Literatura científica selecionada sobre o tema "Galaxie : structure"
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Artigos de revistas sobre o assunto "Galaxie : structure"
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Fan, Yi-Liu. "Theoretical Analysis of Moving Galaxies in the Large Scale Structure of SpaceTime." Space Science Journal 1, no. 2 (2024): 01–08. http://dx.doi.org/10.33140/ssj.01.02.05.
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In this paper we will make further theoretical analysis for the validity of the accelerating universe based on General Relativity and three new problems of the standard model of the universe are presented from different perspectives. The first part, analyzed the explosion mechanism of the cosmic initial singularity and put forward a different view from the rest. It’s virtually impossible to start with a giant explosion, the big bang by now cosmologists had refined the idea. The second part devised a new model of the twin paradox. It’s one in which people have been consider to include both special and general relativity in the calculations to expose the counterintuitive weirdness of relativity theory. It seems to has a curious coincidence with the cat-a feline in a locked box that is both dead and alive until the box is opened-was a thought experiment devised by physicist Schr ö dinger. In part three the author makes determination on the cosmological deceleration parameter q0 by using mathematical derivation, and based on which to construct a thought experiment on cosmological redshift. It is needed to make a static model of the universe that both conforms to the Copernican principle and satisfies Hubble’s law and it’s possible to make us a fresh perspective and thought process.
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Masters, Karen L. "Galaxy Zoo 3D: Identifying Bars, Spirals and Foreground Stars in MaNGA Galaxy Data." Proceedings of the International Astronomical Union 17, S373 (2021): 39–41. http://dx.doi.org/10.1017/s1743921322004306.
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AbstractGalaxies, particularly disc galaxies, show a wide variety of internal structures (e.g. spirals, bars, and bulges). Mapping Nearby Galaxies at Apache Point Observatory (MaNGA, part of the fourth incarnation of the Sloan Digital Sky Surveys), obtained spatially resolved spectral maps for 10,010 nearby galaxies. Many results from MaNGA have collapsed this structure into azimuthally averaged radial gradients, or symmetric 2D shapes, but there is significantly more information about the effect internal structures have on the evolution of galaxies available if we can identify different internal structures. One of the simplest ways to identify irregular internal structures in galaxies is by visual inspection. By employing a citizen science technique to ask this question of N independent volunteers we have obtained quantitatively robust masks (and errors) for spirals and bars in MaNGA target galaxies. In addition to internal features the interface asked users to identify foreground stars and foreground/background galaxies.
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Ge, Xue, Yi-Zhou Gu, Cheng-Long Lei, and Xing-Han Zhang. "The connections among morphology, environment, and star formation with Galaxy Zoo Hubble." Monthly Notices of the Royal Astronomical Society 536, no. 1 (2024): 905–12. https://doi.org/10.1093/mnras/stae2569.
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ABSTRACT Morphology is an important implication for studying the formation and evolution of galaxies. Previous studies have investigated the effects of spiral arms on star formation activities, but it is not clear how clumpy structure affects this process. In this work, we combine Galaxy Zoo Hubble project and 3D-HST/Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey programs to study the influence of morphological structure on star formation processes and the relationship between morphology and the environment at $0 \lt z \lt 1.0$. We find that galaxies with spiral arms and clumpy structures have higher star formation rates than smooth galaxies, and as the redshift decreases, this result remains unchanged. Analysis based on the subsamples, We find that stellar mass is related to the number of arms but not to the number of clumps. In addition, we do not find that an increase in the numbers of arms and/or clumps stimulates greater star formation. We also find that less-clump galaxies preferentially inhabit high-density environments, while more-clump galaxies preferentially inhabit low-density environments. This phenomenon is not significant in spiral galaxies. Our results show that environmental effects may have a greater influence on clumpy structures compared to spiral arm structures, which in turn affects the star formation activities of galaxies.
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Shaver, PA. "Radio Surveys and Large Scale Structure." Australian Journal of Physics 44, no. 6 (1991): 759. http://dx.doi.org/10.1071/ph910759.
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An analysis of the Molonglo Reference Catalogue indicates that significant departures from isotropy are present in the sky distribution of strong extragalactic radio sources. This has been shown to be due to local large scale structure, specifically a concentration to the supergalactic plane, which also influences the slope of the source counts. A study of the three-dimensional distribution of local radio galaxies shows that they are more strongly concentrated to the supergalactic plane than are optically�selected galaxies, and that the supergalactic concentration is more extensive than hitherto believed. It appears that radio galaxies (and clusters of galaxies) trace the 'skeleton' of large scale structure, about which normal galaxies are more loosely distributed. Thus, while large scale structure evidently complicates the interpretation of radio source counts, it appears that radiO surveys can be of value in exploring structures on the largest scales.
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Nasution, Budiman, Ruben Cornelius Siagian, Winsyahputra Ritonga, Lulut Alfaris, Aldi Cahya Muhammad, and Arip Nurahman. "A Monte Carlo Density Distribution Model Study to Analyze Galaxy Structure, Mass Distribution, and Dark Matter Phenomena." Indonesian Review of Physics 6, no. 1 (2023): 24–44. http://dx.doi.org/10.12928/irip.v6i1.8240.
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This research uses the Monte Carlo density distribution model to study the structure and mass distribution of galaxies and the dark matter phenomenon. Through computer simulations, the research developed a mathematical model with parameters such as rho0, rc, beta, and others, to describe the structure and mass distribution of galaxies. The results show that the model can reproduce various galaxy structures, including groups, clusters and filaments, and influence the behavior and characteristics of individual galaxies. This research provides a deeper understanding of dark matter and its impact on the evolution of the universe. It has implications for improving our understanding of dark matter and the use of Monte Carlo density distribution models to study galaxies. This study provides new insights into the evolution of galaxies and their relationship with dark matter in cosmology. Using both physics and mathematical concepts, this research helps to understand the phenomenon of dark matter and the structure of galaxies, and provides a basis for further research on dark matter and galaxy evolution.
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Erwin, Peter. "The coexistence of classical bulges and disky pseudobulges in early-type disk galaxies." Proceedings of the International Astronomical Union 3, S245 (2007): 113–16. http://dx.doi.org/10.1017/s1743921308017419.
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AbstractClose examination of “pseudobulges” in several early-type disk galaxies indicates that they are actually composite structures consisting of both a flattened, kinematically cool disklike structure (“disky pseudobulge”) and a rounder, kinematically hot spheroidal structure (“classical bulge”). This indicates that pseudobulges, thought to form from internal secular evolution, and classical bulges, thought to form from rapid mergers, are not exclusive phenomena: some galaxies can have both.
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Yee, H. K. C., M. J. Sawicki, R. G. Carlberg, et al. "The CNOC2 Field Galaxy Redshipt Survey." Highlights of Astronomy 11, no. 1 (1998): 460–63. http://dx.doi.org/10.1017/s153929960002178x.
