Dissertations / Theses on the topic 'Galactic formation'
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Peschken, Nicolas. "Formation and evolution of galactic discs." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4732/document.
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Cette thèse explore la formation, l’évolution et la structure des galaxies spirales à l’aide de simulations, en mettant l’accent sur le disque. Elle s'appuie sur nos simulations hydrodynamiques à N-corps mettant en scène une fusion majeure entre deux galaxies à disque à haut redshift, chacune en possession d’un halo de gaz chaud. Les disques des progéniteurs sont détruits par la fusion, et un disque étendu se forme dans la galaxie ainsi obtenue à partir d’étoiles nouvellement formées, la formation stellaire étant alimentée par le halo de gaz. A la fin de la simulation, la nouvelle galaxie montre toutes les propriétés d’une galaxie spirale, prouvant pour la première fois avec des simulations comment une galaxie de type tardif peut être créée par une fusion majeure.Dans cette thèse sont analysées plusieurs propriétés des galaxies ainsi obtenues, comme la migration stellaire, la rotation angulaire de la barre, et les profils radiaux de densité surfacique. Ce dernier point en particulier constitue une partie importante de mon travail, le fit de ces profils permettant d'obtenir les grandeurs caractéristiques du disque. Nos disques montrent en effet un profil de type II (troncature vers le bas) dont il est possible d'extraire les longueurs d'échelle et le rayon de troncature. Le but est notamment de chercher ce qui module les valeurs de ces paramètres (ceux-ci étant très différents d'une simulation à l'autre), ainsi que les phénomènes à l'origine de ce profil spécifique. Enfin, certains disques de type III (troncature du profil vers le haut) obtenus pour des simulations de galaxies isolées sont présentés et analysés, afin de comprendre leur provenanceThis thesis explores the formation, evolution and structure of spiral galaxies using simulations, with an emphasis on the disc component. It is based on our N-body/SPH simulations involving a major merger between two disc galaxies at high redshift, both in possession of a hot gaseous halo. The discs of the progenitors are destroyed by the merger, and a well-extended disc forms in the remnant galaxy from newly born stars, star formation being fuelled by the gaseous halo. By the end of the simulation, the remnant galaxy shows all the properties of a spiral galaxy, proving for the first time in simulations how a late-type galaxy can be created from a major merger.In this thesis, several properties of the remnant galaxy are analysed, such as the stellar migration, the bar pattern speed, and the surface density radial profiles. This last point in particular represents a significant part of my work, using fits of the profiles to obtain the characteristic parameters of the disc. Our discs show a type II profile (downbending truncation), so that we can derive their scalelengths and truncation radius. The goal is to understand what determines the values of these parameters (which are very different from one simulation to another), as well as the origin of this specific profile. Finally, some type III discs (upbending truncation) obtained for simulations of isolated galaxies are presented and analysed, in order to investigate their formation mechanism
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Puxley, Philip John. "Vigorous star formation in galactic nuclei." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/27222.
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Barnes, A. T. "A comparison of star formation within the galactic centre and galactic disc." Thesis, Liverpool John Moores University, 2018. http://researchonline.ljmu.ac.uk/8633/.
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Stars are of fundamental importance to the entire field of astronomy. The conversion of elements and the distribution of energy throughout the lifetime of stars drives the evolution of the Universe. Despite this, we do not have a unified understanding of the formation process for all stars. This thesis attempts to move forward this understanding, by focussing on the question: How do the initial conditions of star-forming regions vary across environments, and do these influence the process of star formation? To investigate the initial conditions of star formation, regions on the verge of forming stars have to be first identified and analysed. These regions have to be untouched by the disruptive effects of stellar feedback, such that the natal conditions of the gas – e.g. kinematics and chemistry – are not destroyed. Quiescent regions that are expected to form low-mass stars have been well studied over the past few decades, and the general process of low-mass star formation is well understood. Only relatively recently, however, has a group of objects being identified as being potential hosts of these initial stages of high-mass star formation: Infrared Dark Clouds (IRDCs). The study of these objects is difficult, due to both their rarity and complexity. An end-to-end understanding of high-mass star formation is, therefore, much less developed compared to their lower mass counterparts. This thesis presents the study of a sample of IRDCs within the Disc and Centre of the Milky Way; two very different environments. Several key aspects of the star formation process within IRDCs from these environments are investigated. Firstly, a chemical signpost – the deuterium fraction of N2H+ – is used to identify the regions of dense and cold gas on the verge of forming high-mass stars within a quiescent Disc IRDC, which can be used to study the initial conditions for star formation. Omitting potential beam dilution effects, chemical modelling suggests that the cloud could have reached a global chemical equilibrium, and, if so, would also be dynamically old (survived for several free-fall times). This timescale, with estimates of the embedded stellar mass, is used to determine star formation rates and efficiencies. Secondly, the kinematic structures within two apparently similar Disc IRDCs are identified using dense gas tracers – C18O and N2H+. The properties of these structures appear to be very similar, hinting at a similar formation scenario for both clouds, or, potentially, that these may be inherent to the larger Disc IRDC population. The dynamics of these filaments also show that they may be merging, which would suggest a compressive mode of turbulence driving. These structures are then linked to the larger kinematic structures – identified using a lower density tracing molecule, 13CO – and found to show good coherence with the brightest, most extended structures. These are then placed in the context of the previously identified Galactic scale structures, and in doing so show that IRDCs could be the densest parts of the much larger arm or inter-arm filamentary structures. Thirdly, the level of star formation within the Galactic Centre is investigated on both global (∼ 100 pc) and local (∼ 1 pc) scales. On a global scale, the star formation rate has been determined from all the available observational star formation diagnostics – i.e. direct counting of young stellar objects and integrated light measurements – and found to be in agreement with previous studies; i.e. around one-to-two orders of magnitude lower than predicted by the star formation models. On individual cloud scales, the star formation efficiency per free-fall time is in better agreement with the model predictions. However, uncertainties on the properties of these regions, such as the mode of turbulence driving, limit the further verification or falsification of the star formation theories. Lastly, the investigation of the local scale star formation within the Galactic Centre highlighted a particular part of the parameter space as the most promising to further test the star formation theories. In light of this, high-spatial resolution ALMA observations have been taken of two Galactic Centre clouds within this regime. Early results show that they have a complex structure, similar to that seen within Disc IRDCs, containing both filamentary and core-like features. Investigation of the brightest, most compact core region shows that it contains a very rich chemistry, and, of particular interest, is the rigorous detection of the pre-biotic molecule formamide (NH2CHO). When placing the results of this thesis in the bigger context of star formation theory, they appear to show interesting implications for the initially posed question – what is the influence of environment on the process of star formation? It is found here that despite the very different cloud scale properties of these regions, the star formation efficiency per free-fall time is surprisingly similar. To investigate this, the properties of the individual sites of high-mass star formation, the high-mass star-forming cores, are compared. Interestingly, despite the different environmental conditions, several key properties of the cores, such as their size and mass distribution, are also found to be very similar. The similarity of high-mass core properties and star formation rate per free fall time implies that once a region has produced high-mass cores, the evolution of these cores towards star formation must be similar. The difference in the global/environmental properties of the gas must then be setting the total star formation rate within these regions, by limiting the number of cores that can form. In particular, the mode of turbulence driving may play a major role in governing the fraction of gas that can be converted into stars per free-fall time within these two environments.
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Haehnelt, Martin. "Quasars and the formation of galactic nuclei." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319491.
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Brown, Richard Joseph Norman. "The formation and evolution of elliptical galaxies." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273922.
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Quinn, Lyshia Jane. "Maser hunting in the galactic plane." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/maser-hunting-in-the-galactic-plane(efee9222-ec4e-4153-aa6a-4047c08430f9).html.
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The process of massive star formation greatly influences its surroundings through their outflows, vast UV output and shocks from their supernova death. They form at great distances from the Earth, enshrouded by dust and gas and have relatively short lifetimes. Astrophysical masers which form in these environments may act as locators of the star forming regions. The aim of this thesis is to study massive star formation using masers to probe these regions. The three main masers used in this thesis are the Class I and Class II methanol masers and the 6035 MHz ex-OH maser. The methanol masers are divided into two groups, Class I and Class II, based on their distance from a central source. The Class I masers are separated 1-2 pc from a central source, the central source is the star forming region. The Class II masers are associated close to a star forming source. They are often associated with a 6035 MHz ex-OH maser. The 6035 MHz ex-OH masers are less common than the 6668 MHz Class I methanol masers. They are often found at sites of the 6668 MHz Class I masers and 1665/7 MHz OH masers. This thesis presents two maser surveys, the Methanol Multibeam (MMB) survey and the Class I survey. The MMB survey is currently surveying the entire Galactic Plane for the 6668 MHz Class II methanol maser and the 6035 MHz ex-OH maser. Over 60\% of the survey in the Southern hemisphere is now complete using the Parkes telescope. Over 900 6668 MHz Class I methanol masers and 110 6035 MHz ex-OH masers have been detected, with all of these masers pinpoint the location of newly forming high mass stars. Follow up observations to determine the precise locations of the 6668 MHz methanol and 6035 MHz ex-OH masers are currently underway. The first ever unbiased Class I survey has observed 1 sq degree of the Galactic Plane for the 44 GHz Class I methanol masers using the Mopra telescope in Australia. The 44 GHz Class II methanol masers are hypothesised to be associated with the outflows of high mass stellar objects. The Class I survey has detected 25 44 GHz methanol masers, with 23 being new detections. A smaller survey for 36 GHz Class I masers was also conducted using the Mopra telescope centered on the region with the highest population of 44 GHz Class I masers.
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Smilgys, Romas. "Formation of stars and stellar clusters in galactic environment." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/13229.
