare. Infatti, conoscere il contenuto stellare delle galassie early-type fornishe importanti indicazioni sulla formazione e l'evoluzione chimica delle loro stelle. Due sono gli argomenti trattati in questa tesi entrambi connessi con lo studio delle popolazione stellari non risolte nel centro delle galassie. Il primo studia dettagliatamente le proprietà fotometriche di tre galassie appartenenti all'ammasso della Vergine che ospitano un disco stellare nel loro nucleo. Il secondo mira ad individuare le righe spettrali fondamentali per lo studio delle popolazioni stellari nel vicino infrarosso (NIR). I nuovi indici spettrali definiti nel NIR hanno dimostrato essere notevolmente efficaci per l'analisi delle popolazioni stellari. Un semplice modello di popolazione stellare semplice (SSP) è stato creato per interpretare la luce integrata nel vicino infrarosso. Lo sviluppo del modello SSP ha messo in evidenza alcuni limiti delle librerie stellari spettrali oggigiorno disponibili. Pertanto è stato studiato lo spettro di alcune stelle supergiganti rosse a bassa metallicità nel NIR.
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Boeche, Corrado. "Chemical gradients in the Milky Way from unsupervised chemical abundances measurements of the RAVE spectroscopic data set." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5247/.
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The present thesis was born and evolved within the RAdial Velocity Experiment (RAVE) with the goal of measuring chemical abundances from the RAVE spectra and exploit them to investigate the chemical gradients along the plane of the Galaxy to provide constraints on possible Galactic formation scenarios.
RAVE is a large spectroscopic survey which aims to observe spectroscopically ~10^6 stars by the end of 2012 and measures their radial velocities, atmospheric parameters and chemical abundances. The project makes use of the UK Schmidt telescope at Australian Astronomical Observatory (AAO) in Siding Spring, Australia, equipped with the multiobject spectrograph 6dF. To date, RAVE collected and measured more than 450,000 spectra. The precision of the chemical abundance estimations depends on the reliability of the atomic and atmosphere parameters adopted (in particular the oscillator strengths of the absorption lines and the effective temperature, gravity, and metallicity of the stars measured). Therefore we first identified 604 absorption lines in the RAVE wavelength range and refined their oscillator strengths with an inverse spectral analysis. Then, we improved the RAVE stellar parameters by modifying the RAVE pipeline and the spectral library the pipeline rely on. The modifications removed some systematic errors in stellar parameters discovered during this work. To obtain chemical abundances, we developed two different processing pipelines. Both of them perform chemical abundances measurements by assuming stellar atmospheres in Local Thermodynamic Equilibrium (LTE). The first one determines elements abundances from equivalent widths of absorption lines. Since this pipeline showed poor sensibility on abundances relative to iron, it has been superseded. The second one exploits the chi^2 minimization technique between observed and model spectra. Thanks to its precision, it has been adopted for the creation of the RAVE chemical catalogue. This pipeline provides abundances with uncertains of about ~0.2dex for spectra with signal-to-noise ratio S/N>40 and ~0.3dex for spectra with 20>S/N>40. For this work, the pipeline measured chemical abundances up to 7 elements for 217,358 RAVE stars.
With these data we investigated the chemical gradients along the Galactic radius of the Milky Way. We found that stars with low vertical velocities |W| (which stay close to the Galactic plane) show an iron abundance gradient in agreement with previous works (~-0.07$ dex kpc^-1) whereas stars with larger |W| which are able to reach larger heights above the Galactic plane, show progressively flatter gradients. The gradients of the other elements follow the same trend. This suggests that an efficient radial mixing acts in the Galaxy or that the thick disk formed from homogeneous interstellar matter. In particular, we found hundreds of stars which can be kinetically classified as thick disk stars exhibiting a chemical composition typical of the thin disk. A few stars of this kind have already been detected by other authors, and their origin is still not clear. One possibility is that they are thin disk stars kinematically heated, and then underwent an efficient radial mixing process which blurred (and so flattened) the gradient. Alternatively they may be a transition population" which represents an evolutionary bridge between thin and thick disk. Our analysis shows that the two explanations are not mutually exclusive. Future follow-up high resolution spectroscopic observations will clarify their role in the Galactic disk evolution.Die vorliegende Doktorarbeit wurde im Rahmen des RAdial Velocity Experiment (RAVE) angefertigt. Ihr Ziel ist es, chemische Elementhäufigkeiten an RAVE-Spektren zu messen und zur Untersuchung chemischer Gradienten in der Milchstrassenebene zu benutzen, um verschieden Szenarien der Galaxienentstehung einzugrenzen. RAVE ist eine große spektrokopische Durchmusterung, deren Ziel es ist, bis zum Ende des Jahres 2012 insgesamt 10^6 Sterne zu spektroskopieren, um deren Radialgeschwindigkeiten, sternatmosphärische Parameter und chemische Häufigkeiten zu messen. Das Projekt benutzt das UK Schmidt Teleskop am Australian Astronomical Observatory (AAO) in Siding Spring, Australien, welches mit dem Multiobjekt-Spektrographen 6dF bestückt ist. Bis heute hat RAVE die Spektren von mehr als 450,000 Sternen gesammelt und untersucht. Die Genauigkeit, mit der die Elementhäufigkeiten abgeschätzt werden können, hängt von der Zuverlässigkeit der verwendeten Parameter, (insbesondere der Oszillatorstärken der Absorptionslinien sowie von der effektiven Temperatur, Schwerebeschleunigung und der Metallizität des gemessenen Sterns) ab. Daher identifizierten wir zunächst 604 Absorptionslinien im Wellenlängenbereich von RAVE und verbesserten deren Oszillatorstärken durch eine inverse Spektralanalyse. Dann wurden die stellaren Parameter von RAVE verbessert, indem die RAVE Pipeline und die stellaren Parameter, auf denen sie beruht, modifiziert wurden. Die Änderungen eliminierten einen Teil der systematischen Fehler von stellaren Parametern, die im Laufe dieser Arbeit gefunden wurden. Um Elementhäufigkeiten zu bestimmen, haben wir zwei verschiedene Prozessierungs-Pipelines entwickelt. Beide berechnen die Elementhäufigkeiten unter der Annahme von Sternatmosphären im lokalen thermischen Gleichgewicht (local thermal equilibrium, LTE). Die erste Pipeline berechnete Elemenhäufigkeiten anhand der Äquivalentbreiten von Absorptionslinien. Da diese Methode eine geringe Empfindlichkeit für die Elementhäufigeiten relativ zu Eisen erreichte, wurde sie ersetzt. Die neue Pipeline benutzt chi^2-Fits von Modellspektren an die beobachteten Spektren. Dank Ihrer Präzision wurde diese für die Erstellung des RAVE-Katalogs von Elementhäufigkeiten verwendet. Diese Pipeline liefert Elementhäufigkeiten mit einer Genauigkeit von ~0.2dex, während für Spektren mit 20>S/N>40 immerhin noch ~0.3dex Genauigkeit erreicht werden. Für die vorliegende Arbeit wurden für 217.358 Sterne die Häufigkeiten von sieben chemischen Elementen bestimmt. Mit diesen Daten wurde der radiale chemische Gradient unserer Milchstraße untersucht. Wir finden, dass Sterne mit kleinen vertikalen Geschwindigkeiten |W|, die also nahe der galaktischen Ebene bleiben, einen radialen Gradienten der Eisenhäufigkeit zeigen, der mit früheren Studien übereinstimmt (~-0.07 dex Kpc^-1), während Sterne mit großen |W|, also solche, die größere galaktische Höhen erreichen, einen progressiv flachere Gradienten zeigen. Die Gradienten der anderen Element folgen dem gleichen Trend. Das lässt darauf schließen, dass entweder die Durchmischung der galaktischen dicken Scheibe effizient arbeitet oder aber dass die dicke Scheibe aus interstellarer Materie gebildet wurde, die chemisch recht homogen war. Speziell fanden wir hunderte von Sternen, die zwar kinematisch als zur dicken Scheibe zugehörig klassifiziert werden können, die aber die typische chemische Zusammensetzung der dünnen Scheibe aufweisen. Einige wenige dieser Sterne wurden bereits von anderen Autoren entdeckt, aber ihre Herkunft bleibt immer noch unklar. Eine Möglichkeit ist, dass die Sterne der dünnen Scheibe kinematische geheizt werden, sodass sie effizienter radial gemischt werden, was die chemischen Gradienten verwischt und auch flacher macht. Alternativ dazu könnten diese Sterne einer "Übergangspopulation" angehören, welche hinsichtlich der Scheibenevolution die Verbindung zwischen der dünnen und der dicken Scheibe darstellt. Unsere Untersuchung zeigt, dass sich diese beiden Erklärungen gegenseitig nicht ausschließen. Künftige Nachspektroskopierung mit hoher Auflösung wird die Rolle dieser Sterne in der Entwicklungsgeschichte der galaktischen Scheibe aufklären.