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Fundamental to our understanding of the universe is the evolution of structures, from galaxies to clusters of galaxies to large-scale sheets and filaments of galaxies and voids. The investigation of the evolution of large-scale structure not only provides us with the key test of theories of structure formation, but also allows us to measure fundamental cosmological parameters. The CNOC2 (Canadian Network for Observational Cosmology) Field Galaxy Redshift Survey is the first large redshift survey of faint galaxies carried out with the explicit goal of investigating the evolution of large scale structure. This survey also provides the largest redshift and photometric data set currently available for the study of galaxy population and evolution at the moderate redshift range between 0.1 and 0.6. In this paper we describe the scope and technique of the survey, its status, and some preliminary results.
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Gao, Tiao. "State-of-art Simulations and Observations for Star Formation." Highlights in Science, Engineering and Technology 72 (December 15, 2023): 66–70. http://dx.doi.org/10.54097/fmnb7351.
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In recent year, the formation and formation of galaxies is a hot spot in astrophysics which has been widely investigated and discussed. On the basis of the theory of formation and formation of large-scale structures in modern cosmology, this study intends to systematically investigate and analyze the physical characteristics of galaxies in different stages, such as morphological structure, star family structure, gas accretion, stellar formation, black hole growth, chemical elements, stellar and gas movements, and their physical relationships with large-scale structures. According to the analysis and evaluations, it aims to reveal the physical origin and formation of galaxies in different stages, as well as their physical relationships with large-scale structures, and then summarize the universal physical laws affecting galaxy formation. Moreover, the current limitations of the state-of-art results will be demonstrated and prospects will be given accordingly. Overall, these results shed light on guiding further exploration of investigation of star formation.
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Fraser-McKelvie, A., L. Cortese, J. van de Sande, et al. "A SAMI and MaNGA view on the stellar kinematics of galaxies on the star-forming main sequence." Monthly Notices of the Royal Astronomical Society 503, no. 4 (2021): 4992–5005. http://dx.doi.org/10.1093/mnras/stab573.
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ABSTRACT Galaxy internal structure growth has long been accused of inhibiting star formation in disc galaxies. We investigate the potential physical connection between the growth of dispersion-supported stellar structures (e.g. classical bulges) and the position of galaxies on the star-forming main sequence at z ∼ 0. Combining the might of the SAMI and MaNGA galaxy surveys, we measure the λRe spin parameter for 3289 galaxies over $9.5 \lt \log M_{\star } [\rm {M}_{\odot }] \lt 12$. At all stellar masses, galaxies at the locus of the main sequence possess λRe values indicative of intrinsically flattened discs. However, above $\log M_{\star }[\rm {M}_{\odot }]\sim 10.5$ where the main sequence starts bending, we find tantalizing evidence for an increase in the number of galaxies with dispersion-supported structures, perhaps suggesting a connection between bulges and the bending of the main sequence. Moving above the main sequence, we see no evidence of any change in the typical spin parameter in galaxies once gravitationally interacting systems are excluded from the sample. Similarly, up to 1 dex below the main sequence, λRe remains roughly constant and only at very high stellar masses ($\log M_{\star }[\rm {M}_{\odot }]\gt 11$), do we see a rapid decrease in λRe once galaxies decline in star formation activity. If this trend is confirmed, it would be indicative of different quenching mechanisms acting on high- and low-mass galaxies. The results suggest that whilst a population of galaxies possessing some dispersion-supported structure is already present on the star-forming main sequence, further growth would be required after the galaxy has quenched to match the kinematic properties observed in passive galaxies at z ∼ 0.
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HAQUE-COPILAH, S., and A. ACHONG. "THE FILAMENTARY NATURE OF PISCES-PERSEUS." International Journal of Modern Physics D 12, no. 03 (2003): 527–39. http://dx.doi.org/10.1142/s0218271803003141.
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Minimal Spanning Tree (MST) statistics and associated reducing procedures have been used to establish the level of filamentary structure, if any in Pisces-Perseus, a sample containing 4501 galaxies. The procedure has been applied to subsets of galaxies with 247 galaxies that we call the Most Conspicuous sample which contain the larger intrinsic linear diameters and the brighter galaxies, and to the Least Conspicuous samples with 253 galaxies containing the smaller intrinsic linear diameter and the fainter members as well as the entire sample. The results show that there are longer filaments in the Most Conspicuous samples with less coiling as opposed to the Least Conspicuous sample. Pruning and separating also highlight the key structures in this region and not only the filamentary ones. Voids are highlighted, also indicating that MST's can be used to identify voids in the large scale structure of the Universe.
Teses / dissertações sobre o assunto "Galaxie : structure"
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Nieuwmunster, Niels. "Les systèmes les plus denses de l'Univers : le disque nucléaire." Electronic Thesis or Diss., Université Côte d'Azur, 2024. http://www.theses.fr/2024COAZ5041.