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Star and stellar cluster formation in spiral galaxies is one of the biggest questions of astrophysics. In this thesis, I study how star formation, and the formation of stellar clusters, proceeds using SPH simulations. These simulations model a region of 400 pc and 107 solar masses. Star formation is modelled through the use of sink particles which represent small groups of stars. Star formation occurs in high density regions, created by galactic spiral arm passage. The spiral shock compresses the gas and generates high density regions. Once these regions attain sufficiently high density, self-gravity becomes dominant and drives collapse and star formation. The regions fragment hierarchically, forming local small groups of stars. These fall together to form clusters, which grow through subsequent mergers and large scale gas infall. As the individual star formation occurs over large distances before forming a stellar cluster, this process can result in significant age spreads of 1-2 Myrs. One protocluster is found to fail to merge due to the large scale tidal forces from the nearby regions, and instead expands forming a dispersed population of young stars such as an OB association.
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Bailin, Jeremy. "Alignment of galactic components in models of galaxy formation." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280672.
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In this thesis, we study the relationship between the angular momentum and shape of galactic disks, satellite galaxies, dark matter halos, and large scale structure using N-body simulations in the context of current models of galaxy formation. In warped galactic disks, the angular momenta of the inner and outer disk are misaligned. We have calculated the torques a misaligned halo imparts on an embedded galactic disk. N-body simulations of disks subject to torques of this strength indicate that the disk tilts in response and develops a trailing warp of the same magnitude as the Milky Way warp. We have investigated whether the warp of the Milky Way's disk is caused by nearby satellite galaxies. The misaligned warp angular momentum is anti-aligned with the orbital angular momentum of the Sgr dSph, and is of the same magnitude. This suggests that Sgr is responsible for the warp. However, N-body simulations of such disk-satellite interactions indicate that the warps excited by Sgr with its current mass and orbit are much smaller than the warp of the Milky Way. The alignment of the shapes and angular momenta of dark matter halos and the large scale environment has been studied in cosmological dark matter simulations. We have analyzed several late snapshots of such a simulation and found rotation of the triaxial figure of the halos. The figure rotates about the minor axis in most cases, at a rate that follows a log-normal distribution centred on Ωp = 0.148 h km s⁻¹ kpc⁻¹. Halos have triaxial shapes that become more spherical at larger radii. The principal axes of individual halos show strong internal alignment, as does the angular momentum, which is usually oriented along the minor axis. This alignment is not perfect, and the median misalignment is large enough to cause galactic warps. The minor axes of halos tend to point perpendicular to filaments and sheets. Major axes show a weaker tendency to point along filaments. These alignments are much stronger for higher mass halos. The angular momenta of galaxy mass halos tend to point along filaments and sheets, while those of group mass halos point perpendicular to the surrounding mass distribution.
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Renda, Agostino. "The formation of stellar halos in late-type galaxies." Swinburne Research Bank, 2007. http://hdl.handle.net/1959.3/34778.
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Thesis (PhD) - Swinburne University of Technology, 2007.Submitted for the degree of Doctor of Philosophy, Swinburne University of Technology - 2007. Typescript. "May 2007". Bibliography: p. 225-237.
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Chamcham, Khalil. "The evolution of galactic discs with a star formation threshold." Thesis, University of Sussex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262321.
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Harding, Paul. "The formation of the Galactic bulge and halo: Observational signatures." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/289743.
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The evolution of tidal debris within the Galactic halo has been simulated to determine its detectability within the constraints imposed by currently available telescopes and instrumentation. Observations of the simulations show that there is a very high probability of detecting and quantifying the presence of tidal debris with a pencil beam survey of 100 square degrees. The debris is readily detectable via the presence of kinematic substructure in the radial velocities. The detection probabilities show surprisingly little change with the age of the debris. Accretion events that occurred up to ≳ 10 Gyr ago can be detected. In the limiting case of a single 10⁷ M(⊙) satellite contributing 1% of the luminous halo mass the detection probability is a few percent using just the velocities of 100 halo stars in a single 1 deg² field. The detection probabilities scale with the accreted fraction of the halo and the number of fields surveyed. Accurate CMDs in the Washington photometric system have been derived for four fields spanning the range of Galactocentric distances from 1.5 to 5.5 kpc. The differential reddening variations within each field were corrected by a new technique optimized for the highly variable reddening variations found in bulge fields. Abundance distributions in the four fields were derived from color-color diagrams in the Washington system. The quality of the photometry which yields photometric abundances with σ[Fe/H] ≲ 0.25 dex (including reddening errors) supplemented by the luminosity information from observations in the 51 filter allows contamination by foreground and background stars to be eliminated from the bulge sample. A clear abundance gradient is seen which is consistent with the change in morphology of the CMDs. The abundance gradient is predominantly due to a decrease in the fraction of stars in the metal-rich shoulder of the abundance distributions. The modal abundance changes little. Relative to Baade's window the magnitude distribution of clump stars in the L354 B-06 field implies a bar angle of ≃ 40 deg.
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Shaw, Martin Anthony. "The luminosity distributions of edge-on spiral and lenticular galaxies." Thesis, University of Edinburgh, 1988. http://hdl.handle.net/1842/27372.
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Minchin, Nigel Robert. "Near-infrared imaging polarimetry of bipolar nebulae." Thesis, University of Hertfordshire, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293286.
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Miceli, Antonino. "LONEOS RR Lyrae stars as probes of galactic structure and formation /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9722.
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Freundlich, Jonathan. "Star formation across cosmic time and its influence on galactic dynamics." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066459/document.
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Les observations montrent qu'il y a dix milliards d'années, les galaxies formaient bien plus d'étoiles qu'aujourd'hui. Comme les étoiles se forment à partir de gaz moléculaire froid, cela signifie que les galaxies disposaient alors d'importants réservoirs de gaz, et c'est ce qui est observé. Mais les processus de formation d'étoiles pourraient aussi avoir été plus efficaces : qu'en est-il ? Les étoiles se forment dans des nuages moléculaires géants liés par leur propre gravité, mais les toutes premières étapes de leur formation demeurent relativement mal connues. Les nuages moléculaires sont eux-mêmes fragmentés en différentes structures, et certains scénarios suggèrent que les filaments interstellaires qui y sont observés aient pu constituer la première étape de la formation des coeurs denses dans lesquels se forment les étoiles. En quelle mesure leur géométrie filamentaire affecte-t-elle les coeurs pré-stellaires ? Des phenomènes de rétroaction liés à l'évolution des étoiles, comme les vents stellaires et les explosions de supernovae, participent à la régulation de la formation d'étoiles et peuvent aussi perturber la distribution de matière noire supposée entourer les galaxies. Cette thèse aborde l'évolution des galaxies et la formation des étoiles suivant trois perspectives : (i) la caractérisation des processus de formation d'étoiles à des échelles sous-galactiques au moment de leur pic de formation ; (ii) la formation des coeurs pré-stellaires dans les structures filamentaires du milieu interstellaire ; et (iii) les effets rétroactifs de la formation et de l'évolution des étoiles sur la distribution de matière noire des galaxiesObservations show that ten billion years ago, galaxies formed their stars at rates up to twenty times higher than now. As stars are formed from cold molecular gas, a high star formation rate means a significant gas supply, and galaxies near the peak epoch of star formation are indeed much more gas-rich than nearby galaxies. Is the decline of the star formation rate mostly driven by the diminishing cold gas reservoir, or are the star formation processes also qualitatively different earlier in the history of the Universe? Ten billion years ago, young galaxies were clumpy and prone to violent gravitational instabilities, which may have contributed to their high star formation rate. Stars indeed form within giant, gravitationally-bound molecular clouds. But the earliest phases of star formation are still poorly understood. Some scenarii suggest the importance of interstellar filamentary structures as a first step towards core and star formation. How would their filamentary geometry affect pre-stellar cores? Feedback mechanisms related to stellar evolution also play an important role in regulating star formation, for example through powerful stellar winds and supernovae explosions which expel some of the gas and can even disturb the dark matter distribution in which each galaxy is assumed to be embedded. This PhD work focuses on three perspectives: (i) star formation near the peak epoch of star formation as seen from observations at sub-galactic scales; (ii) the formation of pre-stellar cores within the filamentary structures of the interstellar medium; and (iii) the effect of feedback processes resulting from star formation and evolution on the dark matter distribution
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Moncelsi, Lorenzo. "BLAST : studying cosmic and Galactic star formation from a stratospheric balloon." Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/13144/.
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Understanding the history of the formation of stars and evolution of galaxies is one of the foremost goals of astrophysics. While stars emit most of their energy at visible and ultraviolet wavelengths, during the early stages of star formation these photons are absorbed by the dusty molecular clouds that host and fuel the emerging stars, and re-emitted as thermal radiation at infrared and submillimeter wavelengths. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) was designed to study the history of obscured star forma- tion in galaxies at cosmological distances and witness the details of the star-formation processes in our own Galaxy, by conducting large- area surveys of the sky at 250, 350, and 500 �m from a long-duration stratospheric balloon platform. Its polarimetric adaptation, BLAST- Pol, will allow us to further probe the strength and morphology of magnetic fields in dust-enshrouded star-forming molecular clouds in our Galaxy. The study of these two diverse, yet highly complemen- tary, topics is the primary scientific motivation for this thesis, which is in two parts. Part One is concerned with the analysis of a combination of the extragalactic dataset collected by BLAST in the 2006 Antarctic cam- paign, which comprises maps containing hundreds of distant, highly dust-obscured, and actively star-forming galaxies, with a wealth of ancillary multi-wavelength data spanning the radio to the ultravio- let. The star-formation rates we observe in massive galaxies at high redshift support downsizing and size evolution. Part Two describes the BLAST-Pol instrument. In particular, we focus on the gondola's primary pointing sensors, the star cameras, and on the design, manufacture and characterization of a polarization IX modulation scheme, comprising a cryogenic achromatic half-wave plate and photolithographed polarizing grids, which has been effectively retrofitted on BLAST-Pol. We report on the construction and deployment of BLAST-Pol, which completed its first successful 9.5-day ight over Antarctica in January 2011 and mapped ten science targets with unprecedented combined mapping speed, sensitivity, and resolution.
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Rawlings, J. I. "Disentangling active galactic nuclei and star formation in extragalactic radio sources." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1425859/.