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Blanco-Cuaresma, Sergi. "Test de la technique de marquage chimique avec des amas ouverts." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0079/document.
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Contexte. Les étoiles naissent ensemble dans des nuages moléculaires géants. Si nous faisons l’hypothèse qu’ils étaient à l’origine chimiquement homogènes et bien mélangés, nous nous attendrions à ce que les étoiles issues d’un même nuage aient la même composition chimique. La plupart des groupes d’étoiles sont perturbés lors de leur évolution dans la galaxie et l’information dynamique est perdue. Ainsi la seule possibilité que nous ayons de reconstruire l’histoire de la formation stellaire est d’analyser les abondances chimiques que l’on observe aujourd’hui.But. La technique de marquage chimique a pour but de retrouver les amas d’étoiles dissociés en se basant uniquement sur leur composition chimique. Nous évaluons la viabilité de cette technique pour retrouver les étoiles qui sont nées dans un même amas mais qui ne sont plus gravitationnellement liées.Méthodes. Nous avons créé une librairie de spectres stellaires de haute qualité afin de faciliter l’évaluation des analyses spectrales. Nous avons développé notre propre outil d’analyse spectrale, nommée iSpec, capable d’homogénéiser les spectres stellaires venant de tous types d’instruments et de dériver les paramètres atmosphériques et les abondances chimiques. Finalement, nous avons compilé des spectres stellaires d’étoiles de 32 amas ouverts, nous avons dérivé de façon homogène les paramètres atmosphériques et les abondances de 17 espèces, et nous avons utilisé des algorithmes d’apprentissage automatique pour grouper les étoiles en se basant sur leur composition chimique.Résultats. Nous avons trouvé que les étoiles à des étapes d’évolution différentes ont des motifs chimiques distincts qui peuvent être dus à des effets NLTE,de diffusion atomique, de mélange et de corrélation à partir des déterminations de paramètres atmosphériques. Quand nous séparons les étoiles suivant leur stade d’évolution, nous observons qu’il y a un important degré de recouvrement dans la détermination des signatures chimiques des amas ouverts. Ceci rend difficile de retrouver les groupes d’étoiles nées ensemble en utilisant la technique de marquage chimiqueContext. Stars are born together from giant molecular clouds and, if weassume that they were chemically homogeneous and well-mixed, we expect them toshare the same chemical composition.Most of the stellar aggregates are disrupted while orbiting the Galaxy and thedynamic information is lost, thus the only possibility to reconstruct the stellarformation history is to analyze the chemical abundances that we observe today.Aims. The chemical tagging technique aims to recover disrupted stellarclusters based merely on their chemical composition. We evaluate the viability of thistechnique to recover conatal stars that are not gravitationally bound anymore.Methods. We built a high-quality stellar spectra library to facilitate theassessment of spectral analyses. We developed our own spectral analysisframework, named iSpec, capable of homogeneizing stellar spectra and derivingatmospheric parameters/chemical abundances. Finally, we compiled stellar spectrafrom 32 Open Clusters, homogeneously derived atmospheric parameters and 17abundance species, and applied machine learning algorithms to group the starsbased on their chemical composition. This approach allows us to evaluate theviability of the chemical tagging technique.Results. We found that stars in different evolutionary stages havedistinguished chemical patterns may be due to NLTE effects, atomic diffusion, mixingand correlations from atmospheric parameter determinations. When separating starsper evolutionary stage, we observed a high degree of overlapping among OpenCluster’s chemical signatures, making it difficult to recover conatal aggregates byapplying the chemical tagging technique
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Thévenin, Frédéric. "Contribution a l'etude des abondances des populations stellaires." Paris 7, 1987. http://www.theses.fr/1987PA077294.
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Presentation des resultats et difficultes rencontres en abordant les problemes d'evolution des galaxies et plus precisement de la galaxie. Un exemple d'application sur les etoiles naines f montre qu'elles ne subissent aucune anomalie d'abondances en elements lourds par la physique particuliere de leurs atmospheres. La spectrometrie a basse resolution ( equiv. A 2a) est abordee. Une application a la structure galactique et a la photometrie rgu de bale est presentee. Le spectrometre multifentes essefem qui repond au besoin de spectrographie statistique est presente et discut
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Guiglion, Guillaume. "Étude du disque galactique par marquage chimique de ses populations stellaires." Thesis, Nice, 2015. http://www.theses.fr/2015NICE4114/document.
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L'étude de la composition chimique et de la cinématique des étoiles de la Voie Lactée est essentielle afin de comprendre comment les grandes structures de notre Galaxie se sont formées. Les étoiles de faible masse gardent en mémoire dans leur atmosphère la composition chimique du milieu interstellaire dans lequel elles sont nées, et leur cinématique est essentielle afin de caractériser les différentes populations stellaires. Dans cette thèse, nous étudions le disque galactique, composante majeure de notre Galaxie. Dans le cadre de la mission spatiale Gaia, nous avons développé une procédure automatique de mesure d'abondances chimiques, GAUGUIN, utilisée dans le cadre du Gaia-ESO Survey GES (abondances chimiques d'éléments alpha et du pic du fer pour 10000 étoiles) et du projet AMBRE (abondances de lithium pour 7300 étoiles). GAUGUIN va être intégré au pipeline d'analyse des spectres RVS de Gaia. Nous avons étudié l'évolution des dispersions des vitesses dans le disque galactique en fonction du [Mg/Fe], utilisé comme proxy de l'âge. A partir de 6800 étoiles de GES, nous avons détecté la présence d'étoiles du disque épais cinématiquement froides mais avec des valeurs élevées du rapport [Mg/Fe], donc possiblement âgées. Dans le contexte d'un milieu turbulent, nous discutons la présence de ces étoiles dans le cadre des différents modèles de formation du disque galactique. Nous avons également montré que l'abondance du lithium dans le disque montre une croissance avec la métallicité sur le domaine -1<[M/H]<+0 dex et décroît pour les métallicités super-solaires. Enfin, le disque mince et le disque épais seraient caractérisés par des évolutions chimiques différentes en abondance de lithiumStudying both the chemical composition and kinematics of Milky Way stars is essential to understand how big structures of our Galaxy are formed. Indeed, low-mass stars retain in their photosphere the chemical composition of the interstellar medium is which they were born. Additionally, the kinematics are essential to characterize stellar populations. In this thesis, we focus on the galactic disc, a major component of the Milky Way. In the context of the Gaia mission, we have developed an automatic procedure GAUGUIN, devoted to deriving chemical abundances. We first applied our method to the Gaia-ESO Survey (GES) data to derive alpha and iron-peak chemical abundances for 10000 stars. We then derived lithium abundances for 7300 stars from the AMBRE project. GAUGUIN is well adapted to massive spectroscopic surveys, both in terms of computation time and accuracy. GAUGUIN will be soon integrated into the RVS DPAC analysis pipeline of the Gaia mission. We studied the velocity dispersions in the galactic disc as a function of the [Mg/Fe] ratio, used as an age proxy. Thanks to 6800 GES stars, we detected thick disc stars with cool kinematics and high [Mg/Fe] ratio, so presumably old. In the generally turbulent context of the primitive galactic disc, this thesis places these results in the framework of the different disc formation and evolution scenarios. We also showed that the lithium abundance in the galactic disc increases as a function of the metallicity in the domain -1<[M/H]+0 dex and decreases at super-solar metallicities. Finally, the thin and the thick discs could be characterized by different lithium abundance evolutions
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Santos-Peral, Pablo. "Archéologie galactique du disque de la Voie Lactée avec la mission spatiale Gaia." Thesis, Université Côte d'Azur, 2021. http://www.theses.fr/2021COAZ4001.
