Spelling suggestions: "subject:"largescale 3structure"" "subject:"largescale 1structure""
51 |
Search for Dwarf Emission Line Galaxies in Galaxy VoidsDraper, Christian D 01 August 2019 (has links)
The population and formation of dwarf galaxies, Mr > −14, contain clues about the nature of dark matter. The best place to search for these dwarf galaxies without influence from nearby large galaxies is within galaxy voids, where no galaxies have yet been found. To search for this potential dwarf galaxy population we have developed and applied a new photometric technique. We use three redshifted Ha filters, designated Ha8, Ha12, and Ha16, along with the Sloan broadband filters, g', r', and i' to identify emission line galaxies. From the ratio of the object flux through the Ha filters, Ha12-Ha8 and Ha12-Ha16, we are able to determine the distance to these galaxies and the strength of the emission line captured in the filter set. One problem with using just the three Ha filters is that the system will be sensitive to any emission line which has been redshifted enough to fall within the set. Of particular concern are the [OII] and [OIII] lines which will contaminate the sample. To overcome this we use a color-color relation, g' - r' and r' - i', to help separate which type of emission has been detected. We have applied this method to search for galaxies within the void FN2 and FN8. From this we have found 23 candidate objects which could have Ha emission placing them inside of the void. To better understand the population density dwarf galaxies through voids we have also modeled the population of objects which we will detect having Ha emission compared to the contamination of back ground objects which we can then use to compare the density in the void with the mean galaxy density. We have also begun taking spectra of the emission objects, to ensure our method does detect emission line objects, to test how well the distance and emission strength determination is, and to begin identifying which type of emission we have detected. To date we have taken spectra on 6 objects. All 6 showed emission, 4 with [OII] and 2 with [OIII]. Though none was Ha we formed a “pseudo-redshift” to determine the accuracy of our measurements. This shows that our method is accurate to -127+-204 km/sec.
|
52 |
Cosmologie des théories de gravite modifiées / Formation of large-scale structure in various cosmological scenariosRizzo, Luca Alberto 04 July 2017 (has links)
La cosmologie a atteint une ère passionnante. Pour la première fois dans l’histoire humaine, un modèle quantitatif pour la formation et l’évolution de l’Univers existe,expliquant une gamme très variée de phénomènes et ayant été testé avec une impressionnante. De plus, nous sommes à l’aube d’une époque dans laquelle nous aurons à notre disposition une abondance de données de grande qualité, ce qui nous permettra d’utiliser la cosmologie comme un outil pour tester la physique fondamentale.En particulier, comme les structures de grandes échelles de l’Univers sont gouvernées par la force de gravité, la cosmologie peut être utilisée pour tester la théorie de la relativité générale d’Einstein. Cette idée a inspiré la plupart des travaux décrits dans ce manuscrit, dans lequel j’ai étudié des théories alternatives au modèle standard de la cosmologie et des tests à grandes échelles pour la relativité générale.Dans la première partie de ma thèse, je me suis concentré sur les “théories tenseur-scalaire” de la gravité. Ce sont des théories alternatives de la gravité, dans lesquelles un champ scalaire, qui est responsable de l’accélération de l’expansion de l’Univers, est ajouté à l’action de Einstein-Hilbert. Dans le deuxième chapitre, j’ai décrit le modèle de K-mouflage, une “théorie tenseur scalaire”dans laquelle le champ scalaire possède un terme cinétique non-standard, en montrant son effet non négligeable sur la dynamique des amas des galaxies. J’ai aussi montré comment cet effet peut être utilisé pour contraindre le modèle de “K-mouflage” en utilisant des observations en rayon X.En particulier, j’ai montré que le cisaillement cosmique a un pouvoir assez limité actuellement pour contraindre ces théories, à cause de la faible précision des observations actuelles et des dégénérescences avec les processus baryoniques.Dans le cinquième chapitre, j’ai donné une description de mon étude des relations de cohérence. Ce sont des relations entreles fonctions de corrélation des champs cosmiques à (n + 1) et n points, valables aussi dans le régime non-linéaire.Leur