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This thesis presents a study of the extragalactic radio source population at infrared (IR) and radio wavelengths of the electromagnetic spectrum. The IR/radio emission from these sources can be the result of star−forming processes and/or the result of an accreting supermassive black hole, an active galactic nucleus (AGN). The purpose of this study has been to separate the two different types of emission, determine the dominant process and calculate star formation rates (SFRs) for this population. For the first sample of radio sources, high redshift radio galaxies (HzRGs), polycyclic aromatic hydrocarbon emission has been observed in their mid−IR spectra. For the second sample, the radio sources in the Extended Chandra Deep Field−South (ECDF−S), Herschel photometry was used to infer the contribution of cool dust associated with star formation to the IR emission. Overall, I find that extragalactic radio sources, both those that do and do not contain an AGN, can have a strong component of their IR and/or radio emission from star formation. From this result, I infer they can have exceptional SFRs ("1000sM! yr−1). For the HzRGs, it was also found that they have weak 9.7 μm silicate absorption (!9.7 μm < 0.8). This implies that their mid−IR obscuration is predominantly the result of the dusty torus that surrounds the central engine and not the result of dust in the host galaxy. For the ECDF−S radio sources, AGN and star−forming galaxy contributions to the radio source counts were also determined. I find that sources powered by star formation are responsible for the observed flattening of the counts at "1mJy and a significant portion of these sources host an AGN. The optical morphologies of low−redshift sources are also investigated and Ifind that the faintest sources are mostly either late−type galaxies or irregular/ mergers while the bulk of the bright sources are early−types.
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Utreras, Contreras José. "Studyng the role of galactic rotation on star formation: numerical experiments." Tesis, Universidad de Chile, 2016. http://repositorio.uchile.cl/handle/2250/140026.
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Magíster en Ciencias, Mención AstronomíaEstudiamos la formación estelar y el rol de la rotación a escalas galácticas mediante simulaciones numéricas, utilizando el código de grillas adaptativas Enzo. Parte de este trabajo se centra en estudiar tres leyes de formación estelar encontradas en la literatura: las leyes de Kennicutt-Schmidt y Silk-Elmegreen, y la ecuación dimensionalmente homogénea propuesta por Escala (2015), las que relacionan la formación estelar proyectada con propiedades galácticas. Durante la última década, estudios con un mayor número de observaciones y mayor resolución espacial han puesto en duda que tan fidedignas son las leyes de Kennicutt-Schmidt y Silk-Elmegreen. Para la primera, estudios sugieren la existencia de dos regímenes formación estelar con diferente amplitud y otros proponen un único régimen modificando la forma funcional de la ley de Kennicutt-Schmidt original. Para la ley de Silk-Elmegreen grandes modificaciones no han sido requeridas, sin embargo estudios recientes del momento angular en galaxias han mostrado comportamientos contrarios a esta ley. Estos problemas han motivado el estudio del origen físico de estas relaciones y sus formulaciones matemáticas. Entre estos, Escala (2015) encuentra una función que es capaz de explicar varios observables (de observaciones y simulaciones), dependiendo de los procesos físicos que dominan la dinámica galáctica. En este trabajo estudiamos como las galaxias evolucionan comparándolas con estas leyes, mediante cambios en parámetros físicos, específicamente la rotación galáctica.\\ Realizamos simulaciones de galaxias espirales y discos nucleares de galaxias de formación violenta, constituidas por gas, estrellas y materia oscura. Durante la evolución de estas galaxias el gas puede enfriarse, fragmentarse y formar estrellas que interactúan con el medio interestelar mediante explosiones de supernova. Como condiciones iniciales, mantenemos fija la masa en gas y su distribución radial para cada tipo de galaxia mientras el perfil de rotación es variado. Esto nos permite aislar medianamente el efecto producido por la rotación en la evolución de las galaxias. Los parámetros deformación estelar son elegidos para obtener la bimodalidad observada en la ley de Kennicutt-Schmidt. La naturaleza bi-dimensional de esta ley nos motiva a estudiar las leyes mencionadas desde distintas líneas de visión, permitiéndonos probar como estas capturan la naturaleza tridimensional de la formación estelar. Nuestras simulaciones muestran ser bien representadas por las leyes de Kennicutt-Schmidt y Silk-Elmegreen globalmente. Sin embargo, encontramos una anti-correlación entre la eficiencia de formación estelar y la velocidad angular Ω, que no es considerada en estas leyes. Incluyendo los efectos de la inclinación respecto al observador, las simulaciones muestran menores tiempos de consumo de gas en la relación de Kennicutt-Schmidt y tiempos similares en la ley de Silk-Elmegreen, atribuido a efectos geométricos. La ecuación propuesta por Escala (2015) describe la evolución de las simulaciones con menor dispersión que las relaciones anteriores. Bajo esta formulación, diferentes inclinaciones muestran eficiencias similares, debido a que considera la concentración de gas en la línea de visión. Sin embargo, esta relación aún muestra la anti-correlación ya mencionada. Estudiamos esta anti-correlación y encontramos que la eficiencia de formación estelar decrece exponencialmente con la velocidad angular en ambos tipos de galaxia. Requiriendo que la eficiencia sea función de cantidades adimensionales, introducimos el parámetro de tiempo de caída libre inicial τ, encontrando que la eficiencia puede ser descrita por una función exponencial decreciente de Ωτ. Este resultado nos entrega una formación estelar que toma en cuenta la concentración de gas en la línea de visión y variaciones en la velocidad angular.
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Westmoquette, M. S. "Super star clusters, their environment, and the formation of galactic winds." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1446265/.
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Starbursts and starburst-driven outflows play a central role in the evolution of galaxies. However, the paucity of detailed observations of superwinds limits our current understanding of these complex systems. To this end we have undertaken two intensive ground- and space-based observing campaigns aimed at studying the ionized gas conditions in two nearby starburst galaxies, M82 and NGC 1569. These two systems host starbursts on different scales: M82 contains densely-packed star cluster complexes that drive a large-scale bipolar superwind, whereas NGC 1569 exhibits a set of discrete superbubbles powered by only a handful of young massive clusters. We have used long-slit spectra, obtained with the Hubble Space Telescope (HST), together with HST and ground-based imaging from the WIYN 3.5 m telescope, to observe M82 at optical wavelengths. The high quality HST spectroscopy obtained with the Space Telescope Imaging Spectrograph (STIS), have allowed us to investigate the properties of the gas across the starburst core. By combining high-resolution HST imaging with deep WIYN observations, we have created the most comprehensive image of the M82 superwind to date, and used it to characterise the outflow morphology. We also observed the centre of NGC 1569 with the Integral Field Unit (IFU) of the Gemini Multi-Object Spectrograph (GMOS) on the Gemini-North telescope, and M82 with the WIYN/DensePak and SparsePak IFUs. We decomposed the observed emission-line profile shapes, and identified an underlying broad ( > 100 kms-1) component across the starburst cores of both galaxies. By mapping the spatial variation of each individual line component, we have developed a new model to explain the broad emission and the state of the interstellar medium (ISM) in the central starbursts. We have also observed the outer-wind environment of NGC 1569 with the WIYN SparsePak instrument. We find that the broad line is only found within 500-700 pc of the centre, and speculate that the boundary of this region may indicate the point at which bulk motions begin to dominate over turbulence.
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Stonkutė, Edita. "Chemical composition of kinematically identified galactic stellar group." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130925_093107-33619.
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A number of stellar streams, moving and kinematic groups were identified in the Milky Way galaxy. Some of them are suspected to originate from accreted satellites. Can we also find such traces of ancient merger events in the solar neighbourhood? Helmi et al. (2006) identified three new coherent groups of stars in the Geneva-Copenhagen survey (Nordström et al. 2004) and suggested that those might correspond to remains of disrupted satellites.
With the detailed chemical composition analysis of the newly identified kinematic group we aim to contribute to the Galactic substructure studies. The main aim of the study is to perform a high-resolution spectroscopic elemental abundance analysis in stars belonging to one of the newly identified kinematic groups and to compare the results with other stars in the Galactic disc.
We performed the detailed chemical analysis of 21 stars attributed to Group 3 of the Geneva-Copenhagen survey and six comparison Galactic thin disc stars. The main atmospheric parameters and abundances of 22 chemical elements were determined. All programme stars are overabundant in oxygen and α-elements compared with the Galactic thin-disc. This abundance pattern has similar characteristics to those of the Galactic thick disc. The abundances of chemical elements produced predominantly by the r-process are overabundant in comparison with Galactic thin-disc dwarfs of the same metallicity. The abundances of iron-group elements and chemical elements produced mainly... [to full text]Paukščių Tako galaktikoje yra identifikuota žvaigždžių srautų, judančių bei kinematinių grupių, kurių kilmė siejama su įkritusiomis galaktikomis. Aktualu ištirti, ar yra tokių senųjų substruktūrų pėdsakų mūsų Saulės aplinkoje? Helmi ir kt. (2006), panaudoję Nordström ir kt. (2004) Ženevos–Kopenhagos apžvalgos (ŽKA) katalogą, identifikavo tris naujas koherentines žvaigždžių grupes, kurios pasižymi išskirtiniais kinematiniais parametrais ir gali būti užgalaktinės kilmės. Šiuo disertacijos darbu siekiama prisidėti prie Galaktikos substruktūrų tyrimų, nustatant detalią cheminę vienos iš Helmi ir kt. identifikuotų žvaigždžių grupių sudėtį. Svarbu išsiaiškinant, ar ŽKA kinematinės grupės žvaigždžių atmosferų cheminė sudėtis skiriasi nuo Galaktikos disko žvaigždžių. Nustatėme 21 3–osios ŽKA kinematinės grupės bei 6 palyginamųjų plonojo disko žvaigždžių atmosferų pagrindinius parametrus bei 22 cheminių elementų gausas. Kinematinės žvaigždžių grupės deguonies ir α–elementų gausos yra padidėjusios lyginant su plonuoju disku ir yra panašios į storojo disko. Cheminių elementų, daugiausia pagaminamų s–procese, gausos ir geležies grupės elementų gausos yra panašios į to paties metalingumo plonojo disko nykštukių cheminių elementų gausas, o cheminių elementų, daugiausia pagaminamų r–procese, gausos yra padidėjusios lyginant su plonuoju disku. Panaši cheminė tirtos kinematinės grupės bei storojo Galaktikos disko sudėtis rodo, kad kinematinės žvaigždžių grupės ir storojo disko žvaigždžių... [toliau žr. visą tekstą]
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Marsden, Gaelen. "Observing the galactic plane with the Balloon-borne Large-Aperture Submillimeter Telescope." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/205.