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L’Archéologie Galactique a pour objectif de révéler l’histoire de la Voie Lactée grâce à l’analyse de différentes propriétés stellaires: des abondances chimiques, de la cinématique, de la dynamique et de l’âge. En particulier, l’abondance d’éléments α (e.g. O, Mg, Si, S, Ca, Ti) par rapport au fer ([α/Fe]) est une importante signature fossile pour tracer l’évolution chimique des populations du disque Galactique, i.e. les disques épais et mince. Le but de cette thèse est d’explorer les différentes contraintes relatives à la determination précise d’abondances à partir des spectres stellaires observés et, en utilisant les donnés astrométriques de grand précision de la mission spatiale Gaia, analyser les propriétés chimique-dynamique du disque Galactique (e.g. gradients radiaux de abondance, rôle de la migration stellaire, relations âge-abondance) pour inférer la formation et évolution de la Voie Lactée.L’algorithm employé a été la procédure automatique d’estimation d’abondances GAUGUIN, qui fait partie d’analyse du RVS (Spectromètre de Vitesse Radiale) de la mission Gaia. En premier lieu, nous avons determiné les abondances de [Mg/Fe] pour 2210 étoiles observés dans le voisinage solaire par le spectrograph HARPS ESO (haute résolution spectrale: R ∼ 115000), et paramétrées par le Projet AMBRE (température effective, gravité de surface, métallicité globale [M/H], abondance [α/Fe], et vitesse radiale). Il a été trouvé que la définition de continuum pour normaliser les spectres observés est responsable de la majeure fraction d’incertitude dans l’estimation d’abondances pour les spectres d’étoiles riches en métaux. On montre une méthode qui améliore notablement la précision, et que nous permet d’observer une tendance décroissante de la abondance de [Mg/Fe] même à metallicités supérieures à la solaire ([M/H] > 0), à résoudre partiellement les divergences entre le plateau observé dans la literature, et la majeure pente prédite par les modèles d’évolution chimique de la Galaxie. Nous avons utilisé ces nouvelles mesures de [Mg/Fe] pour interpréter la fomation et l’évolution du disque Galactique. À cet effet, nous avons estimé des âges précises et des paramètres orbitaux pour 366 étoiles de la ‘main sequence turn-off’ (MSTO), en utilisant des isochrones PARSEC, ainsi que des données astrometriques et photométriques de Gaia DR2. Nous constatons un gradient plus escarpé de [Mg/Fe], par rapport aux valeurs de la literature, qui est un résultat direct de la amélioration des estimations d’abondances pour les étoiles riches en métaux. De plus, une dispersion significative des âges stellaires a été trouvé pour chaque valeur de [Mg/Fe], et aussi une claire corrélation de la dispersion d’abondances de [Mg/Fe] avec la métallicité pour un âge fixe. Tandis que pour [M/H] ≤ -0.2, une claire tendance âge-métellicité et âge-[Mg/Fe] est observée, des étoiles plus riches montrent des âges entre 3 jusqu’à 12 Gyr, en décrivant une tendance plate dans les relations [M/H]-age et [Mg/Fe]-age. De plus, nous trouvons une fraction significative d’étoiles ayant migré radialement dans le disque galactique, dont la distribution d’ages est très dispersée.Enfin, les résultats ont montré l’apparition d’une deuxième séquence chimique dans le disque extérieur, il y a 10-12 Gyr. Ces étoiles sont moins riches en métaux que la population stellaire coexistante dans les parts intérieures du disque, et montrent des valeurs inférieurs de [Mg/Fe] que les étoiles plus anciennes avec la même métallicité, en produisant une discontinuité chimique. Au vu de ces résultats, ils privilégient une formation rapide d’un disque primitif qui s’est développée dans les régions internes, suivie d’une accrétion de gaz pauvre en métaux, probablement lié à l’accrétion d’un satellite riche en gaz, qui a pu avoir déclenché la formation du disque minceGalactic archaeology aims at unveiling the history of the Milky Way by analysing different stellar properties: chemical abundances, kinematics, dynamics and ages. In particular, the abundance of α-elements (e.g. O, Mg, Si, S, Ca, Ti) with respect to iron ([α/Fe]) is an important fossil signature to trace the chemical evolution of the Galactic disc’s populations, i.e. the thin and the thick disc. The goal of this thesis is to explore the main issues concerning the determination of high-precision abundances from observed spectral data and, by using the high-quality astrometric data provided by the Gaia space mission, analyse the chemodynamical properties of the Galactic disc (e.g. radial abundance gradients, role of stellar migration, age-abundance relations) in order to infer the formation and evolution of the Milky Way.The implemented algorithm was the automated abundance estimation procedure GAUGUIN, which is integrated into the RVS (Radial Velocity Spectrometer) DPAC analysis pipeline of the Gaia mission. We first applied our method to derive [Mg/Fe] abundances for 2210 solar neighbourhood stars observed by the HARPS ESO spectrograph (high spectral resolution: R ∼ 115000), and parametrised by the AMBRE Project (effective temperature, surface gravity, overall metallicity [M/H], [α/Fe] abundance, and radial velocity). We found that the definition of continuum to normalise the observed spectra is responsible for the largest fraction of the uncertainty in the abundance estimate for the metal-rich stellar spectra. We show a methodology that significantly improve the abundance estimate precision, and allows to observe a decreasing trend in the [Mg/Fe] abundance even at supersolar metallicites ([M/H] > 0), partly solving the apparent discrepancies between the observed flat trend in the literature, and the steeper slope predicted by Galactic chemical evolution models.We used these new [Mg/Fe] abundance measurements to interpret the Galactic disc formation and evolution. To this purpose, we estimated ages and orbital properties for 366 main sequence turn-off (MSTO) stars, using PARSEC isochrones, together with astrometric and photometric values from Gaia DR2. We observe a steeper [Mg/Fe] gradient, compared to literature values, which is a direct result of the improvement of the abundance estimates in the metal-rich regime. Moreover, we find a significant spread of stellar ages at any given [Mg/Fe] value, and observe a clear correlated dispersion of the [Mg/Fe] abundance with the metallicity at a given age. While for [M/H] ≤ -0.2, a clear age-metallicity and age-[Mg/Fe] trends are observed, more metal-rich stars display ages from 3 up to 12 Gyr, describing an almost flat trend in the [M/H]-age and [Mg/Fe]-age relations. In addition, we found a significant fraction of radial migrated stars in the Galactic disc, for a wide range of stellar ages. Finally, we observe the appearance of a second chemical sequence at the outer disc, 10-12 Gyr ago. These stars are more metal-poor with respect to the coexisting stellar population in the inner parts of the disc, and show lower [Mg/Fe] abundances than prior disc stars of the same metallicity, leading to a chemical discontinuity. Our data favour the rapid formation of an early disc that settled in the inner regions, followed by the accretion of metal-poor gas, probably related to a major accretion event from a gas-rich satellite merger, that may have triggered the formation of the thin disc population
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Nandakumar, Govind. "L’archéologie galactique et son application au centre galactique." Thesis, Université Côte d'Azur (ComUE), 2018. http://www.theses.fr/2018AZUR4064/document.