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Comprendre la formation et l'évolution des galaxies, et en particulier de leurs centres galactiques, est l'une des questions les plus intrigantes de l'astrophysique moderne. De nombreuses galaxies spirales comme la Voie lactée présentent en leur centre un disque nucléaire (NSD). Celui de la Voie lactée est, avec l'amas central et le trou noir super massif central, l'une des principales composantes internes et l'un des meilleurs laboratoires locaux disponibles pour étudier l'évolution des galaxies. En raison de la forte extinction, de l'importante densité d'étoiles et de la superposition de multiples structures le long de la ligne de visée, les études des régions internes de la Voie Lactée sont cependant très difficiles et très peu ont été réalisées jusqu'à présent. Grâce à des données récentes, cette thèse vise à dévoiler les processus physiques qui ont conduit à la formation du NSD et ses liens avec les autres composantes de la Voie Lactée. Ce manuscrit est divisé en trois parties correspondant aux différentes méthodologies utilisées. Pour la première partie, grâce à la spectroscopie en proche infrarouge à haute résolution, j'ai effectué une analyse chimique d'étoiles géantes froides situées dans le bulbe Galactique interne. J'ai mesuré les abondances détaillées des éléments alpha : silicium, magnésium et calcium, en utilisant des données théoriques récentes et précises telles qu'une liste de raies mise à jour, des paramètres d'élargissement et les corrections de l'équilibre thermodynamique non local. Sur la base des abondances dérivées, un modèle d'évolution chimique adapté au bulbe Galactique interne a été construit. J'ai également utilisé l'analyse spectrale pour mesurer automatiquement le rapport isotopique du carbone dans les étoiles géantes du voisinage solaire afin d'établir une relation avec la masse stellaire astérosismique. Cela permettrait d'estimer les âges stellaires dans des régions éloignées telles que le NSD. Dans la deuxième partie de cette thèse, j'ai étudié la dynamique des étoiles observées dans le NSD de la Voie Lactée en faisant une analyse orbitale. J'ai calculé les orbites dans un potentiel gravitationnel non-axisymétrique tenant compte des effets de la barre Galactique et j'ai dérivé leurs fréquences fondamentales. Cela m'a permis d'identifier les résonances orbitales et les différentes familles d'orbites qui peuvent être présentes dans le NSD. En plus des observations, les simulations sont d'un grand intérêt pour comprendre les processus physiques qui ont formé les régions internes de la Galaxie. Dans cette dernière partie, j'ai utilisé une simulation hydrodynamique à N-corps d'une galaxie isolée semblable à la Voie Lactée afin d'étudier la formation de son NSD. Cette simulation a permis de faire une première comparaison entre les observations et les simulations en termes de chimie et de dynamique<br>Understanding the formation and evolution of galaxies and in particular their galactic centres is one of the most intriguing questions in modern astrophysics. Many spiral galaxies like the Milky Way feature a nuclear stellar disc (NSD) in their centre. The Milky Way's NSD is, together with the nuclear star cluster and the central super massive black hole, one of the main inner components and best local laboratories available for studying galaxy evolution. Because of high extinction, crowding, and the superposition of multiple structures along the line of sight, studies of the inner regions of the Milky Way are however very challenging and very little has been done so far. Thanks to recent data, this thesis aims at unveiling the physical processes which led to the formation of the NSD and its links with the other components of the Milky Way. This manuscript is divided into three parts corresponding to the different methodologies used.For the first part, thanks to high-resolution near-infrared spectroscopy, I carried out a chemical analysis of cool giant stars located in the inner Galactic bulge. I measured detailed abundances of the alpha-elements: silicon, magnesium and calcium, using recent and precise theoretical data such as an updated line list, broadening parameters and non-local thermodynamic equilibrium corrections. Based on the derived abundances, a tailored chemical evolution model for the inner Galactic bulge was constructed. I also used spectral analysis to measure the carbon isotopic ratio automatically in solar neighbourhood giant stars in order to establish a relation with asteroseismic stellar mass. This would allow to estimate stellar ages in distant regions such as the NSD.In the second part of this thesis, I studied the dynamics of stars observed in the Milky Way's NSD by doing an orbital analysis. I computed orbits in a non-axisymmetric gravitational potential accounting for the effects of the Galactic bar and derived their fundamental frequencies. This allowed me to identify the orbital resonances and then the different orbit families that may be present in the NSD.In addition to observations, simulations are of great interest to fully understand the physical processes that formed the inner regions of the Galaxy. In this final part, I used a N-body hydrodynamic simulation of an isolated Milky Way like galaxy in order to study the formation of its NSD. This simulation allowed to do a first comparison between observations and simulations in terms of chemistry and dynamics
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Machado, murtinheiras martins Andre. "Statistical analysis of large scale surveys for constraining the Galaxy evolution." Thesis, Besançon, 2014. http://www.theses.fr/2014BESA2026/document.
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La formation et l'évolution du disque épais de la Voie Lactée restent controversées. Nous avons utilisé un modèle de synthèse de la population de la Galaxie, le Modèle de la Galaxie de Besançon (Robin et al., 2003), qui peut être utilisé pour l'interprétation des données, étudier la structure galactique et tester différents scénarios de formation et évolution Galactique. Nous avons examiné ces questions en étudiant la forme et la distribution de métallicité du disque mince et du disque épais en utilisant l'approche de synthèse de la population. Nous avons imposé sur des simulations les erreurs d'observation et les biais afin de les rendre directement comparables aux observations. Nous avons corrigé les magnitudes et les couleurs des étoiles de la simulation, en utilisant un modèle d'extinction. Les modèles d'extinction disponibles ne reproduisent pas toujours la quantité exacte d'extinction le long de la ligne de visée. Un programme a été développé pour corriger la distribution de l'extinction en fonction de la distance le long de ces lignes. Les extinctions correctes ont ensuite été appliquées sur les simulations du modèle. Nous avons étudié la forme du disque mince en utilisant des données photométriques aux basses latitudes du sondage SDSS-SEGUE. Nous avons comparé qualitativement et quantitativement les observations et les simulations et nous avons essayé de contraindre la fonction de masse initiale. En utilisant la spectroscopie du relevé SEGUE, nous avons sélectionné les étoiles du turn-off de la séquence principale (MSTO) (Cheng et al 2012) et des géantes K pour étudier la distribution de métallicité du disque mince et du disque épais. Nous avons calculé une estimation de distance pour chaque étoile à partir de la relation entre les températures effectives et magnitudes absolues pour les catalogues observés et simulés. Ces deux catalogues ont les mêmes biais sur les distances, elles sont donc comparables. Nous avons développé un outil basé sur une méthode MCMC-ABC pour déterminer la distribution de la métallicité et étudier les corrélations entre les paramètres ajustés. Nous avons confirmé la présence d'un gradient de métallicité radiale de -0.079 ± 0.015 dex kpc−1 pour le disque mince. Nous avons obtenu une métallicité du disque épais au voisinage solaire de -0.47 ± 0.03 dex, compatible avec les résultats obtenus par les études précédentes. De plus, le disque épais ne montre pas de gradient, mais les données sont compatibles avec un gradient positif intérieur suivi d'un négatif extérieur. Nous avons ensuite appliqué les outils développés au relevé spectroscopique Gaia-ESO et calculé la distribution de métallicité des étoiles F/G/K dans le disque mince et épais en supposant une formation en deux époques du disque épais de la Voie Lactée. Nous avons obtenu une métallicité locale dans le disque épais de -0.23 ± 0.04 dex légèrement plus élevée que celle obtenue avec SEGUE mais en accord avec Adibekyan et al. (2013) et un gradient de métallicité radiale du disque épais en accord avec notre analyse précédente des données de SEGUE et la littérature. La métallicité locale est en accord avec la littérature au niveau de 3σ mais parce que les données GES sont préliminaires, une analyse plus approfondie avec plus de données et de meilleurs calibrations doit être faite. L'existence d'un gradient plat dans le disque épais peut être une conséquence d'une formation à partir d’un gaz turbulent et bien homogène, ou bien un fort mélange radial a brassé après coup les étoiles<br>The formation and evolution of the thick disc of the Milky Way remain controversial. We made use of a population synthesis model of the Galaxy, the Besançon Galaxy Model (Robin et al. 2003), which can be used for data interpretation, study the Galactic structure and test different scenarios of Galaxy formation and evolution. We examined these questions by studying the shape and the metallicity distribution of the thin and thick disc using the population synthesis approach. We imposed on simulations observational errors and biases to make them directly comparable to observations. We corrected magnitudes and colors of stars, from the simulation, using an extinction model. The available extinction models do not always reproduce the exact quantity of extinction along the line of sight. A code to correct the distribution of extinction in distance along these lines have been developed and the corrected extinctions have been applied on model simulations. We studied the shape of the thin disc using photometric data at low latitudes from the SDSS-SEGUE survey. We compared qualitatively and quantitatively observations and simulations and try to constrain the Initial Mass Function. Using the spectroscopic survey SEGUE we selected Main Sequence Turnoff (MSTO) stars (Cheng et al 2012) and K giants to study the metallicity distribution of the thin and thick discs. We computed a distance for each star from the relation between effective temperatures and absolute magnitudes for the observed and simulated catalogs. These two catalogues have the same biases in distances, therefore are comparable. We developed a tool based on a MCMC-ABC method to determine the metallicity distribution and study the correlations between the fitted parameters. We confirmed a radial metallicity gradient of -0.079 ± 0.015 dex kpc−1 for the thin disc. We obtained a solar neighborhood metallicity of the thick disc of -0.47 ± 0.03 dex similar to previous studies and the thick disc shows no gradient but the data are compatible with an inner positive gradient followed by a outer negative one. Furthermore, we have applied the developed tools to the Gaia-ESO spectroscopic survey and computed the metallicity distribution of F/G/K stars in the thin and thick disc assuming a two epoch formation for the thick disc of the Milky Way. We obtained a local metallicity in the thick disc of -0.23 ± 0.04 dex slightly higher than the one obtained with SEGUE but in agreement with Adibekyan et al. (2013) and a radial metallicity gradient for the thick disc in agreement with our previous analysis of SEGUE data and the literature. The local metallicity is in fair agreement with literature at the 3σ level but because the GES data is an internal release under testing further analysis with more data and better calibrations have to be done. The existence of a flat gradient in the thick disc can be a consequence of an early formation from a highly turbulent homogeneous well mixed gas, unless it has suffered heavy radial mixing later on
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Siebert, Arnaud. "Structure et dynamique des disques de la Galaxie." Université Louis Pasteur (Strasbourg) (1971-2008), 2003. http://www.theses.fr/2003STR13036.