intérêt vient du fait que leur dérivation dépend seulement du Principe d’Équivalence et de l’hypothèse de conditions initiales Gaussiennes, et donc elles peuvent être utilisées pour tester ces hypothèses fondamentales du modèle standard de la cosmologie.Des relations similaires ont été étudiées auparavant, mais j’ai montré comment il est possible d’obtenir des relations qui ne s’annulent pas lorsque tous les champs sont considérés au même instant. J’ai utilisé ce résultat pour obtenir des relations de cohérence entre fonctions de corrélation de quantités observables, notamment le champ de densité des galaxies et la fluctuation de température du fond diffus cosmologie donnée par l’effet Sachs-Wolfe. Ces relations peuvent être utilisées pour des tests de la relativité générale,reposant sur des observations par satellites, sans avoir besoin de modéliser la physique des baryons aux petites échelles.Enfin, j’ai donné un aperçu des quelques perspectives possibles pour poursuivre le travail décrit dans ce manuscrit.En particulier, j’ai souligné comment des simulations numérique sont nécessaires pourmieux comprendre la formation des structuresdans le contexte des modèles “K-mouflage” et“ultra-local”. En outre, elles peuvent être aussiutilisées pour tester les hypothèses sous-tendantl’analyse des lentilles gravitationnelles faiblesprésentée dans ce manuscrit, surtout pourdistinguer l’effet de la physique des baryons etdes neutrinos de l’effet des théories de gravitémodifiée sur le cisaillement cosmique. En cequi concerne les relations de cohérence, uneétude de faisabilité de leur mesure avec les“surveys” cosmologiques est nécessaire, pourcomprendre si elles peuvent donner descontraintes compétitives sur les théoriesalternatives de la gravité. / The study of physical cosmology has reached an exciting era. For the first time in human history, a quantitative model for the formation and the evolution of the Universe exists, which explains a wide range of phenomena and has been tested with incredible accuracy during the last century. Moreover, weare approaching a time when a bounty of high quality cosmological data will be available,allowing us to use cosmology as a tool to test fundamental physics.In particular, as the large-scale structures of the Universe are governed by gravity, cosmology can help us to asses the correctness of Albert Einstein’s general relativity. This idea fueledmost of the work described in this manuscript,in which we study alternative theories to the standard cosmological model and large-scale structure tests for general relativity.In particular, we focus on two scalar-tensor theories of gravity, the K-mouflage models described in Chapter 2 and the ultra-localmodels of gravity presented in Chapter 3. The K-mouflage theories are k-essence models with a non-standard kinetic term that were already studied at the linear and background levels. In this manuscript, we extend this description showing how the scalar field, which is responsible for the late time acceleration of the Universe, has a non-negligible impact on cluster dynamics, arguing that future surveysmay have the power of constraining K-mouflage models via X-ray observations. Next,we study the ultra-local models of gravity,where a scalar field with a negligible kinetic term is added to the Einstein-Hilbert action,investigating how the latter modifiescosmological structure formation and howthese models can be related to super-chameleonmodels.In Chapter 4, we present a cosmic shear data analysis in the context of f (R) and Dilaton models, and we show how current data canaccommodate most of the theories considered,once baryonic and neutrino physicsdegeneracies are taken into account. Finally, in Chapter 5 we present an analysis of consistency relations for large-scale structures,which are non-perturbative relations among correlations of cosmic fields. They are alsovalid in the non-linear regime, where very few analytical results are known, and only rely on the Equivalence Principle and primordial Gaussian initial conditions. This makes them a powerful tool to test general relativity and inflationary models using the cosmologic allarge-scale structures.We provide here the first non-vanishing equaltime consistency relations, which we use to obtain consistency relations involving observational quantities.In this Thesis manuscript, we highlight the major results of the full analysis done in the articles that are appended to the main text,where the reader can quench any thirst for technical details.