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L'archéologie galactique consiste à disséquer et analyser les nombreuses composantes de la Voie Lactée afin de mettre en évidence et distinguer les processus physiques qui contribuent à sa formation et son évolution. Ceci est possible grâce à une estimation précise des positions, des vitesses ainsi que des propriétés de l'atmosphère stellaire des étoiles individuelles qui appartiennent aux différents populations stellaires qui composent chacune de ces composantes. De ce fait, ce domaine dépend non seulement d'observations photométriques, astrométriques et spectroscopiques permettant de mesurer en détail les propriétés stellaires mentionnées mais également de modèles théoriques précis afin de les confronter avec les données observationnelles. Au cours de cette thèse, j'ai mené une étude détaillée sur les effets de fonction de sélection sur les abondances métalliques en utilisant des sondages spectroscopiques aux grandes échelles, suivi d'observations spectroscopiques de petites et grandes résolutions sur les parties internes de la Voie Lactée afin de caractériser la nature chimique du bulbe galactique ainsi que le taux de formation stellaire dans la zone centrale moléculaire (CMZ). Avec les présents et futurs grands sondages dédiés à l'archéologie galactique tels que APOGEE, RAVE, LAMOST, GALAH, etc.., il est essentiel de connaître la fonction de sélection spécifique qui est associée à la stratégie de ciblage de chacun de ces sondages. En utilisant des champs communs et des lignes de visée similaires entre APOGEE, LAMOST, GES et RAVE, et tout en considérant des modèles de synthèse de population stellaire, J'ai étudié les effets de fonction de sélection sur la fonction de distribution de la métallicité (MDF) et sur le gradient vertical de métallicité dans le voisinage solaire. Mes résultats indiquent qu'il y a un négligeable effet de fonction de sélection sur la MDF ainsi que sur le gradient vertical de métallicité. Ces résultats suggèrent alors que différents sondages spectroscopiques (de différentes résolutions et de longueurs d'onde) peuvent être combinés dans des études similaires à condition que les métallicité soient placées sur la même échelle. Tandis que de plus en plus d'observations spectroscopiques des régions externes du bulbe de la Voie Lactée révèlent la complexité de sa morphologie, sa cinétique et de sa nature chimique, les études détaillées sur les abondances chimiques de la région interne du bulbe (400-500 pc) font en revanche défaut. Je présenterai alors des spectres de haute résolution dans la bande K d'étoiles géantes K/M issues de cette région obscure et obtenus à partir du spectrographe de haute résolution dans l'infrarouge, CRIRES (R-50,000) situé au VLT. Je discuterai ensuite la MDF et les abondances chimiques détaillées de notre échantillon dans cette région et également la symétrie Nord-Sud dans la MDF le long du petit axe du bulbe. Un enjeu majeur dans les modèles d'évolution chimique est le manque de connaissance vis à vis de l'histoire et du taux de la formation stellaire de la Voie Lactée. La partie centrale de la Voie Lactée (<200 pc), appelée communément la zone centrale moléculaire, possède un grand réservoir de gaz moléculaire avec des indications d'activités de formation stellaire durant les 100 000 dernières années. J'ai utilisé des spectres KMOS (VLT) de petite résolution afin d'identifier et analyser les objects stellaires jeunes et massifs (YSOs) et afin d'estimer le taux de formation stellaire dans la CMZ en utilisant la méthode de contage YSOGalactic archaeology deals with dissecting the Milky Way into its various components with the objective to disentangle processes contributing to the Milky Way formation and evolution. This relies on precise estimation of positions, velocities as well as stellar atmosphere properties of individual stars belonging to different stellar populations that make up each of these components. Thus this field relies on photometric, astrometric and spectroscopic observations to measure the above mentioned stellar properties in detail in addition to accurate models to compare the observed results with. In this thesis, I have carried out a detailed study of selection function effects on metallicity trends using larges scale spectroscopic surveys, followed by high and low resolution spectroscopic observations towards the inner Milky Way to characterise the chemical nature of the inner Galactic bulge and to measure the star formation rate in the central molecular zone (CMZ), respectively. With ongoing and upcoming large Galactic archaeology spectroscopic surveys such as APOGEE, RAVE, LAMOST, GALAH etc, it is essential to know the specific selection function which is related to the targeting strategy of each of them. By using common fields along similar lines of sight between APOGEE, LAMOST, GES and RAVE, and together with stellar population synthesis models, I investigate the selection function effect on the metallicity distribution function (MDF) and the vertical metallicitiy gradients in the solar neighborhood. My results indicate that there is negligible selection function effect on the MDF and the vertical metallicity gradients. These results suggest that different spectroscopic surveys (different resolutions and wavelength range) can be combined for such studies provided their metallicities are put on the same scale. While more and more spectroscopic observations of the outer bulge regions reveal the complex morphological, kinematic and chemical nature of the Milky Way bulge, there is a lack of detailed chemical abundances studies in the inner bulge region (400-500 pc). I will present high resolution K-band spectra of K/M giants in this highly obscured region obtained using the high resolution infrared spectrograph, CRIRES (R-50,000), on VLT. I will discuss the MDF and detailed chemical abundances of our sample in this region as well as the North-South symmetry in MDF along the bulge minor axis. A major challenge in the chemical evolution models is the lack of knowledge about the star formation history and the star formation rate in the Milky Way. The inner 200 pc of the Milky way, the so called central molecular zone, has a large reservoir of molecular gas with the evidence of star formation activity during the last 100,000 years. I used low resolution KMOS spectra (VLT) to identify and analyse massive young stellar objects (YSOs) and estimated the star formation rate in the CMZ using the YSO counting method
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Neves, Vasco. "Étude sur les paramétres stellaires des naines M et leur lien à la formation planétaire." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY082/document.
Full textAbstract:
Au moment d'écrire ma Thèse plus de 900 exoplanètes été annoncées et plus de 2700 planètes détectées par le télescope spatial Kepler sont en attente d'être confirmées. La haute précision des spectres et des courbes de lumière obtenue dans les relevés Doppler et transit, permet l'étude détaillée des paramètres des étoiles hôtes, et ouvre la possibilité d'enquêter sur les corrélations étoile planètes. En outre, la détermination des paramètres stellaires avec précision est un besoin critique pour déterminer les paramètres planétaires, à savoir, la masse, le rayon et la densité.Dans le cas des naines FGK, la détermination des paramètres stellaires est bien établie et peut être utilisée avec confiance pour étudier la relation planète-étoile ainsi que pour obtenir les paramètres planétaires avec une grande precision. Cependant, ce n'est pas le cas pour les naines M, les étoiles les plus communes de la Galaxie. Par rapport à leurs cousines plus chaudes, les naines M sont plus petites, plus froides, et plus faiblement lumineuses, et donc plus difficile à étudier. Le plus grand défi qui concerne les naines M est lié à la présence de milliards de lignes moléculaires qui gomme le continuum et rend l'analyse spectrale classique presque impossible. Trouver des fac ̧ons nouvelles et novatrices pour surmonter cet obstacle et obtenir une mesure des paramètres stellaires est l'objectif principal de cette Thèse .Pour l'atteindre, j'ai concentré mes recherches sur deux approches méthodologiques, photométrique et spectroscopiques. Mon premier travail avait pour objectif d'établir l'étalonnage de métallicité pho- tométrique précis. Par manque de binaires FGK+M avec de bonnes données photométriques je ne pouvais pas atteindre cet objectif. Il m'a cependant était possible, avec les données disponibles, de comparer les étalonnages photométriques déjà établies et légèrement améliorer le meilleur d'entre eux, comme décrit au Chapitre 3.Puis, je me suis concentré sur les approches spectroscopiques pour obtenir des paramètres stel- laires plus précis pour les naines M. À cette fin, j'ai utilisé des spectres HARPS de haute résolution et développé une méthode pour mesurer les lignes spectrales sans tenir compte du continuum . En utilisant cette méthode, je créé un nouvel étalonnage visible avec une précision de 0.08 dex pour [Fe/H] et 80 K pourTeff .Ce travail est détaillé dans le Chapitre 4.Finalement , j'ai également participé à l'amélioration des paramètres de l'étoile GJ3470 et de sa planète, où mon expertise dans les paramètres stellaires de naines M avait un rôle important. Les détails concernant cette enquête sont présentés