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Jesseit, Roland. "The orbital structure of galaxies and dark matter halos in N-body simulations." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=970059388.
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Pohlen, Michael. "The radial structure of galactic stellar disks surface photometric study on disk galaxies /." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=964128535.
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Conn, Anthony Rhys. "Structure of the M31 satellite system : bayesian distances from the tip of the red giant branch." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-01012081.
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This study focuses on the spatial distribution of the M31 satellite system. A new Bayesian technique for determining object distances from the Tip of their Red Giant Branch is developed and used to obtain distance probability distributions for M31and 27 of its satellite galaxies. These distances are then used to calculate the satellite positions in three dimensions. Subsequent analysis of the resulting spatial distribution reveals striking inhomogeneity, with roughly half of the satellites confined to a curiously oriented thin disk. The distribution is also markedly asymmetric, with the majority of satellites lying on the Milky Way side of M31.
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Martin, Nicolas. "A la recherche de structures stellaires du disque galactique au halo de la galaxie d'Andromède." Université Louis Pasteur (Strasbourg) (1971-2008), 2006. https://publication-theses.unistra.fr/public/theses_doctorat/2006/MARTIN_Nicolas_2006.pdf.
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Cette thèse a pour but la recherche et l’étude des structures stellaires résultant de l’accrétion de galaxies naines par notre Voie Lactée ou la galaxie d’Andromède (M31). En effet, les théories actuelles sur la formation des halos de galaxies indiquent qu’ils pourraient se construire avec le temps par l’absorption successive de petites structures galactiques. Dans la théorie LCDM actuellement privilégiée, plusieurs centaines de ces fragments proto-galactiques sont nécessaires pour former le halo d’une grosse galaxie comme la Voie Lactée ou M31. Les importantes forces de marée misent en jeu détruisent ces structures et produisent des courants d’étoiles et de matière noire le long de leur orbite. Bien que l’étude de ces structures est nécessaire pour comprendre la formation des galaxies, seuls les courants les plus massifs ont jusqu’à présent été étudiés : celui qui est produit par l’accrétion de la galaxie naine du Sagittaire autour de notre Galaxie et un courant géant qui s’étend sur plus de 100 kiloparsecs dans le halo de la galaxie d’Andromède. Afin de comprendre la formation du Groupe Local et la répartition de la matière noire dans les halos, il est primordial de détecter et de quantifier les courants d’accrétions plus anciens ou provenant de plus petits satellites. La publication de catalogues d’étoiles couvrant une part importante du ciel (2MASS, DENIS, SDSS) est une étape importante dans cette recherche car ils permettent de sonder et d’étudier en détail le halo et les régions extérieures du disque Galactique. En particulier, notre connaissance des parties extérieures des disques galactiques a été grandement modifiée par la découverte de nombreuses structures stellaires qui semblent être les restes de galaxies naines accrétées sur la Voie Lactée. Des structures similaires ont aussi été mises en évidence autour de la galaxie d’Andromède et pourraient indiquer un comportement général des galaxies spirales. Sur les bords de la Voie Lactée, la plus évidente de ces structures est l’Anneau de la Licorne, une structure stellaire qui semblent entourer le disque Galactique. La première partie de cette thèse se concentre sur la recherche du progéniteur de cet Anneau. A partir du catalogue stellaire 2MASS qui couvre tout le ciel dans l’infra-rouge proche, j’ai tracé la distribution des étoiles de la branche des géantes et des étoiles du Red Clump et ai révélé la présence d’une importante surdensité d’étoiles dans la constellation de Canis Major. Cette surdensité, restée jusqu’à présent cachée dans la poussière et la forte densité d’étoiles du disque Galactique, se situe au bord du disque, à environ un kiloparsec sous le plan Galactique. De forme elliptique, elle a une faible épaisseur et contient majoritairement une population stellaire d’ âge intermédiaire à ancien. Afin d’obtenir une meilleure compréhension de cette structure, je présente des données spectroscopiques de ses étoiles, obtenues à partir de trois instruments différents : un échantillon de près de 2 000 spectres observés avec le 2-degree Field sur l’Anglo-Australian Telescope dont la réduction a nécessité que je mette en place un nouveau protocole de réduction ; près de 1 000 spectres haute résolution observés avec l’instrument FLAMES monté sur le Very Large Telescope ; et plus de 600 spectres observés avec le nouvel instrument AAOMEGA, remplaçant du 2-degree Field. Ce dernier jeu de données représente les premières observations scientifiques obtenues avec cet instrument et, par comparaison avec les données FLAMES, je montre son très bon comportement. La comparaison de l’ensemble de ces données avec des modèles de la Voie Lactée montre que la surdensité de Canis Major ne peut être expliquée par notre connaissance actuelle de la morphologie de la Galaxie. J’en conclus que cette structure pourrait être les restes d’une accrétion dans le plan Galactique, potentiellement à l’origine de l’Anneau de la Licorne. Les étoiles de la surdensité suivent une orbite qui pourrait être compatible avec une telle accrétion et, par l’intermédiaire de simulations numériques, je montre en outre qu’un tel phénomène reproduit naturellement l’Anneau de la Licorne. Les vitesses radiales observées ne sont cependant pas incompatibles avec celles du disque Galactique et la structure pourrait aussi être une sous-structure du disque. L’analyse de plusieurs jeux de données me permet par ailleurs de révéler la présence de l’Anneau de la Licorne derrière la surdensité de Canis Major, devant la galaxie naine de Carina et devant la galaxie d’Andromède. L’ensemble de ces nouvelles détections permet de contraindre l’orbite du progéniteur de l’Anneau sur presque tout les deuxième et troisième quadrants Galactiques. Mes simulations indiquent que l’Anneau n’est pas une structure homogène mais doit être produit par la superposition sur le ciel des courants de marée d’une même accrétion, enroulés plusieurs fois autour de la Voie