|
53 |
Analyse statistique de la distribution des amas de galaxies à partir des grands relevés de la nouvelle génération / Statistical analysis of the galaxy cluster distribution from next generation cluster surveysSridhar, Srivatsan 16 December 2016 (has links)
L'objectif de cette thèse est d'étudier la possibilité de construire la fonction de corrélation à 2 points des amas de galaxies détectés dans les grands relevés optiques de galaxies. En particulier j’étudie l’impact de décalages vers le rouge dégradés car dérivés de données photométriques seules comme cela sera le cas pour les grands relevés à venir. J’ai utilisé des sous-échantillons d’amas sélectionnés dans les catalogues simulés. Les décalages vers le rouge des amas sont modélisés à partir des décalages exacts auxquels sont rajoutés un brui gaussien d’écart type σ (z=0) = 0.005 à 0.050. La fonction de corrélation dans l’espace direct est calculées par une méthode de déprojection. L’étude a été menée sur 4 intervalles de masse et 6 de redshift couvrant le domaine 0<z<2, en s’appuyant dans un premier temps sur les redshifts cosmologiques, puis sur les redshifts bruités. Un accroissement clair de l’amplitude de corrélation avec le redshift et la masse a été trouvé. L’évolution du paramètre de biais b(M,z) est en bon accord avec les prédictions théoriques. La relation d’échelle r0-d est aussi confirmée pour tous les échantillons jusqu’aux plus hauts redshifts et masses. Pour les échantillons bruités il est montré que la fonction de corrélation peut être reconstruite avec une précision de 10% pour σ (z=0) = 0.030. Les paramètres des ajustements ainsi que les biais reconstruits pour tous les bruits envisagés sont compatibles avec le cas non bruité dans un intervalle de 1σ. L’impact de la sélection des échantillons en richesse plutôt qu’en masse est aussi envisagé. Il est montré que Σ(>N200) est similaire à Σ(>masse), ainsi que la fonction de biais qui peut être reproduite à 1σ près. / I aim to study to which accuracy it is actually possible to recover the real-space to-point correlation function from cluster catalogues based on photometric redshifts. I make use of cluster sub-samples selected from a light-cone simulated catalogue. Photometric redshifts are assigned to each cluster by randomly extracting from a Gaussian distribution having a dispersion varied in the range σ (z=0) = 0.005 à 0.050. The correlation function in real-space is computed through deprojection method. Four masse ranges and six redshifts slices covering the redshift range 0<z<2 are investigated, using cosmological redshifts (Zc) and then using photometric redshifts. A clear increase of the corretation amplitude with redshift and mass is found. The evolution of the bias parameter b(M,z) is in fair agreement with the theoretical expectations. The existence of the r0-d relation up to the highest mass, highest redshift sample is tested and is confirmed. It is found that the real-space correlation function can be recovered within and accuracy of 10% for σ (z=0) = 0.030. The best-fit parameters as well as the bias for all σz, are within the 1σ uncertainty of the Zc sample.
|
54 |
Cosmology with cluster-galaxy cross-correlations and topics in assembly biasSalcedo, Andres Nicolas January 2021 (has links)
No description available.