dans le Chapitre 5At the time of writing of this Thesis more than 900 planets have been announced and about 2700 planets from the Kepler space telescope are waiting to be confirmed. The very precise spectra and light curves obtained in Doppler and transit surveys, allows the in-depth study of the parameters of the host stars, and opens the possibility to investigate the star-plant correlations. Also, determining the stellar parameters with precision is critical for more precise determinations of the planetary parameters, namely, mass, radius, and density.In the case of the FGK dwarfs, the determination of stellar parameters is well established and can be used with confidence to study the star-planet relation as well as to obtain precise planetary parameters. However, this is not the case for M dwarfs, the most common stars in the Galaxy. Compared to their hotter cousins, M dwarfs are smaller, colder, and fainter, and therefore harder to study. The biggest challenge regarding M dwarfs is related to the presence of billions of molecular lines that depress the continuum making a classical spectral analysis almost impossible. Finding new and innovative ways to overcome this obstacle in order to obtain precise stellar parameters is the goal of this Thesis.To achieve this goal I focused my research into two main avenues: photometric and spectroscopic methods. My initial work had the objective of establishing a precise photometric metallicity calibration, but I could not reach this goal, as I did not have enough FGK+M binaries with good photometric data. However, it was possible, with the available data, to compare the already established photometric calibrations and slightly improve the best one, as described in Chapter 3.Then, I focused on spectroscopic approaches with the aim of obtaining precise M dwarf parame- ters. To this end I used HARPS high-resolution spectra and developed a method to measure the spectral lines disregarding the continuum completely. Using this method I established a new visible calibration with a precision of 0.08 dex for [Fe/H] and 80 K for Te f f . This work is detailed in Chapter 4.Finally, I also participated in the refinement of the parameters of the star GJ3470 and its planet, where my expertise in stellar parameters of M dwarfs had an important role. The details regarding this investigation are shown in Chapter 5
No momento em que escrevo esta Tese, o número de planetas anunciados já ultrapassou os 900 e os cerca de 2700 candidatos detectados pelo telescópio espacial Kepler esperam por confirmação. Os espectros e as curvas de luz obtidos nos programas de procura de planetas permitem, também, o estudo em profundidade dos parâmetros das estrelas com planetas e abrem a possibilidade de investigar a relação estrela-planeta. Neste contexto, a determinação com precisão dos parâmetros estelares é crítica na determinação precisa dos parâmetros planetários, nomeadamente, a massa, o raio e a densidade.No caso das anãs FGK, os métodos de determinação dos parâmetros estelares estão bem estabelecidos e podem ser usados com confiança no estudo da relação estrela-planeta, assim como na obtenção de parâmetros planetários precisos. No entanto, não é esse o caso para as anãs M, as estrelas mais comuns da nossa Galáxia. Ao contrário das suas primas, as estrelas M são mais pequenas, frias e ténues e, assim sendo, mais difíceis de estudar. O grande entrave no estudo das estrelas M está relacionado com a presença de biliões de linhas moleculares que deprimem o contínuo espectral, fazendo com que uma análise espectral clássica se torne quase impossível. A procura de métodos inovadores que possibilitem ultrapassar este obstáculo, tendo em vista a obtenção de parâmetros precisos, é o objectivo desta Tese.Tendo em conta esse objetivo, foquei os meus esforços em duas linhas principais de pesquisa, baseadas em métodos fotométricos e métodos espectroscópicos. O meu trabalho inicial tinha como objetivo o estabelecimento de uma calibração fotométrica para a metalicidade, mas não me foi possível atingir esse objetivo, pois não tinha sistemas binários FGK+M suficientes com bons dados fotométricos. No entanto, foi possível, com os dados disponíveis, comparar as calibrações fotométricas existentes e refinar ligeiramente a melhor delas, como descrito no Capítulo 3.Após este trabalho passei a concentrar-me em técnicas espectroscópicas de obtenção de parâmetros estelares em estrelas M. Tendo em mente esse objetivo, usei espectros HARPS de alta resolução para desenvolver um novo método de medição de linhas espectrais independente do contínuo espectral. Seguidamente, usei este método no desenvolvimento de uma nova calibração de metalicidade e temperatura efectiva em estrelas M na região do visível, através da qual consegui atingir uma precisão de 0.08 dex para a [Fe/H] e de 80 K para a temperatura. Este trabalho está descrito no Capítulo 4.Ao mesmo tempo colaborei na determinação com precisão dos parâmetros da estrela GJ3470 e do seu planeta, onde a minha proficiência na determinação de parâmetros estelares em anãs M teve um papel importante. Os detalhes relacionados com este trabalho de investigação estão descritos no Capítulo 5
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Dias, Bruno Moreira de Souza. "Formation and evolution of globular clusters in the Galaxy and Magellanic Clouds." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-26082014-090039/.
Full textAbstract:
Globular clusters are tracers of the formation and evolution of their host galaxies. Kinematics, chemical abundances, age and position of the clusters allows tracing interactions between Milky Way and surrounding galaxies and outlines their chemical enrichment history. In this thesis we analyse mid-resolution spectra of about 800 red giant stars in 51 Galactic globular clusters. It is the first time that [Fe/H] and [Mg/Fe] derived in a consistent way are published for such a huge sample of globular clusters, almost 1/3 of the total number of catalogued clusters. Our metallicities are showed to be more precise than previous works based on mid-resolution spectroscopy. A turnover at [Fe/H] ~ -1.0 is found in the plot [Fe/H] vs. [Mg/Fe] for bulge and halo, although bulge seems to have a more metal-rich turnover, i.e, bulge has more efficient formation than the halo. Comparing the abundances with age the timescale for SNIa to start to become important is 1Gyr. [Fe/H] vs. age corroborates the different star formation efficiency of bulge and halo while [Mg/Fe] does not follow that. Halo was formed in mini halos or dwarf galaxies, and two multiple population clusters had their origin analysed to check it. M 22 seems to have been formed in the Milky Way while NGC 5824 possibly was originated in a dwarf galaxy, although our results are inconclusive for NGC 5824. The Galactic bulge seems to have been formed fast i.e., probably the oldest globular cluster is there. In fact HP 1 has a bluer horizontal branch than expected for its metallicity and we interpret that as an age effect. We determine its distance using light curves of variable stars in order to constrain future age determinations via colour-magnitude diagram. Finally, we investigate interaction between Milky Way and its neighbour galaxy SMC. We find that some star clusters are being stripped out of the SMC main body, which is consistent with tidal stripping scenario for the interaction between the galaxies, instead of ram pressure that would only affect gas.Aglomerados globulares são traçadores da formação e evolução de suas galáxias. Cinemática, abundâncias químicas, idades e posições dos aglomerados permitem traçar interações entre Via Láctea e galáxias vizinhas e suas histórias de enriquecimento químico. Nesta tese analisamos espectros de média resolução de mais de 800 estrelas gigantes vermelhas em 51 aglomerados globulares Galácticos. É a primeira vez que [Fe/H] and [Mg/Fe] determinados de modo consistente são publicados para uma amostra desse porte, ~1/3 dos objetos catalogados. Nossas metalicidades são mais precisas que trabalhos anteriores similares. Uma quebra em [Fe/H] ~ -1.0 é encontrada no gráfico [Fe/H] vs. [Mg/Fe] para o bojo e halo, embora bojo parece ter uma quebra em [Fe/H] maior, i.e, bojo tem formaçãao mais eficiente que o halo. Comparando abundâncias com idade, a escala de tempo para SNIa ficar importante é 1Gano. [Fe/H] vs. idade corrobora diferentes eficiências de formação do bojo e halo, mas [Mg/Fe] vs. idade não mostra isso. O halo foi formado em mini halos ou galáxias anãs, e dois aglomerados com dispersão em [Fe/H] tiveram suas origens analisadas. M 22 parece ter sido formado na Via Láctea e NGC 5824 possivelmente foi originado em uma galáxia anã, embora os resultados são inconclusivos para NGC 5824. O bojo parece ter sido formado rapidamente e deve possuir o aglomerado mais velho. De fato, HP 1 tem um ramo horizontal mais azul que o esperado para sua metalicidade e vemos isso como um efeito da idade. Determinamos sua distância usando curvas de luz de RR Lyrae de maneira a restringir futuras determinações de idade via diagrama cor-magnitude. Finalmente, investigamos a interação entre Via Láctea e sua galáxia vizinha SMC. Encontramos aglomerados sendo removidos do corpo central da SMC, consistente com cenário de remoção por força de maré para a interação entre as galáxias, em vez de ``ram pressure\'\' que afeta só gás.