Lactée. Dans la deuxième partie de cette thèse, j’étudie le halo de la galaxie d’Andromède afin d’y quantifier les structures stellaires. En effet, une des difficultés majeures que rencontrent les modèles de formation galactique est leur surproduction, d’un facteur dix à cent par rapport aux observations, de satellites autour des galaxies telles la Voie Lactée ou la galaxie d’Andromède. Il est donc primordial de s’assurer que ces satellites, invisibles dans les observations effectuées jusqu’alors ne sont pas en fait fortement dominés par la matière noire et, de ce fait, très peu lumineux. Pour cette étude, j’utilise des données de la caméra grand champ Mega- Cam, montée sur le Télescope Canada-France-Hawaï. Le catalogue obtenu couvre un quart du halo de M31, d’une distance projetée de 50 à 150 kiloparsecs de celle-ci et il permet de suivre trois magnitudes de la branche des géantes de populations stellaires à cette distance. A partir de cet impressionnant relevé, je montre l’existence de seulement trois galaxies naines faiblement lumineuses dans cette partie du halo de la galaxie d’Andromède. La proximité de ces trois satellites et leur grande similitude pourraient par ailleurs indiquer qu’ils ont été amenés dans le halo de M31 par le même mécanisme. Une recherche automatique de sous-structures plus diffuses indique la présence d’une quinzaine de satellites potentiels qui pourraient donc résoudre le problème des satellites manquants s’ils sont confirmés par des observations plus profondes. Enfin, je montre que le halo extérieur de M31 présente aussi des signes d’accrétions passées. Le relevé me permet de mieux caractériser le courant de marée géant déjà mis en évidence. Je montre qu’il contient une population stellaire riche en métaux concentrée dans ses parties centrales, typique de l’accrétion d’une petite galaxie disque. Je mets par ailleurs en évidence plusieurs structures stellaires visibles jusqu’aux parties extérieures du halo de M31 et qui semblent être des courants d’accrétion diffus. L’ensemble de ces travaux montre que les halos de la Voie Lactée et de la galaxie d’Andromède sont, encore à notre époque, profondément influencés par les accrétions de galaxies satellites qui les peuplent de courants stellaires. L’étude de ces courants stellaires est donc primordiale pour comprendre l’histoire de la formation des galaxies.
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GOZ, DAVID. "Numerical simulations of galaxies in cosmological volumes." Doctoral thesis, Università degli Studi di Trieste, 2016. http://hdl.handle.net/11368/2908076.
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Modelling galaxy formation in a cosmological context is challenging due to many physical processes and a wide range of scales involved. It is then convenient to address the problem by means of numerical techniques. Cosmological simulations are still orders of magnitude away from capturing directly the spatial scales where stars actually form. The treatment of the interstellar medium, with multiple gas phases co-existing at very different densities and temperatures, needs to be included in simulations in the form of sub-resolution effective models.
In Murante et al. (2015), cosmological simulations of individual disk galaxies, carried out with GADGET-3 (Springel, 2005), are presented including the sub-resolution model MUlti-Phase Particle Integrator (MUPPI). Late-type galaxies are obtained with properties in broad agreement with observations (disk size, mass, surface density, rotation velocity, gas fraction) and also with results shown by other groups. During my PhD project, the properties of the bars in simulated galaxies are quantified and presented in Goz et al. (2015). Morphology, kinematic and radial streaming motions are in agreement with observations of local Universe (Seidel et al., 2015). In the GA galaxy, Fourier analysis of the surface density of the disk reveals that bar length and strength are remarkably independent of resolution. In the GA simulations, the onset of bar instability is found to take place when the disk is Toomre-unstable due to accumulation of mass in the disk. The complex task to calculate the emerging spectral energy distribution of a simulated galaxy, treating the reprocessing of light emitted by stars by means of dusty ISM, has been faced using the post-processing code GRASIL-3D (Dominguez-Tenreiro et al., 2014). During my PhD, GRASIL-3D has been interfaced with the outputs of the simulation and modified to better manage the quantities provided by the MUPPI algorithm. In this Thesis, results of a sample of simulated galaxies at z = 0 are shown, extracted from one large volume simulation presented by Barai et al. (2015), in which feedback and star formation are modelled by MUPPI. In broad agreement with observations of the local Universe, simulated galaxies reproduce the gas mass scaling, the main sequence, the relation between the gas-phase metallicity and stellar mass. Infrared predicted spectra, binned by stellar mass, gas metallicity, SFR and morphology, are remarkably in agreement with the available Herschel Reference Survey (Ciesla et al., 2014) templates calibrated with observations on nearby galaxies. H2 and HD are effective in cooling primordial gas below the temperature of ∼10^4 K, but usually the non-equilibrium radiative rates are only approximate in simulations, typically either assuming collisional ionization equilibrium or ignoring metal-line cooling altogether, rather than computing them explicitly. Maio et al. (2007) have extended a previous non-equilibrium calculations of Yoshida et al. (2003) in order to include in the numerical code GADGET a detailed chemical network and to follow the formation/destruction of a wide range of species, both with primordial and metal-enriched gas.
During my PhD project, the chemical network, presented by Maio et al. (2007), has been extended to take into account the H2 formation onto dust grains and its UV-photodissociation. Then, the modified chemical network has been coupled in two different preliminary forms with the MUPPI algorithm within GADGET-3. The main aim, motivated by the tight observed connection between molecular hydrogen and star formation (e.g. Kennicutt et al., 2007; Bigiel et al., 2008), is to devise a way to track self-consistently non-equilibrium abundance and cooling processes of H2 and H2-based star formation in smoothed particle hydrodynamic simulations.
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Beuret, Maxime. "Formation stellaire dans la galaxie et interaction avec le milieu interstellaire." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE017/document.