Full textAbstract:
Stars form from collapsing massive clouds of gas and dust. The UV and optical light emitted by a forming or recently-formed star is absorbed by the surrounding cloud and is re-radiated thermally at infrared and
submillimetre wavelengths. Observations in the submillimetre spectrum are uniquely sensitive to star formation in the early Universe, as the peak of the thermal emission is redshifted to submillimetre wavelengths. The coolest objects in star forming regions in our own Galaxy, including heavily-obscured proto-stars and starless gravitationally-bound clumps, are also uniquely bright in the submillimetre spectrum. The Earth's atmosphere is mostly opaque at these wavelengths, however, limiting the spectral coverage and sensitivity achievable from ground-based observatories.
The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) observes the sky from an altitude of 40 km, above 99.5% of the atmosphere, using a long-duration scientific balloon platform. BLAST observes at 3 broad-band wavelengths spanning 250-500 micron, taking advantage of detector technology developed for the space-based
instrument SPIRE, scheduled for launch in 2008. The greatly-enhanced atmospheric transmission at float altitudes, increased detector sensitivity and large number of detector elements allow BLAST to survey much larger fields in a much smaller time than can be accomplished with ground-based instruments. It is expected that in a
single 10-day flight, BLAST will detect ~10000 extragalactic sources, ~100 times the number detected in 10 years of ground-based observations, and 1000s of Galactic star-forming sources, a large fraction of which are not seen by infrared telescopes.
The instrument has performed 2 scientific flights, in the summer of 2005 and winter of 2006, for a total of 16 days of observing time. This thesis discusses the design of the instrument, performance of the flights, and presents the analysis of 2 of the fields observed during the first flight. A failure in the optical system during the first
flight precluded sensitive extragalactic observations, so the majority of the flight was spent observing Galactic targets. We anticipate exciting extragalactic and Galactic results from the 2006 data.
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Falder, James Thomas. "The environments of high redshift active Galactic nuclei." Thesis, University of Hertfordshire, 2012. http://hdl.handle.net/2299/8960.
Full textAbstract:
In this thesis I study the links between Active Galactic Nuclei (AGN) and their surrounding large scale environments mainly at high redshift. I firstly use Spitzer space telescope data for one of the largest and most uniformly selected samples of radio-loud and radio-quiet AGN at high redshift. It consists of 173 AGN of both type-1 Sloan Digital Sky Survey (SDSS) Quasi- Stellar-Objects (QSOs) and type-2 radio-galaxies at the single cosmic epoch of z ∼ 1. I find significant (8 σ) over-densities of galaxies in the AGNs’ environments when compared to an offset field. Further to this I address the question of whether radio-loud AGN are found, on average, in denser environments than their radio-quiet counterparts. I show that there is a link between the environment and radio luminosity of the most powerful radioloud QSOs and RGs in the sample, and also reconcile the conflicting results in the literature by suggesting that there is only a link to the environment at the highest radio powers. I extend this work to higher redshift with data from the Spitzer extragalactic Representative Volume Survey (SERVS) and type-1 SDSS QSOs in the regions covered by SERVS. This deep data allowed me to study the environments of QSOs in the redshift range 1 < z < 4. Again I find significant (4 σ) over-densities of galaxies around the QSOs in this sample, this time making use of the 3.6-4.5 μm colour to select galaxies more likely to reside at the redshifts of interest. I show that the environments of these QSOs are comparable to those predicted for similarly large black holes in the Durham semi-analytic galaxy formation model (Galform). Finally I use data from the Herschel-Astrophysical Terahertz Large Area Survey with the recently launched Herschel space observatory to study the environments of type-1 QSOs in the far-infrared (FIR). I find a small excess of galaxies around the QSOs for which I find that the star-formation rate increases with increasing redshift. The star-formation rates are estimated by modelling the FIR spectral energy distribution of the galaxies with a modified black-body spectrum. This follows the general increase in starformation rate with redshift observed in the Universe as a whole. I also compare these findings with those made by the Submillimeter Common-User Bolometer Array (SCUBA) of higher redshift QSOs.
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Augustin, Ramona. "Characterising the circum-galactic medium : observations in absorption and simulations of emission." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0254.
Full textAbstract:
Comprendre les processus de flux de gaz entrant et sortant des galaxies est crucial pour les études de l’évolution des galaxies. Cependant, l’observation du médium circum-galactique (CGM) faible et diffus, où se déroulent ces processus, reste difficile. Dans ce travail, j’explore différentes méthodes pour observer, simuler et caractériser le gaz autour des galaxies dans le CGM. J'ai identifié et caractérisé des homologues de galaxie aux systèmes lorentziens (DLA) à z équivalent 1 en utilisant des observations au télescope spatial de Hubble (HS) hautement résolues spatialement. Je détermine leurs masses stellaires et constate que les galaxies sont généralement moins massives que la population moyenne des galaxies, mais suivent les tendances prédites en termes de taux de formation d'étoiles et de métallicité. La haute résolution spatiale des données optiques HST permet également de mieux regarder la morphologie de ces galaxies et de révéler des structures complexes et inattendues. Pour cartographier le CGM nous avons besoin d’observations en émission. Pour améliorer les stratégies d’observation du CGM en émission, j’ai calculé des prédictions à partir de simulations de zoom cosmologique dédiées, post-traitées avec un modèle d'émission du code CLOUDY. Cette combinaison permet de créer des cubes de données de type galaxie halo de type IFU simulés qui sont ensuite utilisés comme entrées dans les modèles d’instruments afin de préparer les observations CGM avec FIREBall-2 (spectrographe UV sur ballon) et HARMONI (IFU proche infrarouge sur l’ELT). Je trouve que FIREBall-2 est capable de détecter Ly alpha et que HARMONI est compétitif pour les études CGMUnderstanding the processes of gas flows in and out of galaxies is crucial in galaxy evolution studies. Yet, observations of the faint and diffuse Circum-Galactic Medium (CGM), where these processes take place, remain challenging. In this work, I explore different methods to observe, simulate and characterise the gas around galaxies in the CGM. I identified and characterised galaxy counterparts to Damped Lyman-alpha Absorbers (DLAs) at z equivalent 1 using highly spatially resolved Hubble Space Telescope (HST) observations. I determine their stellar masses and find that the galaxies are generally less massive than the average galaxy population, but follow the predicted trends in terms of star formation rate and metallicity. The high spatial resolution of the optical HST data also allows for a closer look at the morphology at those galaxies and reveals complex, unexpected structures. While absorption lets us investigate very faint gas, it is usually limited to a single line of sight and we need observations in emission to map the CGM and gain information on its extent and clumpiness. To improve observing strategies of the CGM in emission, I make predictions from dedicated cosmological zoom-in simulations, post-processed with a CLOUDY emission model. This combination allows to create mock IFU-like galaxy halo data cubes which are next used as input to instrument models in order to prepare CGM observations with FIREBall-2 (UV spectrograph on a balloon) and HARMONI (near-infrared IFU on the ELT). I predict that FIREBall-2 is capable of detecting Ly alpha and find HARMONI to be competitive for CGM studies
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Iliev, Ilian Tzankov. "The equilibrium structure of cosmological halos and the effects of feedback on cosmological structure formation /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
Full text
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Majewski, Steven R., Ricardo P. Schiavon, Peter M. Frinchaboy, Carlos Allende Prieto, Robert Barkhouser, Dmitry Bizyaev, Basil Blank, et al. "The Apache Point Observatory Galactic Evolution Experiment (APOGEE)." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625493.
Full textAbstract:
The Apache Point Observatory Galactic Evolution Experiment (APOGEE), one of the programs in the Sloan Digital Sky Survey III (SDSS-III), has now completed its systematic, homogeneous spectroscopic survey sampling all major populations of the Milky Way. After a three-year observing campaign on the Sloan 2.5 m Telescope, APOGEE has collected a half million high-resolution (R similar to 22,500), high signal-to-noise ratio (>100), infrared (1.51-1.70 mu m) spectra for 146,000 stars, with time series information via repeat visits to most of these stars. This paper describes the motivations for the survey and its overall design-hardware, field placement, target selection, operations-and gives an overview of these aspects as well as the data reduction, analysis, and products. An index is also given to the complement of technical papers that describe various critical survey components in detail. Finally, we discuss the achieved survey performance and illustrate the variety of potential uses of the data products by way of a number of science demonstrations, which span from time series analysis of stellar spectral variations and radial velocity variations from stellar companions, to spatial maps of kinematics, metallicity, and abundance patterns across the Galaxy and as a function of age, to new views of the interstellar medium, the chemistry of star clusters, and the discovery of rare stellar species. As part of SDSS-III Data Release 12 and later releases, all of the APOGEE data products are publicly available.
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Rey, Raposo Ramon. "The interplay between stellar feedback and galactic environment in molecular clouds." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/21022.