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Evans, Ian Nigel. "Calibration of the H II region abundance sequence and abundances in Seyfert galaxies." Phd thesis, 1986. http://hdl.handle.net/1885/138350.
Full textAbstract:
An extensive, homogeneous grid of theoretical photoionization models
with conditions appropriate to observed H n regions is computed. This grid
is used to develop a comprehensive set of theoretical diagnostic diagram s for
H ii regions which employ ratios of prom inentemission lines to determine the
ionization parameter within the nebula, and the ionization temperature of its
exciting star(s). It is also possible to estimate the element-averaged m etallicity
in the nebula and stars from these diagnostics. Theoretical loci for
H ii regions on the principal excitation diagrams of Baldwin, Phillips, and
Terlevich (1981) are constructed and confirm th at the theoretical models
overlie the observed distribution of H u regions on these diagrams. Comparison
of current observational data with the theoretical models on these
and other diagrams implies the existence of a correlation between elementaveraged
metallicity and mean ionization parameter. The data also suggest
that the ionization temperature of the exciting star(s) in the ionizing
OB associations of H ii regions is approximately constant and independent of
metallicity and ionization parameter for the range of conditions considered
here.
A multiline fit to the observed emission-line spectral sequence of extragalactic
H u regions is generated. It is possible to produce an excellent
fit between the (rather narrow) emission-line ratio sequences that are observed
and the theoretical sequences, provided that the average ionization
parameter is strongly coupled w ith metallicity, and provided that nitrogen
is a product of secondary nucleosynthesis. Using this theoretical sequence of
H ii region models, the semiempirical abundance diagnostic ratios used by Al-loin et al. (1979), Pagel et al. (1979), and McCall, Rybski, and Shields (1985) are recalibrated and new abundance diagnostic ratios formulated. The correlation
between ionization parameter and abundance is found to have the
effect of changing the previous abundance calibration toward lower abundances,
particularly for the most metal-rich H ii regions. A new technique to
derive abundances from H n region spectra is suggested.
Oxygen and other heavy element abundances in a selection of well
observed H n regions in M101 are determined from the theoretical abundance
sequence calibration. Comparison of abundances derived from the
sequence with abundances derived from “exact” photoionization modeling
demonstrate that the accuracy with which H ii region abundances may be
derived from the sequence is ~ 0.15 dex. The data are employed to measure
radial abundance gradients and heavy element yields for oxygen, nitrogen,
and sulfur in M101. The combined abundance gradient and heavy element
yield data suggest that the production of elements by massive stars (oxygen,
neon) is enhanced in the inner regions of the disk of M101, whilst the
production of heavy elements (S, Ar, Ca, Fe) by low and intermediate mass
stars is enhanced in the outer disk. A simple model for galaxy disk formation
is suggested which is at least qualitatively capable of explaining these
observations. The theoretical abundance sequence calibration is also applied to optical
spectrophotometry of 23 H ii regions located in the inner disk regions of
two Seyfert 1 and two Seyfert 2 galaxies, including the prototype Seyfert 2,
NGC 1068, in order to determine oxygen, nitrogen, and sulfur abundances.
The mean oxygen abundance derived for each galaxy is shown to range between
solar abundance and twice solar abundance. There is no evidence for
abnormal N /O or S/O abundance ratios in any of the H ii regions observed. The observations suggest that the abundances derived for the H n regions
may be adopted as nuclear abundances and employed to constrain theoretical
models of the Seyfert nucleus. The observations then place limits on the
influence which the active nucleus can have on chemical enrichment of the
local interstellar medium.
Observations of the candidate near-nuclear H n regions in the disk of
NGC 1068 also indicate the presence of high-excitation extra-nuclear emission.
The optical spectra appear to be very similar to ordinary H n region
spectra with the addition of strong lines of [Ne v] AA3346,3426 and He n
A4686. This is interpreted as the superposition of an H u region spectrum
with the high-excitation emission, and theoretical nebular models are presented
which suggest that the high-excitation gas is most likely photoionized
by a power-law spectrum , probably from the nearby Seyfert nucleus.
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Hempel, Angela [Verfasser]. "Classification and abundance of extremely red galaxies with R-J ≥ 5 / presented by Angela Hempel." 2004. http://d-nb.info/973946733/34.
Full text
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Grossauer, Jonathan. "Abundance Matching with the Galaxies of the Virgo Cluster and the Stellar-to-Halo Mass Relation." Thesis, 2012. http://hdl.handle.net/10012/7062.
Full textAbstract:
Using data from the Next Generation Virgo Cluster Survey and high-resolution simulations of Virgo cluster-like halos, we determine the stellar-to-halo mass relation (SHMR) for subhalos, using the technique of abundance matching. The subhalo SHMR differs markedly from its field galaxy counterpart, regardless of how the subhalo mass is defined (mass at z = 0, mass at infall, or maximum mass while in the field). The slope of the relation at low mass (M⋆<10^10 Msun) is in all cases steeper than the same for the field. We find conflicting indicators of whether this difference in slope indicates an increasing or decreasing dark-to-stellar ratio; further modelling is required to reach a definitive conclusion. We also find evidence for the existence of a measurable age gradient in velocity, such that older subhalos have lower velocities than their younger peers. This opens the possibility that good quality redshifts of the lower mass galaxies of the Virgo cluster might provide additional constraints on the SHMR at high redshift and its evolution. Finally, we investigate the degree to which mergers, particularly major mergers, cause mixing of old and new material in halos, which has implications for the robustness of any implied radial age gradient. We find only a slight increase in mixing for major mergers over minor mergers, and little evidence for any large amount of mixing being induced by mergers of any ratio.
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"Green Pea Galaxies: Physical Properties of Low-redshift Analogs of High-redshift Lyman-alpha Emitters." Doctoral diss., 2018. http://hdl.handle.net/2286/R.I.50582.
Full textAbstract:
abstract: Green pea galaxies are a class of rare, compact starburst galaxies that have powerful optical emission line [OIII]$\lambda$5007. They are the best low-redshift analogs of high-redshift (z$>$2) Lyman-alpha emitting galaxies (LAEs). They provide unique opportunities to study physical conditions in high-redshift LAEs in great detail. In this dissertation, a few physical properties of green peas are investigated. The first study in the dissertation presents star formation rate (SFR) surface density, thermal pressure in HII regions, and a correlation between them for 17 green peas and 19 Lyman break analogs, which are nearby analogs of high-redshift Lyman break galaxies. This correlation is consistent with that found from the star-forming galaxies at z $\sim$ 2.5. In the second study, a new large sample of 835 green peas in the redshift range z = 0.011 -- 0.411 are assembled from Data Release 13 of the Sloan Digital Sky Survey (SDSS) with the equivalent width of the line [OIII]$\lambda$5007 $>$ 300\AA\ or the equivalent width of the line H$\beta$ $>$ 100\AA. The size of this new sample is ten times that of the original 80 star-forming green pea sample. With reliable T$_e$-based gas-phase metallicity measurements for the 835 green peas, a new empirical calibration of R23 (defined as ([OIII]$\lambda$$\lambda$4959,5007 + [OII]$\lambda$$\lambda$3726,3729)/H$\beta$) for strong line emitters is then derived. The double-value degeneracy of the metallicity is broken for galaxies with large ionization parameter (which manifests as log([OIII]$\lambda$$\lambda$4959,5007/[OII]$\lambda$$\lambda$3726,3729) $\geq$ 0.6). This calibration offers a good way to estimate metallicities for extreme emission-line galaxies and high-redshift LAEs. The third study presents stellar mass measurements and the stellar mass-metallicity relation of 828 green peas from the second study. The stellar mass covers 6 orders of magnitude in the range 10$^{5}$ -- 10$^{11}$ M$_{\odot}$, with a median value of 10$^{8.8}$ M$_{\odot}$. The stellar mass-metallicity relation of green peas is flatter and displays about 0.2 - 0.5 dex offset to lower metallicities in the range of stellar mass higher than 10$^{8}$ M$_{\odot}$ compared to the local SDSS star-forming galaxies. A significant dependence of the stellar mass-metallicity relation on star formation rate is not found in this work.Dissertation/Thesis
Doctoral Dissertation Astrophysics 2018
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Günthardt, Guillermo Iván. "Espectroscopía y fotometría de galaxias peculiares /." Doctoral thesis, 2008. http://hdl.handle.net/11086/120.