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Comment les étoiles se forment elles ?. Cette vaste question fait appel à des connaissances dans plusieurs domaines dont deux majeurs, la Formation Stellaire et le Milieu Interstellaire. C’est dans ce cadre générale que s’inscrit ma thèse. Notre galaxie est un vaste laboratoire d’études de cette formation et je me suis donc intéressé aux premières étapes de la formation des étoiles, allant du nuage moléculaire à la proto-étoile. J’ai principalement utilisé des données provenant du télescope Herschel qui nous fournit des images et des données dans l’infrarouge lointain et le domaine sub-milimétrique à une résolution inégalée. J’ai d’abord construit un catalogue de sources à l’aide d’un algorithme d’identification croisée, SPECFIND, puis appliqué un algorithme de clustering, MST, sur près de 100 000 sources afin de construire le premier catalogue d’amas d’objets stellaires jeunes à l’échelle galactique. Ceci m’a conduit à étudier les propriétés de ces amas et des sources les constituant<br>How stars form? This broad question uses knowledges in several areas, including two majors, the Star Formation and the Interstellar Medium. My thesis is a part of this overall framework. Our galaxy is a laboratory complex for the study of this formation. I became interested in the first stages of the star formations, from Molecular Clouds to protostars. I mainly used data from the Herschel telescope which provides us with images and data in the far infrared and sub-millimiter at an unparalleled resolution. First of all, I built a catalogue of young clumps using SPECFIND, an algorithm of cross-identification. Then I applied an algorithm of clustering, MST, over 100 000 young clumps to find over-densities in order to release the first catalogue of young stellar clusters in a galactic scale. Finally, I studied the physical properties of these clusters and their young clumps
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Terral, Philippe. "Structure du champ magnétique interstellaire dans le disque et le halo de notre galaxie." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30234/document.
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La caractérisation du champ magnétique interstellaire de notre Galaxie représente un enjeu majeur de l'astrophysique. Une meilleure connaissance de ses propriétés, en particulier de sa structure, constituerait en effet un atout important pour de nombreux domaines de recherche allant de l'étude des rayons cosmiques à la dynamique de la Galaxie en passant par l'évolution du milieu interstellaire et la formation stellaire. Des observations radio récentes ont permis de mettre en évidence des caractéristiques communes dans la structure magnétique de galaxies proches semblables à la Voie Lactée. Lorsque les galaxies sont vues de face, les lignes de champ magnétique forment un motif en spirale proche de celui observé dans le visible. Lorsque les galaxies sont vues par la tranche, les lignes de champ magnétique sont parallèles au plan galactique dans le disque et ont une forme dite en "X" dans le halo. Il est dès lors naturel de se poser la question de la présence d'une telle structure en X dans le halo de notre propre Galaxie. L'objectif du travail que j'ai effectué lors de mes trois années de thèse a consisté à tenter d'apporter des éléments de réponse à cette question. Les difficultés sont principalement de deux ordres : d'une part, notre position, à l'intérieur de la Voie Lactée ne nous permet pas d'avoir une vision globale de sa structure magnétique à grande échelle ; d'autre part, le champ magnétique est inaccessible à une observation directe, il est donc nécessaire de mettre en oeuvre des techniques indirectes estimant certaines des caractéristiques du champ magnétique à partir de l'effet qu'il peut avoir sur une observable donnée. Pour ma part, j'ai basé mon travail sur l'effet de rotation Faraday. J'ai tout d'abord constitué une carte de référence observationnelle de la profondeur Faraday de notre Galaxie associée au champ magnétique à grande échelle. Pour cela, j'ai dû développer un modèle simple de champ magnétique turbulent afin de pouvoir en soustraire sa contribution à la profondeur Faraday de celle du champ magnétique total. J'ai ensuite construit des cartes théoriques de la profondeur Faraday de notre Galaxie basées sur un ensemble de modèles analytiques du champ magnétique à grande échelle compatibles avec différentes contraintes (théoriques et observationnelles) et dépendant d'un nombre raisonnable de paramètres libres. J'ai finalement ajusté les valeurs de ces paramètres au travers d'une laborieuse phase d'optimisation. Mon manuscrit se décompose en quatre chapitres principaux. Au chapitre 1, je présenterai le contexte de mon travail et j'énoncerai divers résultats généraux utiles à mon étude. Au chapitre 2, je passerai en revue l'ensemble des éléments nécessaires à ma modélisation et j'insisterai particulièrement sur le jeu de modèles analytiques de champ magnétique que j'ai utilisés. Au chapitre 3, je décrirai les procédures de simulation et d'optimisation. Au chapitre 4, je présenterai mes résultats. Dans ce dernier chapitre, je dériverai les valeurs des paramètres des différents modèles de champ conduisant au meilleur accord avec les observations, je tâcherai de préciser le rôle de chaque paramètre et son impact sur la carte théorique, et je discuterai les géométries autorisées dans les différents cas. Je montrerai que l'accord modèle-observation est légèrement meilleur avec un champ du halo bisymétrique qu'avec un champ du halo axiisymétrique et que dans le premier cas, un motif en X apparaît naturellement dans les cartes de polarisation alors que le champ magnétique est horizontal dans le second cas<br>Characterization of the interstellar magnetic field of our Galaxy is a major challenge for astrophysics. A better understanding of its properties, particularly its structure, would be valuable in many research areas, from cosmic-ray studies to Galactic dynamics and including interstellar medium evolution and star formation. Recent radio observations uncovered common characteristics in the magnetic structure of nearby galaxies similar to the MilkyWay. In face-on galaxies, magnetic field lines appear to form a spiral pattern similar to that observed in the optical. In edge-on galaxies, magnetic field lines appear to be parallel to the galactic plane in the disc and X-shaped in the halo. One may naturally wonder whether such an X-shape structure is also present in the halo of our own Galaxy. The purpose of the work performed during my three years as a Ph.D. student was to try and provide some answers to this question. There are two major difficulties : on one hand, our location within the Milky Way does not mate it to have a global view of its large-scale magnetic structure; on the other hand, the magnetic field is not directly observable, so it is necessary to implement indirect techniques, based on the effect the magnetic field can have on a given observable, to estimate some characteristics of the magnetic field. My own work is based on Faraday rotation. I first built an observational reference map of the Faraday depth of our Galaxy associated with the large-scale magnetic field. To that end, I had to develop a simple model of the turbulent magnetic field in order to substract its contribution to the Galactic Faraday depth from that of the total magnetic field. I then constructed theoretical maps of Galactic Faraday depth based on a set of analytical models of the large-scale magnetic field that are consistent with various (theoretical and observational) constraints and depend on a reasonable number of free parameters. Finally I fitted the values of these parameters through a challenging optimization phase. My manuscript is divided into four main chapters. In Chapter 1, I present the context of my work as well as various general results useful for my study. In Chapter 2 I review all the elements required for my modeling, with emphasis on the set of analytical models used. In Chapter 3, I describe my simulation and optimization procedures. In Chapter 4 I present my results. In this final chapter, I derive the parameter values of the different field models that lead to the best fit to the observations, I try to identify the role of each parameter and its impact on the theoretical map, and I discuss the different geometries allowed in the various cases. Finally, I show that the fit to the observational map is slightly better with a bisymmetric halo field than with an axisymmetric halo field, and that an X-shape pattern in polarization maps naturally arises in the first case whereas the field appears to remain mainly horizontal in the second case
Livros sobre o assunto "Galaxie : structure"
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De Zeeuw, Tim, ed. Structure and Dynamics of Elliptical Galaxies. Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3971-4.
