Dissertations / Theses: 'Galaxy clusters'

1

Bonamigo, Mario. "Triaxial galaxy clusters." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4717/document.

Abstract:

Il est bien établit théoriquement et observationnellement que les amas de galaxies ne sont pas des objets sphèriques, et qu'ils sont beaucoup mieux décrits par la géométrie triaxiale. Malgré cela, les travaux sur la forme tri-dimensionnelle des amas de galaxies sont encore trés rares. L'objet de cette thèse est de contribuer à cette problématique naissante. L'originalité de ce travail est d'aborder ce sujet théoriquement et observationnellement. J'ai mesuré la forme d'amas de galaxies simulés, proposant des prédictions sur la forme des haloes de matière noire. J'ai ensuite développé un algorithme qui se propose de combiner des données en lentilles gravitationnelles et en rayons X afin de contraindre un modèle de haloe triaxial. L'algorithme est testé sur des données simulées. Finalement, je présente l'analyse en rayons X de Abell 1703, qui, combinée avec l'analyse en lentilles gravitationnelles, permettra de déterminer la forme de Abell 1703
It is well established both theoretically and observationally that galaxy clusters are not spherical objects and that they are much better approximated as triaxial objects. This thesis focusses on the three dimencional shape of galaxy clusters. The originality of my approach is to tackle the problem both theoretically and observationally. First, I have measured the shape of dark matter haloes in the Millenium XXL and Sbarbine simulations, providing predictions for dark matter halo shape over 5 order in magnitude in mass. Then, I have developed an algorithm aimed at fitting simultaneously lensing and X-ray data in order to constrain a triaxial mass distribution. The algorithm is tested and characterized on mock data sets. It is found to be able to recover the input parameters. Finally, I present the X-ray analysis of galaxy cluster Abell 1703, which will be combined with the existing lensing analysis in order to investigate its shape

APA, Harvard, Vancouver, ISO, and other styles

2

Eke, Vincent R. "Cosmology with galaxy clusters." Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5195/.

Full text

Abstract:

A number of different ways of using galaxy clusters to provide information concerning fundamental cosmological parameters are considered. Using the observed local cluster X-ray temperature function in conjunction with the Press-Schechter formalism, the normalisation of a CDM power spectrum is found to be σ(_8) = (0.52 ± 0.04)Ω(_o)(^-0.46+0.10Ωo) if Ʌ(_o) = 0 or σ(_8) = (0.52 ± 0.04)Ω(_o)(^-0.52+0.13Ωo) if Ʌ(_o) = 1 — Ω(_0). This result is employed to provide detailed predictions for the abundance of clusters at high redshift, and the differences between predictions for various cosmologies are emphasised. New tests using available high-redshift cluster data are presented. For the adopted power spectrum normalisation, it is found that an Ω(_o) = 0.3, Ʌ(_o) = 0 cosmology vastly overpredicts the number of clusters that were actually found with 0.4 < z < 0.6 in the Extended Medium Sensitivity Survey. The rapid variation in the expected abundance with both σ(_8) and the assumed scatter in the L(_x) – T_x) relation limits the significance of this result, but this model is still ruled out at the ~ 95% confidence level. Order statistics are utilised to calculate the probability of finding extremely massive clusters at high redshifts. With presently available observations, no interesting upper limit can yet be placed on Ω(_o). Systematic variations in the cluster-cluster correlation length calculated using numerical simulations and resulting from the definition of clusters, the chosen σ(_8), the mean intercluster separation and whether or not redshift space distortions are included, are found to exceed the statistical errors on the measurements. Although the uncertainty in ε(_cc) derived from an ensemble of 10 Standard CDM simulations is not sufficient at large separations to remove the discrepancy between this model and results from the APM Cluster Survey, this does suggest that the level at which such a scenario has previously been rejected using ε(_cc) should be significantly reduced. Details and a few tests of a procedure for improving mass and spatial resolution in cosmological simulations are presented. After showing that a coarse-sampling technique can be used to represent the large-scale forces sufficiently accurately, the method is then used to perform ten simulations of clusters forming in an Ω(_o) = 0.3, Ʌ(_o) = 0.7 CDM cosmology. To incorporate non-radiative gas, an SPH code adapted to work on a GRAPEsupercomputer is used. The resulting clusters are found to have virial radii in good agreement with the predictions of the spherical collapse model, dark matter density profiles well described by the 'NFW formula and isothermal central gas components, with temperatures dropping by a factor of ~ 2 near the virial radius. The evolution of these properties is studied as well as that of the bulk quantities describing the clusters, with particular reference to the β parameters relating cluster gas temperatures with virial mass or velocity dispersion. Slightly greater evolution in the luminosity is seen than in previous Ω(_o) = 1 simulations, suggesting that the improved resolution is important. The β parameter relevant to the normalisation of the mass fluctuation spectrum is found to be 0.98 ± 0.07.

APA, Harvard, Vancouver, ISO, and other styles

3

Ruggiero, Rafael. "Galaxy Evolution in Clusters." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-14022019-140755/.