Full textAbstract:
Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2008.Se realizó una selección de 70 sistemas interactuantes de tipo M51 y se hizo un estudio fotométrico en el infrarrojo cercano, donde se compararon los colores 2MASS de este tipo de sistemas con los de galaxias aisladas. También se obtuvo información espectrofotométrica en el óptico para 13 objetos de este tipo de categoría de interacción y se construyó un catálogo de 20 sistemas, a partir del cual se estudió la cinemática de las distintas componentes.
Guillermo I. Günthardt, director Rubén J. Díaz.
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Άκρας, Σταύρος. "Ανίχνευση και μελέτη φαινομένων μεσοαστρική ύλης." Thesis, 2010. http://nemertes.lis.upatras.gr/jspui/handle/10889/3289.
Full textAbstract:
Ο σκοπός της παρούσας διδακτορικής διατριβής ήταν η μελέτη δύο σημαντικών φαινομένων μεσοαστρική ύλης όπως είναι τα Πλανητικά Νεφελώμάτα (ΠΝ) και η ράβδος των σπειροειδών γαλαξιών. Πιο συγκεκριμένα, μελετήθηκαν 44 ΠΝ στην περιοχή του Γαλαξιακού σφαιροειδούς (Boumis et al. 2003; 2006) και προσδιορίστηκαν οι φυσικοί παράμετροι τους, όπως είναι η ενεργός θερμοκρασία και η λαμπρότητα του κεντρικού αστεριού, η πυκνότητα και η θερμοκρασία των ηλεκτρονίων, η αφθονία των Ηe, N, O, S κτλ., χρησιμοποιώντας το μοντέλο φωτο-ιονισμού Cloudy (Akras et al. 2010a). Επίσης, μελετήθηκε η ράβδος των γαλαξιών, χρησιμοποιώντας το μοντέλο διάδοσης ακτινοβολίας CRETE, με σκοπό να ερευνηθεί πώς η ύπαρξη της ράβδου επηρεάζει την μορφολογία των γαλαξιών και την σκόνη τους. Ταυτόχρονα, προσδιορίστηκαν οι παράμετροι της ράβδου, όπως το μήκος, το ύψος, η γωνία κλίσης και η γωνία θέσης της για 4 ραβδωτούς σπειροειδείς γαλαξίες (NGC 4013, UGC 2048, IC 2531 και το Γαλαξία μας).
Στο πρώτο μέρος της μελέτης, διαχωρίστηκαν τα ΠΝ ανάλογα με την μορφολογία τους σε σφαιρικά, ελλειπτικά και διπολικά και βρέθηκε ότι η αφθονία του Ηe και του Ν είναι μεγαλύτερη στην τελευταία κατηγορία σε σχέση με τις υπόλοιπες. Επιπλέον, η χρήση του στατιστικού εργαλείου PCA, έδειξε ότι τα κυκλικά και τα ελλειπτικά ΠΝ διαχωρίζονται από τα διπολικά, βάσει της τιμής του λόγου log(Ν/Ο), ο οποίος παίρνει αρνητικές και θετικές τιμές για τα διπολικά, ενώ μόνο αρνητικές τιμές στις υπόλοιπες κατηγορίες. Η κρίσιμη τιμή βρέθηκε ίση με -0.18 dex και αντιστοιχεί σε μάζα προγενέστερου αστεριού ίση με 2.6 (Akras & Boumis 2007).
Στο δεύτερο μέρος, περιγράφηκε η ράβδος των γαλαξιών χρησιμοποιώντας την συναρτησιακή ελλειψοειδής υπερβολής. Μεταβάλλοντας την γωνία κλίσης του γαλαξία, η δομή σχήματος «Χ», η οποία παρατηρείται στις ράβδους, μπορεί να παρατηρηθεί μόνο για γωνίες μεγαλύτερες από 60ο.
Επιπρόσθετα, στην περίπτωση του Γαλαξία μας, βρέθηκε ότι η γωνία θέσης της ράβδου είναι γύρω στις 25ο και το μήκος της 3.75 kpc (Akras et al. 2010b). Λαμβάνοντας υπόψη ότι η μέση τιμή του μήκους της ράβδου στους γαλαξίες είναι μεταξύ 3.0 και 4.0 kpc, προκύπτει ότι για τον NGC 4013 η γωνία θέσης του είναι μεταξύ 5 και 10 μοίρες, για τον UGC 2048 μεταξύ 40 και 50 μοίρες, για τον IC 2531 35 και 45 μοίρες ενώ τέλος για το Γαλαξία μας υπολογίζεται μεταξύ 20 και 30 μοίρες (Akras et al. 2010b).The aim of this PhD thesis was the study of two very important interstellar medium phenomena like the Planetary Nebulae (PNe) and the stellar bar in spiral galaxies. In particular, we studied 44 PNe in the Galactic bulge region and we determined their physical parameters, like the effective temperature and luminosity of the central star, the electron temperature and density, the abundance of He, N, O, S etc., using the photo-ionization model “Cloudy” (Akras et al. 2010a). It was also pursued to study the stellar bar component using the 3D radiative transfer model CRETE, in order to investigate the effects of a stellar bar component to the morphology of the galaxy and its dust content. In addition, the parameters of the bar component such as the length, the height, the inclination angle and the position angle were determined for four spiral galaxies (NGC 4013, UGC 2048, IC 2531 and our Galaxy). In the first part of the thesis, the PNe were separated according to their morphology (spherical, elliptical and bipolar shape) and we found that the He and N abundances are greater in bipolar PNe. Moreover, by using the statistical tool PCA, it was found that the circular and the elliptical PNe are different from the bipolar, since the log(O/N) takes negative values in the first two and positive or negative values in the bipolar PNe. The critical value was found at -0.18 dex, which corresponds to a stellar mass of 2.6 (Akras & Boumis 2007). In the second part, we managed to accurately describe the morphology of the bar component by using the function of hyperbolic ellipse. For different inclination angles of the observed galaxies, it was found that the “X-shape" feature can be seen only in the case where the inclination angle is greater than 60 degrees. In the case of Milky Way, it was found that the position angle of the bar is approximately 25 degrees and the length equals to 3.75 kpc (Akras et al. 2010b). Considering that the mean length of the bar component is equal to 3.0-4.0 kpc, it was determined that the position angle of a) NGC 4013 takes values between 5 and 10 degrees, b) UGC 2048 takes values between 40 and 50 degrees, c) IC 2531 takes values between 35 and 45 degrees, and our Galaxy takes values between 20 and 30 degrees (Akras et al. 2010b).
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Nicholls, David Conway. "Nebular metallicities in isolated dwarf irregular galaxies." Phd thesis, 2014. http://hdl.handle.net/1885/11923.