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Mulder, Pieter Samuel. Structure and kinematics of two nearby disc galaxies. Rijksuniversiteit te Groningen], 1995.
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Jong, Roelof Sybe de, 1965-, ed. Island universes: Structure and evolution of disk galaxies. Springer, 2007.
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1916-, Lin C. C., ed. Spiral structure in galaxies: A density wave theory. MIT Press, 1996.
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Méchéri, Hervé-Frédéric. La galaxie jeunesse: Mémoguide des structures publiques de jeunesse. Institut national de la jeunesse et de l'éducation populaire, 2004.
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Purucker, G. de. Galaxies and solar systems: Their genesis, structure, and destiny. Point Loma Publications, 1987.
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Kamphuis, Peter. The structure and kinematics of halos in disk galaxies. s. n., 2008.
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S, Mulchaey John, Dressler Alan Michael, and Oemler Augustus 1945-, eds. Clusters of galaxies: Probes of cosmological structure and galaxy evolution. Cambridge University Press, 2004.
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Jägers, Willem Joseph. The polarization of radio galaxies: Its structure at low frequencies. Sterrewacht Leiden, 1986.
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Keith, Jahoda, McCammon Dan, and United States. National Aeronautics and Space Administration., eds. The structure of galactic HI in directions of low total column density. National Aeronautics and Space Administration?, 1985.
Encontre o texto completo da fonteCapítulos de livros sobre o assunto "Galaxie : structure"
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Abrams, Bernard, and Michael Stecker. "Galaxies and Galaxy Groups." In Structures in Space. Springer London, 2000. http://dx.doi.org/10.1007/978-1-4471-0441-4_5.
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Peeples, Molly S., and Paul Martini. "Barstrength and Circumnuclear Dust Structure." In Mapping the Galaxy and Nearby Galaxies. Springer New York, 2008. http://dx.doi.org/10.1007/978-0-387-72768-4_106.
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Chiba, Masashi, Hirohito Hayashi, and Motoko Yamada. "Structure and Dynamics of the Old Galactic Components." In Mapping the Galaxy and Nearby Galaxies. Springer New York, 2008. http://dx.doi.org/10.1007/978-0-387-72768-4_8.
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Nishiyama, Shogo, Tetsuya Nagata, and Koji Sugitani. "Structure of the Galactic Bulge and Near Infrared Interstellar Extinction Law." In Mapping the Galaxy and Nearby Galaxies. Springer New York, 2008. http://dx.doi.org/10.1007/978-0-387-72768-4_101.
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Marshall, Douglas J., A. C. Robin, C. Reylé, et al. "Revealing the Three Dimensional Structure of the ISM in the Galaxy." In Mapping the Galaxy and Nearby Galaxies. Springer New York, 2008. http://dx.doi.org/10.1007/978-0-387-72768-4_85.
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Van Der Kruit, P. C. "Structure of Galaxies." In Astrophysics and Space Science Library. Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-0794-5_32.
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Carretero, Conrado, Ignacio Trujillo, and Santiago Patiri. "The Effect of Cosmological Large–scale Structure on the Orientation of Galaxies." In Mapping the Galaxy and Nearby Galaxies. Springer New York, 2008. http://dx.doi.org/10.1007/978-0-387-72768-4_49.
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Yee, H. K. C. "Properties of Galaxies and Galaxy Clusters Associated with Quasars." In Large Scale Structures of the Universe. Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-2995-1_129.
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Yen, David Chien-Chang. "Structure, Evolution and Instability of a Self-gravitating Disk Subject to a Rapidly Rotating Bar." In Mapping the Galaxy and Nearby Galaxies. Springer New York, 2008. http://dx.doi.org/10.1007/978-0-387-72768-4_122.
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Yoshida, Naoki. "Structure of Galactic Dark Halos and Observational Prospects for Identifying the Nature of Dark Matter." In Mapping the Galaxy and Nearby Galaxies. Springer New York, 2008. http://dx.doi.org/10.1007/978-0-387-72768-4_44.
Texto completo da fonteTrabalhos de conferências sobre o assunto "Galaxie : structure"
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Milošević, Stanislav. "KINEMATICAL SIGNATURE OF DWARF GALAXY TIDAL DISRUPTION." In XIV Serbian-Bulgarian Astronomical Conference. Astronomical Observatory, 2024. http://dx.doi.org/10.69646/14sbac23a.
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We can observe stellar structures in a halo of the Milky Way and M31 galaxy (host galaxy). Some of these structures are formed in merger events with dwarf satellite galaxies. With observed velocities in these structures, we can probe different N-body models of dwarf galaxies and run simulations of merger events. In some cases, we can detect the remnant of the dwarf, but sometimes it seems fully disrupted, or it is in the region of the disk, and it is impossible to detect with available resolution. In this work, we investigated the kinematical properties of faint stellar structures and differences in properties of the host galaxy after the merger event. When we cannot detect the remnant of the dwarf, we can find a kinematical trace of the remnant in the kinematical picture of the host.
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Silchenko, O. K. "Galaxies as open systems." In 51-st All-Russian with international participation student scientific conference "Physics of Space". Ural University Press, 2024. http://dx.doi.org/10.15826/b978-5-7996-3848-1.06.
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The galaxy evolution implies permanent change of its main parameters: size, structure, chemical composition of stars, the total stellar mass... Many galaxies proceed their evolution very smoothly. What governs the evolution of galaxies? If does a single physical factor exist which determines all these characteristics? Currently astronomers think that it exists. It is a steady outer cold gas inflow, and its rate and geometry define completely the evolutionary state of a galaxy in every moment of its evolution. To find a source of this outer cold gas is a quite actual problem, unsolved yet.
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Zasov, A., A. Saburova, and O. Egorov. "Sites of star formation in tidal structures." In ASTRONOMY AT THE EPOCH OF MULTIMESSENGER STUDIES. Proceedings of the VAK-2021 conference, Aug 23–28, 2021. Crossref, 2022. http://dx.doi.org/10.51194/vak2021.2022.1.1.172.