|
55 |
Understanding the Formation of Distant Galaxies in the Context of Large-Scale StructureYun Huang (12456582) 25 April 2022 (has links)
<p> Understanding the formation and evolution of galaxies is one of the most fundamental questions in modern astronomy. While it is widely accepted that galaxy formation needs to be understood in the context of cosmic structure formation of dark matter, a complex interplay of different physical processes that drive galaxy formation makes it challenging to elucidate how the large-scale environment of dark matter influences galaxies, particularly in their formative epoch (z > 2). </p>
<p> As the most luminous nebular emission arising from star formation, Lyalpha provides a promising and effective tool to study the young universe and nascent galaxies.</p>
<p> At z>2, Lyalpha emission is redshifted into the visible window that is detectable by ground-based telescopes. Existing studies also suggest that strong Lyalpha-emitting galaxies represent a young and low-mass galaxy population and therefore are the best visible tracers of the large-scale structure of the distant universe. </p>
<p> In this thesis, I present two complementary studies designed to address these questions using Lyalpha emission as a cosmological tool. In Chapter 2, I investigate the kinematics and spatial distribution of the gas-phase interstellar and circumgalactic media using compact and diffuse Lyalpha emission in and around distant galaxies. I also carry out a comprehensive characterization of how Lyalpha properties correlate with other galaxy properties and the environment that galaxies reside in. In Chapter 3, I explore how Lyalpha-emitting galaxies trace the large-scale structure characterized by other means; I also conduct a detailed investigation of the distribution of different `types' of galaxies and H i gas in and around the most massive cosmic structure known to date. These investigations are informative in building clear expectations for the ongoing and upcoming experiments -- including the Legacy Survey for Space and Time, James Webb Space Telescope, Dark Energy Spectroscopic Instruments, and Hobby-Eberly Telescope Dark Energy eXperiment -- in obtaining a detailed picture of galaxy evolution in the context of their environments. </p>
|
56 |
Systematic errors of cosmological gravity test using redshift space distortion / 赤方偏移空間歪みを用いた宇宙論的重力テストの系統誤差についてIshikawa, Takashi 23 March 2015 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18795号 / 理博第4053号 / 新制||理||1583(附属図書館) / 31746 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 嶺重 慎, 教授 太田 耕司, 准教授 樽家 篤史 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM
|
57 |
Toward a precision cosmological test of gravity from redshift-space bispectrum based on perturbation theory / 宇宙論的な重力テストの精密化に向けた摂動論に基づく赤方偏移空間バイスペクトルの研究Hashimoto, Ichihiko 26 March 2018 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20908号 / 理博第4360号 / 新制||理||1626(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 樽家 篤史, 教授 佐々木 節, 教授 川合 光 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM
|
58 |
Systematics Study and Detection of Baryon Acoustic Oscillations from Future Galaxy Survey and Weak Lensing SurveyDing, Zhejie 05 June 2019 (has links)
No description available.
|
59 |
Cosmic structure formation on small scales: From non-linear galaxy clustering to the interstellar mediumWibking, Benjamin Douglas 17 October 2019 (has links)
No description available.
|
60 |
In Search of Empty Places: Voids in the Distribution of GalaxiesBucklein, Brian K. 06 July 2010 (has links) (PDF)
We investigate several techniques to identify voids in the galaxy distribution of matter in the universe. We utilize galaxy number counts as a function of apparent magnitude and Wolf plots to search a two- or three-dimensional data set in a pencil-beam fashion to locate voids within the field of view. The technique is able to distinguish between voids that represent simply a decrease in density as well as those that show a build up of galaxies on the front or back side of the void. This method turns out to be primarily useable only at relatively short range (out to about 200 Mpc). Beyond this distance, the characteristics indicating a void become increasingly difficult to separate from the statistical background noise. We apply the technique to a very simplified model as well as to the Millennium Run dark matter simulation. We then compare results with those obtained on the Sloan Digital Sky Survey. We also created the Watershed Void Examiner (WaVE) which treats densities in a fashion similar to elevation on a topographical map, and then we allow the "terrain" to flood. The flooded low-lying regions are identified as voids, which are allowed to grow and merge as the level of flooding becomes higher (the overdensity threshold increases). Void statistics can be calculated for each void. We also determine that within the Millennium Run semi-analytic galaxy catalog, the walls that separate the voids are permeable at a scale of 4 Mpc. For each resolution that we tested, there existed a characteristic density at which the walls could be penetrated, allowing a single void to grow to dominate the volume. With WaVE, we are able to get comparable results to those previously published, but often with fewer choices of parameters that could bias the results. We are also able to determine the the density at which the number of voids peaks for different resolutions as well as the expected number of void galaxies. The number of void galaxies is amazingly consistent at an overdensity of −0.600 at all resolutions, indicating that this could be a good choice for comparing models.
|
Page generated in 0.0354 seconds