Full textAbstract:
In this thesis we address the problem of understanding the star formation process in giant molecular clouds in a galactic context. Most simulations of molecular clouds to date use an oversimplified set of initial conditions (turbulent spheres/boxes or colliding flows). Full galactic scale models are able to generate molecular clouds with complex morphologies and velocity fields but they fail to reproduce in detail the effects that occur at sub-pc scales (e.g. stellar feedback). Our goal is to build the bridge between these two scenarios, and to model the star formation process in molecular clouds produced in a galactic context. We extract our molecular clouds from full-scale galactic simulations, hence we need to increase the resolution by two orders of magnitude. We introduce the details of the program used to simulate molecular clouds in Chapter 2, and describe in detail the method we follow to increase the resolution of the galactic clouds. In Chapter 3 we compare our simulated galactic clouds with the more conventional approach of using turbulent spheres. We create turbulent spheres to match the virial state of three galactic clouds. We perform isothermal simulations and find that the velocity field inherited from the full-scale galactic simulations plays an important role in the star formation process. Clouds affected by strong galactic shear produce less stars compared with clouds that are compressed. We define (and test) a set of parameters to characterise the dynamical state of our clouds. To include stellar feedback in our simulations we need to introduce a cooling/heating algorithm. In Chapter 4 we analyse how the different velocity fields of our clouds change the temperature distribution even in the absence of feedback. To study the formation of molecules we need to model the chemistry of H2 in our clouds. We also add CO chemistry, and produce synthetic observations of our clouds. The effect of feedback from winds and supernovae in galactic clouds is studied in Chapter 5. We analyse the effect of winds in clouds with very different velocity fields. We find that the effect of winds is stronger in highly virialised, high star forming clouds, with clouds with weak galactic shear, compared to unbound shear-dominated clouds. The steady and continuous action of the winds appears to have a greater effect than the supernovae. In summary, the inherited properties from the galaxy have an impact on many relevant processes in star formation, influencing gravitational collapse, the formation of filamentary structures, the temperature field of the cloud, and have a considerable effect on the impact of feedback in the clouds.
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Duong, Ly. "Unravelling the evolution of the Galactic stellar disk and bulge." Phd thesis, Canberra, ACT : The Australian National University, 2018. http://hdl.handle.net/1885/149502.
Full textAbstract:
The formation and evolution of spiral galaxies is a research
topic central to modern Astronomy. In this context, the Milky Way
offers a unique opportunity for astronomers to study a spiral
galaxy in detail and thus informs many aspects of galaxy
formation theory.
The observational signatures of Galactic stellar components
provide clues to its assembly history. This thesis is focused on
two main components of the Galaxy: the stellar disk and bulge. In
particular, we examine the chemical properties of these
components and their implications for Galactic evolution. The
data in this thesis were obtained with HERMES, a new
high-resolution optical spectrograph on the Anglo Australian
Telescope. The disk sample consists of over 3000 giant-branch
stars, extending up to 4 kpc in height from the Galactic plane.
The thin disk (low-α population) exhibits a steep negative
vertical metallicity gradient, a signature observed in galaxy
evolution models where radial migration plays an important role.
The thick disk (high-α population) has a weaker vertical
metallicity gradient, which could have arisen from a settling
phase of the primordial disk. The [α/Fe] ratios of the thin and
thick disk populations are distinct and nearly constant with
height. This indicates the two populations were formed in very
different conditions, and although the high-α population likely
experienced a settling phase, its formation timescale was fast
still, in the order of a few Gyrs.
To investigate the chemistry of the Galactic bulge and its
connection to the disk, we obtained abundance ratios of 18
elements for more than 800 red giants. The [α/Fe] abundance
ratios show vertical variations that are consistent with the
distribution of bulge metallicity components: at high latitudes
[α/Fe] is enhanced as the metal-poor component dominates; closer
to the plane, the metal-rich components contribute lower [α/Fe].
However, at fixed metallicity, all elements show uniform
abundance ratios with latitude. We observe normal [Na/Fe] ratios
that do not vary as a function of latitude at fixed metallicity,
indicating that the bulge does not contain strongly
helium-enhanced populations as observed in globular clusters.
By comparing our results with that of the GALAH survey, we
conclude that there are similarities between the bulge and disk
in terms of their chemistry. However, the more metal-poor bulge
population ([Fe/H] ≲ -0.8) shows enhanced abundance ratios
compared to the disk for some light, alpha, and iron-peak
elements that are associated with
core-collapse supernovae (SNeII). This population may have
experienced a different evolution to bulge stars of disk origin.
Moreover, the [La/Eu] abundance ratios suggest higher r-process
contribution in the bulge, which indicates that overall the bulge
experienced a higher star formation rate than the disk.
Keywords: Galaxy, stellar populations, stellar abundances, disk,
bulge, galaxy formation, galaxy evolution
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Green, James Andrew. "Studying high-mass star formation & galactic structure through the methanol multibeam survey." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491493.
Full textAbstract:
This thesis presents the techniques and procedures that enable a new Galactic plane survey for 6668-MHz methanol masers, exclusive signposts of high-mass star formation. The statistics and properties of the largest ever sample of 6668MHz methanol masers arc detailed, including completeness and total population estimates. Through the application of rotation curves the distances are found, which then facilitates establishing the Galactic distribution of these masers, and thus of high-mass star formation regions. The relationship between these and the Spiral arms is examined. The most accurate luminosity distribution of 6668MHz methanol masers in the Galaxy and the Large Magellanic Cloud are given, together with new detections of 6668-MHz methanol and 6035-MHz hydroxyl masers in the Large Magellanic Cloud. A high spatial resolution study of an individual massive star formation region, aNI, is also presented, which not only details the precise structure and relation of methanol and excited-state hydroxyl to other species of masers for the first time, but also presents the first tentative detection of Zeeman splitting in a 6668-MHz methanol maser.
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Becerra, Saavedra Fernando Felipe. "A study of galactic star formation and massive black hole growth through simulations." Tesis, Universidad de Chile, 2012. http://www.repositorio.uchile.cl/handle/2250/112012.
Full textAbstract:
Magíster en Ciencias, Mención AstronomíaEstudiamos la formación estelar en escalas galácticas y el crecimiento de agujeros negros a través de simulaciones usando el código de grilla adaptativa de refinamiento Enzo. Nuestro estudio se centra en dos de las más famosas leyes de formación estelar: las ley de Kennicutt-Schmidt y la ley de Silk, ambas relacionan la tasa de formación estelar con propiedades globales de la galaxia. A pesar de que ambas han cuantificado exitosamente esta relación, aún no hay un consenso en el valor exacto de sus pendientes. Nosotros tratamos de clarificar este problema estudiando los factores que influyen en ambas leyes, tales como la densidad de gas superficial, el tiempo orbital y la masa rotacional. Para estudiar el crecimiento de agujeros negros masivos, centramos nuestro trabajo en las relaciones $M_{BH}-M_{bulge}$ y $M_{BH}-\sigma$, las cuales relacionan la masa de un agujero negro con propiedades globales de su galaxia huésped. Tratamos de explicar el origen de ambas relaciones a través de un análisis del Medio Interestelar. Modelamos galaxias locales con tres componentes: gas, estrellas y materia oscura. Dejamos a los modelos evolucionar por 1 Gyr, y durante la evolución el gas puede formar estrellas, las cuales mueren en forma de supernovas. Al final de las corridas, nuestras simulaciones están caracterizadas por un medio altamente turbulento y compresible, con una Función de Densidad de Probabilidades que puede ser ajustada por una distribución lognormal a altas densidades. Su espectro de potencia de velocidad es bien ajustado por una ley de potencia de pendiente ~-4 en el espacio k a escalas pequeñas, lo cual es más pronunciado que la turbulencia de Kolmogorov y la de Burger. Este espectro de potencia nos permite deducir una relación del tipo $v_r \sim v_{rot} \left( \lambda \over R_d \right)^{-\beta}$, la cual es el nexo necesario entre las propiedades globales de la galaxia y la alimentación del agujero negro masivo central. Estudiamos la eficiencia de formación estelar en nuestras galaxias, donde investigamos cómo la pendiente de las leyes de Kennicutt-Schmidt y Silk pueden variar dependiendo de cómo definamos las cantidades involucradas en ambas leyes. Las dos leyes son fuertemente dependientes en el criterio ocupado para seleccionar el radio al cual se calculan las densidades superficiales, y el intervalo de tiempo ocupado para medir la tasa de formación estelar. En el primer caso la elección de un radio más grande puede llevar a obtener menores pendientes, mientras que en el segundo caso las pendientes más bajas son obtenidas usando un intervalo de tiempo más grande para promediar las tasas de formación estelar. Ambos efectos pueden cambiar la pendiente de las leyes de formación estelar en el rango entre 0.8 y 2.1. Nuestras simulaciones también muestran una dependencia en los perfiles iniciales de $M_{rot}$. Esta relación es más pronunciada al comienzo de las simulaciones, donde la masa rotacional determina el tiempo al cual las galaxias comienzan a formar estrellas, y por lo tanto determina las tasas de formación estelar en etapas tempranas de la evolución.
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Malefahlo, Eliab. "Measuring the quasar luminosity function below the detection threshold." University of the Western Cape, 2016. http://hdl.handle.net/11394/4956.
Full textAbstract:
>Magister Scientiae - MScThe radio emission of radio-quiet active galactic nuclei (AGN) is thought to be from star formation and AGN related emission. I investigate these sources using 1.4 GHz radio data from FIRST and three optical quasars samples from the SDSS: (i) a volume-limited sample in the redshift range 0:2 < z < 0:4 defined by Mi < -23 (ii) magnitude-limited sample in the redshift range 1:8 < z < 2:5 defined by mr ≤ 18:5 and (iii) a uniform sample in the redshift range 0:2 < z < 3:5 (divided into 12 redshift bins). I constructed radio source counts and radio luminosity functions (RLFs) using the optical quasars detected in FIRST, which are consistent with literature results obtained using SDSS and NVSS quasars. There are differences at the low uxs end because of the different resolutions of FIRST and NVSS. I applied a median stack method to the 12 redshift bins of the uniform sample and found that the median ux decreases from 182 µJy in the lowest redshift bin to 39 µJy and the highest redshift bin. This is because the high redshift quasars although more luminous than their low redshift counterparts, they are much further away so they have lower uxes. I probed the quasar radio source counts to lower levels using reconstructed source counts obtained by applying the Bayesian stack technique. The reconstructed radio source counts were then used to constructed the quasar RLF to lower levels, where I found: (i) for z < 1 the constructed quasar RLF has the same slope as the detected quasars, suggesting that like the detect quasars their radio emission is dominated by AGN related emission (ii) above z = 1 the constructed RLF steepens with redshift, which suggests the strong link between accretion rate and radio jet power is gradually breaking down towards faint optical luminosities at high redshift.