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Regions of young stars and emission gas in tidal structures of interacting galaxies are studied on the basis of observationscarried out (jointly with SAO RAS) at BTA telescope. Estimates of the line-of-sight velocities of gas and stars, the oxygenabundance of gas, and the age of stellar population were obtained. On the example of three systems - Arp 305, Arp 194,NGC 90 – we demonstrate the variety of star formation conditions and properties of emission regions outside the stellardisks. In the first two systems, tidal dwarf galaxies were formed. In NGC 90 we found HII regions projecting onto thegalaxy, which differ in velocity by more than 300 kms from the galaxy, and, apparently, emerged in the gas ejected fromthe disk as a result of ram pressure of intergalactic gas.
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Pannikkote, Meghana, Vaidehi S. Paliya, and D. J. Saikia. "UNVEILING GAMMA-RAY-EMITTING FR0 RADIO GALAXIES." In VI Conference on Active Galactic Nuclei and ravitational Lensing. Astronomical Observatory Belgrade, Volgina 7, 11060 Belgrade 38, Serbia, 2024. http://dx.doi.org/10.69646/aob24025.
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Fanaroff-Riley type 0 (FR0) radio galaxies are the latest entry in the jetted active galactic nuclei family. They are characterized by their compact radio morphology and similarities to host galaxy properties of FR I sources. We have recently identified, for the first time, seven gamma-ray emitting FR0s by leveraging the high-resolution radio and optical spectroscopic datasets provided by the ongoing wide-field sky surveys, e.g., the Very Large Array Sky Survey. The subsequent analysis of the multi-wavelength observations reveals the gamma rays to be produced by misaligned jets similar to more common FR I and II radio galaxies. While parsec-scale radio structures vary among FR0s, gamma-ray-detected ones often showcase dominant core emission with core-jet configurations. Further details of the findings will be presented. Unified Astronomy Thesaurus concepts: Fanaroff-Riley radio galaxies (526); BL Lac- ertae objects (158); Relativistic jets (1390); Gammaray sources (633)
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Du, Lun, Zhicong Lu, Yun Wang, Guojie Song, Yiming Wang, and Wei Chen. "Galaxy Network Embedding: A Hierarchical Community Structure Preserving Approach." In Twenty-Seventh International Joint Conference on Artificial Intelligence {IJCAI-18}. International Joint Conferences on Artificial Intelligence Organization, 2018. http://dx.doi.org/10.24963/ijcai.2018/287.
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Network embedding is a method of learning a low-dimensional vector representation of network vertices under the condition of preserving different types of network properties. Previous studies mainly focus on preserving structural information of vertices at a particular scale, like neighbor information or community information, but cannot preserve the hierarchical community structure, which would enable the network to be easily analyzed at various scales. Inspired by the hierarchical structure of galaxies, we propose the Galaxy Network Embedding (GNE) model, which formulates an optimization problem with spherical constraints to describe the hierarchical community structure preserving network embedding. More specifically, we present an approach of embedding communities into a low dimensional spherical surface, the center of which represents the parent community they belong to. Our experiments reveal that the representations from GNE preserve the hierarchical community structure and show advantages in several applications such as vertex multi-class classification and network visualization. The source code of GNE is available online.
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Zasov, A., A. Khoperskov, N. Zaitseva, and S. Khrapov. "When dwarf galaxies turn to be spiral?" In ASTRONOMY AT THE EPOCH OF MULTIMESSENGER STUDIES. Proceedings of the VAK-2021 conference, Aug 23–28, 2021. Crossref, 2022. http://dx.doi.org/10.51194/vak2021.2022.1.1.173.
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Spiral structure is rarely observed in dwarf galaxies because the formation of spiral arms requires special conditions. Weanalyze the sample of about 40 dS-galaxies found among the bright late-type galaxies with M B > −18 m and photometricdiameter D 25 < 12 kpc. These galaxies do not differ statistically from non-dS galaxies apart from the lower average gas (HI)fraction. To check the conditions of formation of spiral structure we carried out a series of direct N-body/hydrodynamicsimulations of dynamic evolution of low-mass stellar/gaseous discs varying the initial parameters of galaxies. We came toconclusion that the gravitational mechanism of formation of spiral structure is effective only for thin stellar/gaseous discs,non-typical for dwarf galaxies. The thicker stellar disc, the more gas is required for the spiral structure to form. The reducedgas content in most dS-galaxies may be a result of more efficient star formation in their relatively thin discs.
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Sheth, Ravi K., Mario Novello, and Santiago Perez. "Large Scale Structure and Galaxies." In COSMOLOGY AND GRAVITATION: XIII Brazilian School on Cosmology and Gravitation (XIII BSCG). AIP, 2009. http://dx.doi.org/10.1063/1.3151838.
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BUSARELLO, G., F. LA BARBERA, P. MERLUZZI, C. HAINES, A. MERCURIO, and M. CAPACCIOLI. "STRUCTURE AND EVOLUTION OF CLUSTER GALAXIES." In Proceedings of the International Conference. WORLD SCIENTIFIC, 2004. http://dx.doi.org/10.1142/9789812702999_0007.
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Fang, Li Zhi. "ORIGIN, STRUCTURE AND EVOLUTION OF GALAXIES." In Proceedings of the Yellow Mountain Summer School. WORLD SCIENTIFIC, 1988. http://dx.doi.org/10.1142/9789814542005.
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Makarov, D., S. Savchenko, A. Mosenkov, et al. "Catalog of edge-on galaxies using the Pan-STARRS1 survey data." In ASTRONOMY AT THE EPOCH OF MULTIMESSENGER STUDIES. Proceedings of the VAK-2021 conference, Aug 23–28, 2021. Crossref, 2022. http://dx.doi.org/10.51194/vak2021.2022.1.1.151.
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We have created a catalog of edge-on galaxies based on the publicly available DR2 data from the Pan-STARRS survey.The intensive use of an artificial neural network has significantly improved the quality of candidate selection. The catalogprovides homogeneous information on astrometry, photometry, and non-parametric morphological statistics for 16551 edge-on galaxies. Our catalog is intended for studying the three-dimensional structure of galaxies with different morphologiesand the scaling relations for disks and bulges.
Relatórios de organizações sobre o assunto "Galaxie : structure"
1
Piacentine, J. Detection of Galaxy Clusters with the XMM-Newton Large Scale Structure Survey. Office of Scientific and Technical Information (OSTI), 2004. http://dx.doi.org/10.2172/833122.
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2
Keller, Christopher J. Analysis of Pacific Enroute Structure in Support of C-5M Super Galaxy. Defense Technical Information Center, 2015. http://dx.doi.org/10.21236/ada619564.
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3
Andersson, K. Complex Structure of Galaxy Cluster Abell 1689: Evidence for a Merger from X-Ray Data? Office of Scientific and Technical Information (OSTI), 2004. http://dx.doi.org/10.2172/826743.
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