Full textAbstract:
The motive for this work was to investigate whether small, isolated gas-rich galaxies show
evidence of chemical evolution, by studying their nebular metallicities. I have identified
a sample of 83 objects chosen for low luminosity and mass, the presence of active star
formation, and isolation from other galaxies and galaxy clusters that might generate tidal
effects or enrich the intergalactic medium. From these I have measured the spectra of 35
objects, using theWiFeS IFU spectrograph on the ANU 2.3m telescope at Siding Spring.
In analysing spectra extracted from the WiFeS data cubes, I found that standard ‘strong
line’ methods using emission line ratios to measure atomic abundances, gave either erratic
or no results. I found that for those galaxies showing the [O iii] 4363Å auroral line, the
metallicities determined using the standard ‘electron temperature’ methodwere inconsistent
with previous published work. This led me to investigate the conventional assumption that
electrons in Hii regions are in thermal equilibrium. I show that the non-equilibrium ‘ ’
electron energy distribution, found almost universally in solar system plasmas, can explain
the long recognised ‘abundance discrepancy’ between recombination line and collisional line
abundance calculations in nebular metallicity measurements. This has added an important
new dimension to the analysis of nebular spectra.
Using the extensively revised Mappings photoionisation modelling code and new atomic
data to analyse the spectra of two exceptionally isolated dwarf galaxies, I find that they
exhibit metallicities similar to galaxies in more crowded environments, and appear to have
evolved quite normally, through periodic star formation and subsequent enrichment of
their interstellar media.
I present a new approach for calculating total oxygen abundance using electron temperatures
that appears to give more consistent results than earlier methods. I apply this to my
measured spectra, together with the revised Mappings photoionisation modelling code, to
explore the physical parameters affecting the measurement of nebular metallicities. In particular,
I find strong evidence for several of the observed nebulae being—in part—optically
thin. I use the models to show that nebular optical depth affects measured abundances and
temperatures, and that electron densities also have an important role. I develop models that
give a very good match to the observations.
I conclude that the measurement of abundances and temperatures in Hii regions is a more
complex question than had generally been assumed, and important physical parameters
affecting the measurement processes have in the past not been taken fully into account.
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Sakari, Charli. "Chemical Abundances of Local Group Globular Clusters." Thesis, 2014. http://hdl.handle.net/1828/5621.
Full textAbstract:
Detailed chemical abundances of globular clusters in the Milky Way and M31 (the Andromeda Galaxy) are presented based on analyses of high resolution spectra. The
unusual Milky Way cluster Palomar 1 (Pal 1) is studied through spectra of individual
red giant branch stars; these abundances show that Pal 1 is not a classical globular
cluster, and may have been accreted from a dwarf satellite of the Milky Way.
The Milky Way globular clusters 47 Tuc, M3, M13, NGC 7006, and M15 are studied
through their integrated light (i.e. a single spectrum is obtained for each cluster) in order
to test high resolution integrated light analyses. The integrated abundances from
these clusters reproduce the average abundances from individual stellar analyses for
elements that do not vary within a cluster (e.g. Fe, Ca, and Ni). For elements that do
vary within the clusters (e.g. Na and Mg) the integrated abundances fall within the
observed ranges from individual stars. Certain abundance ratios are found to be extremely sensitive to uncertainties in the underlying stellar populations, such as input
models, empirical relations to determine atmospheric parameters, interloping field stars, etc., while others (such as [Ca I/Fe I]) are largely insensitive to these effects.
With these constraints on the accuracy and precision of high resolution integrated
light analyses, detailed abundances are obtained for seven clusters in the outer halo
of M31 that were recently discovered in the Pan-Andromeda Archaeological Survey
(PAndAS) and are likely to have originated in dwarf galaxy satellites. Three clusters
are relatively metal rich ([Fe/H] > −1.5) for their locations in the outer halo; their
chemical abundances suggest that they likely originated in one or more fairly massive
dwarf satellities. The other four are more metal-poor, and may have originated in less
massive dwarf satellites. These results indicate that the Milky Way and M31 have
both experienced some amount of accretion from dwarf satellites, though M31 may
have had a more active accretion history.Graduate
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Ratsimbazafy, Ando Lalaina. "Luminous red galaxies in simulations." Thesis, 2010. http://hdl.handle.net/11394/3483.
Full textAbstract:
>Magister Scientiae - MScThere have been a number of attempts to measure the expansion rate of the Universe using age-dating of Luminous Red Galaxies (LRGs).Assuming stars in LRGs form at the same time, age-dating of two populations of LRGs at different redshifts can provide an estimate of the time difference associated with the corresponding redshift interval (dt/dz). This gives a direct estimate of the Hubble parameter at the average redshift of the two populations. In this thesis, we explore the validity of the assumptions in this method using LRGs identified in the Millenium Simulation.We study the properties of LRGs simulated using two semi-analytical models for galaxy evolution and discuss LRG selection criteria. We use stellar population modelling and spectral synthesis to estimate the errors on ages that can be expected and discuss optimization of an age-dating experiment.We find that H(z) using simulated galaxies from MS can be recovered with high accuracy. Using Single Stellar Populations (SSPs) to age -date LRGs is not sufficient for this experiment but if the star formation histories of galaxies are used, accurate ages are obtainable. We discuss an observing program to carry out this experiment using SALT (Southern African Large Telescope).
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CURTI, MIRKO. "Assessing the chemical evolution of galaxies with large spectral surveys and spatially resolved observations." Doctoral thesis, 2018. http://hdl.handle.net/2158/1119026.
Full textAbstract:
Galaxies continuously undergo chemical enrichment. Heavy elements are produced in stars during their lifetime and then dispersed by means of stellar winds and supernovae, contributing to the enrichment of the surrounding interstellar medium (ISM). Gas flows, including inflows from the cosmic web and supernovae- or AGN-driven outflows, also play a crucial role in the definition of the chemical enrichment level by acting as regulators of both the gas content and the amount of metals that galaxies are capable to retain in the gas-phase of the ISM. Therefore, the gas-phase metallicity represents a fossil record of the recent star formation history of a galaxy and is strongly sensitive to all the physical processes which shape and drive the baryon-cycle in the Universe. Indeed, this mutual correlation between stellar activity, mass growth, metal production and gas flows gives rise to the well established scaling relations between mass, metallicity and star formation rate observed and thoroughly investigated both in the local Universe and at higher redshifts, whose characterization can provide crucial constraints on models and simulations aimed at describing how galaxies evolve across the epochs.
In this thesis we address some of the currently most debated topics related to the chemical evolution of star forming galaxies, by means of statistically robust analysis of large samples of local objects from the Sloan Digital Sky Survey (SDSS) and of near- infrared, spatially resolved spectroscopy of high-redshift sources, obtained from new generation instruments like KMOS on the Very Large Telescope and ARGOS on the Large Binocular Telescope.
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Berg, Trystyn Andrew Munro. "Metal Strong Damped Lyman Alpha Systems And Their Context With The Local Group." Thesis, 2014. http://hdl.handle.net/1828/5308.
Full textAbstract:
Damped Lyman α systems (DLAs) are useful probes of the chemical enrichment of the universe as they provide accurate abundance measurements of many chemical species. Using a sample of 30 DLAs (with large metal column densities) observed with the High Resolution Echelle Spectrometer on the Keck I telescope, the abundances of several elements (i.e. iron, zinc, chromium, silicon, sulphur, phosphorus, manganese, and boron) are derived and presented. A comparison is drawn between the abundances from these metal-rich DLAs with literature samples encompassing the largest compilation of high resolution observations of other DLAs, and stars from the Milky Way and its satellite galaxies to understand the astrophysical nature of DLAs.
Furthermore, the first ever extragalactic study of boron is presented. Using the sample of 30 metal-rich DLAs, two 3σ detections and one near detection 2.97σ) were found. From the comparison of [B/O] and, for the first time, [B/S], with studies in the Milky Way, there appears to be an excess of boron relative to its parent nucleus (oxygen) in these three DLA systems, suggesting that there may be a higher cosmic ray flux in DLAs than in the Milky Way.Graduate
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