National Astrophysics and Space Science Program (NASSP) and SKA Africa
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Xu, Lei. "The Relation between Luminous Active Nuclei and Star Formation in Their Host Galaxies." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/312746.
Full textAbstract:
Studies of central black holes (BHs) in nearby galaxies revealed tight correlation between the BH mass the host galaxy bulge mass, indicating a link between BH and star formation (SF) in the host galaxy. Luminous active galactic nuclei (AGN) are powered by mass accretion onto supermassive BHs. Observations of the AGNs and the SF in their host galaxies are required to understand their relation and how they establish this BH mass-galaxy bulge mass correlation over a wide range of cosmic lookback times. This thesis presents a survey of 24 μm-selected luminous AGN and their host galaxies up to z ~ 3.2. It focuses on the foreground and background broad line (Type-1) and narrow line (Type-2) AGNs of 30 massive galaxy cluster fields with total survey area of 5.2 deg², using the multi-wavelength dataset from the ultraviolet (UV) to far infrared (FIR) from the Local Cluster Substructure Survey. The AGN sample is nearly complete to a 1 mJy flux cutoff at 24 μm, and is optical-spectroscopically identified. With this dataset and the accompanying MMT/Hectospec spectroscopy survey, the properties of AGNs such as BH masses, BH accretion rates, and total luminosities, can be readily determined. Particularly, the Herschel data (100, 160, 250, 350, and 500 μm) sample the FIR peak of sources in our sample, and provide constraints on the star formation rates (SFR) in the host galaxies. For the Type 1 AGN sample, most of the systems are at z > 0.6 with luminosities > 10^45 ergs/s. Out of the 205 Type-1 AGNs, 107 are detected in at least two Herschel bands. We use AGN, stellar, and SF galaxy templates to decompose their spectral energy distributions (SEDs) from the UV to the FIR, and estimate their IR SF luminosities, AGN luminosities, and their host galaxy stellar masses. The SED decomposition reveals that a high level of SF is ubiquitous for our 24 μm-selected Type-1 AGN sample. For sources at z < 1, the stellar components from SED decomposition provide direct constraints on the stellar mass. For sources at z > 1, the BH mass-bulge stellar mass correlation is used for indirect constraints on the stellar mass. We carried out a similar analysis on the 85 Type-2 AGNs and their host galaxies up to z ~ 0.8, out of which 55 are detected in at least two Herschel bands. We reach the same conclusion as for the Type 1 AGN sample. That is, 1) These AGN host galaxies are very massive, and the vast majority of these galaxies have specific star formation rates (SSFR) consistent with those of main-sequence, star-forming galaxies rather than starbursting galaxies; 2) Most of these AGNs accrete at a rate close to 10% of Eddington; 3) We also find a strong correlation between the IR luminosity of the SF component and the AGN total luminosity, for both Type 1 and Type 2 AGNs. However, we show that the correlation could arise just because the BH mass (and hence AGN total luminosity) and the SF are both correlated with the galaxy mass, rather than requiring a causal connection between the observed rates of SF and the nuclear activity.
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Nelson, Erica June. "The Spatial Distribution of Star Formation in Galaxies| Observing the Emergence of Galactic Structure." Thesis, Yale University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10160870.
Full textAbstract:
A high resolution measurement of the distribution of star formation within galaxies is key to understanding the emergence of galactic structure. The aim of this thesis is to understand how the structure of galaxies is built by developing a new method to spatially resolve their star formation. Using Ha maps for 2676 galaxies, this thesis shows where star formation is distributed in galaxies during the epoch 0.7 < z < 1.5 when a third of the total star formation in the history of the universe occurred. Across the star formation rate - stellar mass plane (the "main sequence"), star formation is `spatially coherent': in galaxies with higher than average star formation rates, Ha is enhanced throughout the disk; similarly, in galaxies with low star formation rates Ha is depressed throughout the disk. This places constraints both on the mechanisms for enhancing and quenching star formation as well as on how the structure of galaxies is built. The disk scale length of star formation in galaxies is larger than that of the stars, a direct demonstration that the disks of galaxies grow inside-out. While most star formation in most galaxies occurs in disks, not all of it does. With the first spatially resolved measurement of the Balmer decrement at z > 1, it can be seen that galaxies with M* > 1010M[special characters omitted] have significant dust attenuation toward their centers. This means that we are witnessing the build-up of the dense stellar cores of massive galaxies through dust-obscured in-situ star formation. The most massive galaxies are thought to have formed their dense stellar cores at even earlier cosmic epochs. This thesis presents the first confirmed example of a massive galaxy core in the process of formation at z = 2.3. It has one of the highest velocity dispersions ever measured for a normal star forming galaxy and also appears to be building through very dense, dust-enshrouded star formation.
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Massari, Davide <1987>. "COSMIC-LAB: Terzan 5 as a fossil remnant of the Galactic bulge formation epoch." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6731/1/Massari_Davide_tesi.pdf.
Full textAbstract:
The formation and evolution of galaxy bulges is a greatly debated topic in modern astrophysics.
An approach to address this issue is to look at the Galactic bulge, the closest to us.
According to some theoretical models, our bulge built-up from the merger of substructures formed from the instability and fragmentation of a proto-disk in the early phases of Galactic evolution.
We may have discovered the remnant of one of these substructures: the stellar system Terzan 5.
Terzan 5 hosts two stellar populations with different iron abundances, thus suggesting it once was far more massive than today. Moreover, its peculiar chemistry resembles that observed only in the Galactic bulge.
In this Thesis we perform a detailed photometric and spectroscopic analysis of this cluster to determine its formation and evolutionary histories. Form the photometric point of view we built a high-resolution differential reddening map in Terzan 5 direction and we measured relative proper motions to separate its member population from the contaminating field stars. This information represents the necessary work to measure the absolute ages of Terzan 5 populations via the Turn-off luminosity method.
From the spectroscopic point of view we measured abundances for more than 600 stars belonging to Terzan 5 and its surroundings in order to build the largest field-decontaminated metallicity distribution for this system.
We find that the metallicity distribution is extremely wide (more than 1 dex) and we discovered a third, metal-poor and alpha-enhanced population with average [Fe/H]=-0.8.
The striking similarity between Terzan 5 and the bulge in terms of their chemical formation and evolution revealed by this Thesis suggests that Terzan 5 formed in situ with the bulge itself. In particular its metal-poor populations trace the early stages of the bulge formation, while its most metal-rich component contains crucial information on the bulge more recent evolution.
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Massari, Davide <1987>. "COSMIC-LAB: Terzan 5 as a fossil remnant of the Galactic bulge formation epoch." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6731/.
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The formation and evolution of galaxy bulges is a greatly debated topic in modern astrophysics.
An approach to address this issue is to look at the Galactic bulge, the closest to us.
According to some theoretical models, our bulge built-up from the merger of substructures formed from the instability and fragmentation of a proto-disk in the early phases of Galactic evolution.
We may have discovered the remnant of one of these substructures: the stellar system Terzan 5.
Terzan 5 hosts two stellar populations with different iron abundances, thus suggesting it once was far more massive than today. Moreover, its peculiar chemistry resembles that observed only in the Galactic bulge.
In this Thesis we perform a detailed photometric and spectroscopic analysis of this cluster to determine its formation and evolutionary histories. Form the photometric point of view we built a high-resolution differential reddening map in Terzan 5 direction and we measured relative proper motions to separate its member population from the contaminating field stars. This information represents the necessary work to measure the absolute ages of Terzan 5 populations via the Turn-off luminosity method.
From the spectroscopic point of view we measured abundances for more than 600 stars belonging to Terzan 5 and its surroundings in order to build the largest field-decontaminated metallicity distribution for this system.
We find that the metallicity distribution is extremely wide (more than 1 dex) and we discovered a third, metal-poor and alpha-enhanced population with average [Fe/H]=-0.8.
The striking similarity between Terzan 5 and the bulge in terms of their chemical formation and evolution revealed by this Thesis suggests that Terzan 5 formed in situ with the bulge itself. In particular its metal-poor populations trace the early stages of the bulge formation, while its most metal-rich component contains crucial information on the bulge more recent evolution.
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Ragan, Sarah E. "Peering into the heart of galactic star formation : a detailed characterization of infrared-dark clouds /." [S.l. :] University of Michigan, 2009. http://adsabs.harvard.edu/abs/2009PhDT........12R.
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Stanley, Flora. "Far-infrared constraints on the ongoing star formation of distant galaxies hosting active galactic nuclei." Thesis, Durham University, 2016. http://etheses.dur.ac.uk/11741/.
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There have been a multitude of observational findings supporting a co-evolution of the central BH and its host galaxy. This co-evolution is expected to be driven by a connection between the two growing mechanisms of active galactic nuclei (AGN; accretion onto the central super-massive black hole), and star formation. In an effort to find more direct evidence for a connection between the two mechanisms of AGN and star formation I investigate the star formation rates (SFRs) of galaxies hosting X-ray, optical, and radio AGN. For the analysis of these samples I have developed methods to calculate the mean and individual SFRs of distant AGN and improve on previous work by simultaneously taking into account redshift and mass when interpreting the results. I use infrared photometry from WISE, Spitzer and Herschel to decompose the infrared (IR) spectral en- ergy distributions (SEDs) into AGN and star formation components and undertake careful treatment of the upper limits in the SED analyses and average SFR calculations. Using these methods I have calculated the mean SFRs of ~2000 X-ray and ∼3000 optically selected AGN spanning the AGN luminosity range of 10^43
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Sharma, Sanjib. "Numerical Simulations of Galaxy Formation: Angular Momentum Distribution and Phase Space Structure of Galactic Halos." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1413%5F1%5Fm.pdf&type=application/pdf.
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Butterfield, Natalie. "Kinematics and evolution of massive star formation in the central molecular zone of the galactic center." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6382.
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The environmental conditions in the center of the Milky Way galaxy (Central Molecular Zone; CMZ) are much more extreme than in the disk of the galaxy with molecular gas properties similar to those seen in galaxies at z~2. While the CMZ hosts several massive star clusters, the formation of stars from these dense molecular clouds and the feedback of these massive stars on the ISM is not well understood. I present in my thesis a case study of a few regions in the CMZ using VLA continuum and spectral line observations. I explore feedback eects of recent star formation (a young massive stellar cluster) on the surrounding ISM (molecular and ionized gas). Using the kinematic information of molecular and ionized gas, obtained dierent species of spectral lines, I will determine the line of sight geometry of the dierent gas components. I will then establish the relationship of these components to the larger structure of molecular gas in the CMZ.
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Svoboda, Brian E., Yancy L. Shirley, Cara Battersby, Erik W. Rosolowsky, Adam G. Ginsburg, Timothy P. Ellsworth-Bowers, Michele R. Pestalozzi, et al. "THE BOLOCAM GALACTIC PLANE SURVEY. XIV. PHYSICAL PROPERTIES OF MASSIVE STARLESS AND STAR-FORMING CLUMPS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621258.
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We sort 4683 molecular clouds between 10 degrees < l < 65 degrees from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 mu m sources, mid-IR color-selected YSOs, H2O and CH3OH masers, and UCH II. regions. We also present a combined NH3-derived gas kinetic temperature and H2O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial (alpha similar to 0.7) with >75% of clumps with known distance being gravitationally bound (alpha < 2). These samples show a statistically significant increase in the median clump mass of Delta M similar to 170-370 M-circle dot from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at (M) over dot similar to 200-440 M-circle dot Myr(-1) for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii). a variation in the ratio of starless to protostellar clump lifetime that scales as similar to M-0.4. By comparing to the observed number of CH3OH maser containing clumps, we estimate the phase. lifetime of massive (M > 10(3) M-circle dot) starless clumps to be 0.37 +/- 0.08 Myr (M/10(3) M-circle dot)(-1); the majority (M < 450 M-circle dot) have phase. lifetimes longer than their average freefall time.
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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.
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Draper, Aden R. "Understanding the connection between active galactic nuclei and host star formation through multi-wavelength population synthesis modeling." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45748.
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Supermassive black holes, black holes with masses <106 Msun, are found at the centers of all massive galaxies. These massive black holes grew from smaller seed black holes through accretion events. Accreting black holes are very bright in the radio through very hard X-ray spectral regimes. Due to the location of these accreting black holes at the centers of galaxies, they are referred to as active galactic nuclei (AGN). It is understood that AGN are an important phase of galaxy evolution; however, the role of AGN in massive galaxy formation is very poorly constrained. Here, the unique tool of multi-wavelength population synthesis modeling is used to study the average properties of AGN and their host galaxies with a focus on host galaxy star formation and the role of black hole growth in galaxy evolution. Knowledge of the AGN population from deep X-ray surveys is combined with theoretical AGN spectral energy distributions to predict various observables of the AGN population in wavelength regions from the far infrared to very hard X-rays. Comparison of the model predictions to observations constrains the model input parameters and allows for the determination of average properties of the AGN population. Particular attention is paid to a special class of AGN known as Compton thick AGN. These AGN are deeply embedded in gas and dust such that the column density obscuring the line of sight to the central engine of the AGN exceeds 1/σT ~ 10²⁴ cm⁻², where σT is the Thomson cross-section of the electron---a column density comparable to that of the human chest. Theoretical and simulational evidence suggest that these Compton thick AGN may be recently triggered, rapidly accreting AGN, making them of special interest to researchers. I found that Compton thick AGN are likely to contribute ~20% of the peak of the cosmic X-ray background (XRB) at ~30 keV and demonstrated that a significant portion of Compton thick AGN may be accreting very rapidly. Moreover, Compton thick AGN do not appear to follow the orientation based unified model of AGN. According to the unified model, AGN exhibit a range of obscuration levels due to a dusty 'torus' which, depending on the orientation of the torus to the observer's line of sight, may obscure the central engine of the AGN. Upon further investigation into the stellar populations of AGN host galaxies, it appears that the unified model holds in general at z < 1, but not at z > 1. I found that this is likely due to the dominant triggering mechanism of AGN switching from major mergers at z > 1.5 to secular processes by z ~ 1.
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Hayes, Christian R., Steven R. Majewski, Matthew Shetrone, Emma Fernández-Alvar, Carlos Allende Prieto, William J. Schuster, Leticia Carigi, et al. "Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/626539.
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We find two chemically distinct populations separated relatively cleanly in the [Fe/H]-[Mg/Fe] plane, but also distinguished in other chemical planes, among metal-poor stars (primarily with metallicities [Fe/H] < -0.9) observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and analyzed for Data Release 13 (DR13) of the Sloan Digital Sky Survey. These two stellar populations show the most significant differences in their [X/Fe] ratios for the alpha-elements, C+N, Al, and Ni. In addition to these populations having differing chemistry, the low metallicity high-Mg population (which we denote "the HMg population") exhibits a significant net Galactic rotation, whereas the low-Mg population (or "the LMg population") has halo-like kinematics with little to no net rotation. Based on its properties, the origin of the LMg population is likely an accreted population of stars. The HMg population shows chemistry (and to an extent kinematics) similar to the thick disk, and is likely associated with in situ formation. The distinction between the LMg and HMg populations mimics the differences between the populations of low-and high-a halo stars found in previous studies, suggesting that these are samples of the same two populations.
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Langer, Mathieu. "Origine du champ magnétique en cosmologie et formation des galaxies." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2002. http://tel.archives-ouvertes.fr/tel-00002495.
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Ma thèse est le fruit d'un travail théorique centré sur deux questions fondamentales de la cosmologie actuelle: la formation des galaxies d'une part, et l'origine des champs magnétiques à grande échelle d'autre part. Je propose une solution au problème du sur-refroidissement dont souffrent les modèles de formation des galaxies. Pour cela, à l'aide d'un modèle analytique simple, puis au moyen de simulations numériques, j'explore les mécanismes de transfert et de stockage d'énergie par ondes d'Alfvén en œuvre dans le milieu interstellaire (MIS) biphasique. Je montre d'une part que les interférences des ondes internes aux nuages du MIS, négligées dans les études précédentes, renforcent l'efficacité d'injection d'énergie. D'autre part, les mouvements des nuages redistribuent l'énergie à l'échelle du système entier. Ils injectent aussi de l'énergie dans les nuages. Les modes vibratoires internes excités s'opposent à la compression des nuages et prolongent la durée de vie du système. Les nuages magnétisés constituent alors un réservoir d'énergie sur plusieurs temps dynamiques. A l'aide d'un modèle de protogalaxie biphasique, je montre que la dynamique des nuages du MIS et celle d'une protogalaxie sont équivalentes. Pour résoudre le sur-refroidissement, je propose la transposition des résultats du MIS au cas protogalactique. Malgré les diverses tentatives passées, l'origine du champ magnétique en cosmologie n'a pas trouvé d'explication satisfaisante. Or, sa place au sein du MIS et son rôle dans la formation des galaxies sont manifestes. Je propose dans ma thèse un nouveau mécanisme de magnétogenèse efficace à grande échelle, opérant à la réionisation de l'Univers, et reposant sur la pression de radiation anisotrope et inhomogène fournie par les premières structures lumineuses. A l'échelle galactique, le champ magnétique que j'obtiens est huit ordres de grandeur plus intense que dans les modèles habituels. De plus, il est généré avant tout aux grandes échelles, les champs à petite échelle étant largement supprimés. Ces deux propriétés permettent au modèle proposé de rendre compte des champs observés dans les grandes structures.
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Lotz, Marcel [Verfasser], and Andreas [Akademischer Betreuer] Burkert. "Evolution of galactic star formation in galaxy clusters and post-starburst galaxies / Marcel Lotz ; Betreuer: Andreas Burkert." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2021. http://d-nb.info/1232176338/34.
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Feltre, Anna. "Multi-band Emission of Active Galactic Nuclei: the Relationship of Stellar and Gravitational-Accretion Activity." Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3423457.
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One of the remaining open issues in the context of the analysis of active galactic nuclei is the evidence that nuclear gravitational accretion is often accompanied by a concurrent starburst activity. What is, in this picture, the role played by the obscuring dust around the nucleus and what does the state of the art models have to say? Can the infrared data provided by Spitzer and Herschel help us in extensively investigate both phenomena and, if so, how and with what limitations? Does the presence of an active nucleus have an impact in the mid- and far-infrared properties of galaxies? Which are the effects of simultaneous nuclear gravitational accretion and starburst activities in these same galaxies?
This Thesis presents our contribution to the efforts of answering these questions. I report on results coming from a comparative study of various approaches adopted while modelling active galactic nuclei, focusing mostly on the much-debated issue about the morphology of the dust distribution in the toroidal structure surrounding their nuclear centre. We largely illustrate that properties of dust in active galactic nuclei as measured by matching observations (be it broad band infrared photometry or infrared spectra) with models strongly depend on the choice of the dust distribution.
Further, I describe a spectral energy distribution fitting tool appositely developed to derive simultaneously the physical properties of active nuclei and coexisting starbursts. The procedure was developed to make the best use of Spitzer and Herschel mid- and far-infrared observations. Such data play a crucial role in this context, providing much stronger constraints on the models with respect to the previous observing facilities. The tool has been applied to a large sample of extragalactic sources representing the Herschel/Multi-tiered Extragalactic Survey population with mid-infrared spectra from Spitzer and with a plethora of multi-wavelength data (SDSS, Spitzer and Herschel/SPIRE). The goal of such work is to study the impact of a possible presence of an active nucleus on the host galaxy's properties. Finally, I present the main results obtained. In particular, I focus on the analysis of the star formation rate in connection to the presence of an active nucleus and on the
comparison of the properties of the hot, heated by the active nucleus, and cold, starburst heated, dust components.Una delle questioni ancora aperte nell'ambito dell'analisi dei nuclei galattici attivi riguarda il fatto che l'accrescimento gravitazionale nucleare è spesso accompagnato da una concomitante attività di formazione stellare . Qual è, in questo contesto, il ruolo assunto dalla polvere oscurante che circonda il nucleo e cosa può dirci lo stato dell'arte dei modelli a riguardo? Riescono i dati infrarossi dei satelliti Spitzer e Herschel a permettere uno studio approfondito di entrambi i fenomeni e, in tal caso, come e con quali limitazioni? La presenza di un nucleo attivo ha effettivamente un impatto sulle proprietà medio e lontano infrarosse delle galassie ospiti? Quali sono gli effetti della simultaneità dell'accrescimento gravitazionale nella regione nucleare e dell'attività di formazione stellare in queste stesse galassie? In questa Tesi viene esposto il nostro contributo al tentativo di rispondere a queste domande. Vengono presentati i risultati di uno studio comparativo tra diversi approcci usati per modellare i nuclei galattici attivi, focalizzandosi soprattutto sulla questione, attualmente ancora molto dibattuta, relativa alla morfologia della distribuzione della polvere nella struttura toroidale che circonda il centro del nucleo. Viene mostrato in maniera esaustiva che le proprietà della polvere dei nuclei attivi, ottenute dal confronto tra modelli e osservazioni (sia fotometria infrarossa a banda larga che spettro medio infrarosso), dipendono fortemente dalle assunzioni sulla distribuzione della polvere. Viene fornita, inoltre, una descrizione dettagliata della tecnica di sintesi spettrofotometrica sviluppata allo scopo di ricavare contemporaneamente le proprietà fisiche dei nuclei attivi a delle coesistenti galassie ''starburst''. Tale procedura è stata sviluppata per sfruttare al meglio le osservazioni medio e lontano infrarosse dei satelliti Spitzer e Herschel. In questo contesto, tali dati giocano un ruolo cruciale fornendo vincoli molto più forti sui modelli rispetto alle precedenti strutture osservative. Il codice di sintesi spettrofotometrica è stato usato su un vasto campione di sorgenti extragalattiche rappresentanti la popolazione della Herschel/Multi-tiered Extragalactic Survey per le quali erano disponibili sia lo spettro medio infrarosso di Spitzer che un pletora di dati multi-banda (SDSS, Spitzer e Herschel/SPIRE). L'obiettivo di tale lavoro è quello di studiare l'impatto che l'eventuale presenza di un nucleo attivo potrebbe avere sulle proprietà delle galassie ospiti. Infine, vengono presentati i principali risultati ottenuti, con particolare attenzione all'analisi del tasso di formazione stellare in relazione alla presenza di un nucleo attivo e al confronto delle proprietà della polvere calda, riscaldata dal nucleo attivo stesso, e fredda, riscaldata dalla formazione stellare.
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Boissier, Samuel. "Formation Stellaire Aux Échelles Des Galaxies." Habilitation à diriger des recherches, Aix-Marseille Université, 2012. http://tel.archives-ouvertes.fr/tel-00761183.
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La formation des étoiles est au coeur du cycle d'évolution des galaxies. A partir de leur réservoir de gaz (et de son remplissage éventuel par accrétion ou fusion), des étoiles se forment à un taux appelé par définition le taux de formation Stellaire (soit SFR pour Star Formation Rate en anglais), avec un impact énorme sur de nombreux aspects de l'évolution des galaxies. Cette HDR présente tout d'abord le formalisme de la formation stellaire (SFR, IMF), quelques suggestions théoriques concernant les phénomènes affectant le SFR sur diverses échelles spatiales dans les galaxies, les méthodes de détermination empirique du SFR à partir d'observables. Une partie importante est dédiée aux "lois" de formation stellaire (e.g. loi de Schmidt) sur diverses échelles (loi locale, loi radiale, loi globale). Finalement, la dernière partie concerne les plus grandes échelles (évolution du SFR "cosmique" et effet d'environnement.
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Kordopatis, Georges. "Archéologie galactique : contraintes observationnelles aux modèles de formation du disque épais." Phd thesis, Observatoire de Paris, 2011. http://tel.archives-ouvertes.fr/tel-00736775.
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L'archéologie galactique consiste à retrouver les signatures fossiles des accrétions passées de la Voie Lactée, grâce à l'identification et la caractérisation des populations stellaires qui composent notre Galaxie. Le but de cette thèse est de mieux comprendre la formation du disque épais de notre Galaxie, en se basant sur ∼700 spectres stellaires de basse résolution, obtenus dans le proche infra-rouge. Les outils et méthodes développés au cours de ce travail serviront au traitement et à l'interprétation future des données de la mission Gaia, qui collectera des spectres dans une configuration semblable à celle de l'échantillon observé. Se basant sur les algorithmes de paramétrisation spectrale automatique MATISSE et DEGAS, une procédure de traitement des spectres combinant de façon optimale ces deux approches a été proposée, afin d'estimer les paramètres atmosphériques des étoiles (température effective, gravité de surface, métallicité globale). Nous avons également déterminé les distances et positions galactocentriques des cibles, grâce à des modèles d'évolution stellaires, et nous avons effectué une caractérisation cinématique complète de l'échantillon. Les cibles appartenant au disque mince, disque épais et halo ont été sélectionnées, afin de caractériser chacune de ces sous-structures. Il a été trouvé que celles-ci sont bien des populations distinctes, caractérisées par des distributions chimiques et cinématiques différentes. De plus, les résultats ont montré que les propriétés du disque épais loin du voisinage solaire ne différaient que très peu de celles mesurées localement. Sans pour autant exclure de façon définitive des gradients verticaux intrinsèques dans le disque épais, les tendances en vitesse de rotation orbitale et en métallicité qui ont été mesurées ont pu être expliquées comme une transition continue du rapport entre les différentes composantes galactiques. De plus, une corrélation entre la vitesse orbitale de rotation et la métallicité a été détectée. Ce gradient suggère qu'une migration radiale des étoiles à partir des rayons internes de la Galaxie ne peut pas être le processus dominant ayant formé le disque épais. Enfin, les estimations des échelles de hauteur et de longueur du disque épais en fonction de la métallicité, ainsi que la distribution en excentricité de ces étoiles, ne montrent pas de signatures de reliques d'un satellite massif accrété. Au vu de ces résultats, un scénario de formation du disque épais, basé sur plusieurs fusions mineures de galaxies satellites semble être privilégié. Enfin, les outils développés pour cette étude ont également été utilisés sur près de 2300 spectres observés vers le pôle sud galactique, ainsi que sur plus de 1200 cibles du satellite CoRoT. Les résultats qui en découlent ont permis d'imposer de nouvelles contraintes radiales et verticales sur les structures galactiques.
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Normandeau, Magdalen. "The Galactic plane survey pilot project, the interstellar medium environment of the w3/w4/w5 star formation complex." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq20761.pdf.
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Fukumura, Keigo. "Relativistic Accretion Flows onto Supermassive Black Holes: Shock Formation and Iron Fluorescent Emission Lines in Active Galactic Nuclei." Thesis, Montana State University, 2005. http://etd.lib.montana.edu/etd/2005/fukumura/FukumuraK0505.pdf.
Full textAbstract:
One of the exciting discoveries from the recent X-ray spectroscopic studies of active galactic nuclei (AGNs) is the so called "relativistically-broadened iron fluorescent emission line" often detected in the hard X-ray spectra. It is generally believed to originate from the inner part of the accretion disk surrounding a supermassive black hole (BH) at the center. Although we have begun to obtain some physical insight regarding such emission lines supported by theoretical models (e.g., disk-corona model), exactly how and where the observed fluorescence may take place is still disputable. Here, an X-ray data with XMM-Newton Observatory of a typical narrow-line Seyfert 1 galaxy, NGC 4051, is analyzed based on a partial covering model to consistently explain the observed time-resolved temporal/spectral variations. This model implies that the intrinsic emission varies significantly in the presence of the covering cloud. We often detect a hard X-ray continuum originating from a hot region close to the central engines of AGNs. As a promising X-ray source candidate, relativistic hydrodynamic (HD) shocks are investigated systematically and then extended to the magnetohydrodynamic (MHD) shocks, given the widely accepted suggestion that the presence of the magnetic fields could play an important role in the accreting flows. I show that both HD and MHD shocks can form in the vicinity of the BH, perhaps responsible for creating such a high temperature region where hard X-rays are produced. Particularly in the MHD shocked plasma, the hydro/magneto-dominated states are found. Considering the effect of such magnetic fields in the accretion disk, I calculate nonstandard iron fluorescent line profiles in the presence of spiral density waves and find multiple sharp sub-peak structures in extremely skewed line profiles, which will be detectable with upcoming X-ray satellites such as Astro-E2 XRS for testing the model. This dissertation is the result of my own work and also includes some work done in collaboration. Parts of this dissertation have been either already published in or submitted to the Astrophysical Journal and presented at conferences, while some are still in progress.
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Talia, Margherita <1983>. "The Universe 10 Billion years ago: Morphologies, Star-formation rates and Galactic-scale winds in z ∼ 2 Galaxies." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5206/1/TALIA_MARGHERITA_tesi.pdf.
Full textAbstract:
This thesis is devoted to the study of the properties of high-redsfhit galaxies in the epoch 1 < z < 3, when a substantial fraction of galaxy mass was assembled, and when the evolution of the star-formation rate density peaked. Following a multi-perspective approach and using the most recent and high-quality data available (spectra, photometry and imaging), the morphologies and the star-formation properties of high-redsfhit galaxies were investigated.
Through an accurate morphological analyses, the built up of the Hubble sequence was placed around z ~ 2.5. High-redshift galaxies appear, in general, much more irregular and asymmetric than local ones. Moreover, the occurrence of morphological k-correction is less pronounced than in the local Universe. Different star-formation rate indicators were also studied. The comparison of ultra-violet and optical based estimates, with the values derived from infra-red luminosity showed that the traditional way of addressing the dust obscuration is problematic, at high-redshifts, and new models of dust geometry and composition are required. Finally, by means of stacking techniques applied to rest-frame ultra-violet spectra of star-forming galaxies at z~2, the warm phase of galactic-scale outflows was studied. Evidence was found of escaping gas at velocities of ~ 100 km/s. Studying the correlation of inter-stellar absorption lines equivalent widths with galaxy physical properties, the intensity of the outflow-related spectral features was proven to depend strongly
on a combination of the velocity dispersion of the gas and its geometry.