Full text

Abstract:

In this thesis, we aim to further elucidate the phenomenon of galaxy evolution in the environment of galaxy clusters using the methodology of numerical simulations. For that, we have developed hydrodynamic models in which idealized gas-rich galaxies move within the ICM of idealized galaxy clusters, allowing us to probe in a detailed and controlled manner their evolution in this extreme environment. The main code used in our simulations is RAMSES, and our results concern the changes in gas composition, star formation rate, luminosity and color of infalling galaxies. Additionally to processes taking place inside the galaxies themselves, we have also described the dynamics of the gas that is stripped from those galaxies with unprecedented resolution for simulations of this nature (122 pc in a box including an entire 1e14 Msun cluster), finding that clumps of molecular gas are formed within the tails of ram pressure stripped galaxies, which proceed to live in isolation within the ICM of a galaxy cluster for up to 300 Myr. Those molecular clumps possibly represent a new class of objects; similar objects have been observed in both galaxy clusters and groups, but no comprehensive description of them has been given until now. We additionally create a hydrodynamic model for the A901/2 multi-cluster system, and correlate the gas conditions in this model to the locations of a sample of candidate jellyfish galaxies in the system; this has allowed us to infer a possible mechanism for the generation of jellyfish morphologies in galaxy cluster collisions in general.
Nesta tese, nós visamos a contribuir para o entendimento do fenômeno da evolução de galáxias no ambiente de aglomerados de galáxias usando a metodologia de simulações numéricas. Para isso, desenvolvemos modelos hidrodinâmicos nos quais galáxias idealizadas ricas em gás movem-se em meio ao gás difuso de aglomerados de galáxias idealizados, permitindo um estudo detalhado e controlado da evolução destas galáxias neste ambiente extremo. O principal código usado em nossas simulações é o RAMSES, e nossos resultados tratam das mudanças em composição do gás, taxa de formação estelar, luminosidade e cor de galáxias caindo em aglomerados. Adicionalmente a processos acontecendo dentro das próprias galáxias, nós também descrevemos a dinâmica do gás que é varrido dessas galáxias com resolução sem precedentes para simulações dessa natureza (122 pc em uma caixa incluindo um aglomerado de 1e14 Msun inteiro), encontrando que aglomerados de gás molecular são formados nas caudas de galáxias que passaram por varrimento de gás por pressão de arraste, aglomerados estes que procedem a viver em isolamento em meio ao gás difuso de um aglomerado de galáxias por até 300 Myr. Esses aglomerados moleculares possivelmente representam uma nova classe de objetos; objetos similares foram previamente observados tanto em aglomerados quanto em grupos de galáxias, mas um tratamento compreensivo deles não foi apresentado até agora. Nós adicionalmente criamos um modelo hidrodinâmico para o sistema multi-aglomerado A901/2, e correlacionamos as condições do gás nesse modelo com a localização de uma amostra de galáxias jellyfish nesse sistema; isso nos permitiu inferir um possível mecanismo para a geração de morfologias jellyfish em colisões de aglomerados de galáxias em geral.

APA, Harvard, Vancouver, ISO, and other styles

4

Contini, Emanuele. "Galaxy populations in clusters and proto-clusters." Doctoral thesis, Università degli studi di Trieste, 2014. http://hdl.handle.net/10077/9964.

Full text

Abstract:

2012/2013
The aim of my Thesis is to explore the physical properties of the galaxy population in clusters and proto-clusters. A large number of physical processes plays an important role in the formation and evolution of galaxies: cooling, that allows the condensation of gas in the centre of dark matter haloes; star formation, that converts cold gas in stars; feedback from Active Galactic Nuclei (AGN), that prevents the gas in the central regions of haloes from "over-cooling"; feedback from Supernovae, which liberates energy in the surrounding, mixing the gas and enriching it with heavy metals. Galaxy clusters are special environments in which additional important processes take place, and play an important role in the evolution of the cluster galaxy population. Galaxy merging, harassments, tidal interactions, ram pressure stripping and strangulation are all processes acting in dense environments such as clusters of galaxies. I will take advantage of a {\it state of the art}-semi-analytic model of galaxy formation and of a set of 27 high-resolution dark matter only simulations: the semi-analytic model is based on physically motivated and observationally constrained prescriptions for the physical processes listed above and makes use of merger-trees extracted from the simulations to generate mock catalogues of galaxies. First, I make use of this set of simulations to carry out a statistical study of dark matter substructures. In the framework of modern theories of galaxy formation, dark matter substructures can be considered as the birth-sites of luminous galaxies. Therefore, the analysis of subhaloes, and in particular of their mass and spatial distributions, merger and mass accretion histories, provides important information about the expected properties of galaxies in the framework of hierarchical galaxy formation models. I have studied the amount and distribution of dark matter substructures within dark matter haloes, focusing mainly on the measured properties of subhaloes as a function of the mass and physical properties of their parent haloes, and redshift. I show that the fraction of halo mass in substructures increases with increasing mass, reaching $10 \%$ for haloes with mass of the order of $10^{15} \,M_{\odot} \hm$. The scatter in the relation is driven by halo concentration, with less concentrated haloes having larger fractions of mass in substructures. Most of this mass is locateted in the external regions of the parent haloes, in relatively few, but massive subhaloes, thus giving rise to a mass segregation which appears to be stronger at increasing redshift. Tidal stripping is found to be the process responsible for that. In fact, haloes that are more massive at the time of accretion, and that are supposed to host more luminous galaxies, are brought closer to the centre on shorter time-scales by dynamical friction, and therefore suffer of a more significant stripping. The results confirm that the main properties of galaxies, such as luminosity or stellar mass, are related to the mass of subhalos at infall, as found in previous studies.. The main results discussed in this part of the Thesis have been published in Contini et al. (2012), MNRAS.420.2978C. In a second part, I describe the implementation of physical processes responsible for the generation of the Intra-Cluster Light (ICL) in the available semi-analytic model, that, in its original form, does not account for them. The inclusion of these physical processes is, thus, an important improvement of the model. I take advantage of this upgrade of the model to investigate the origin of the ICL and to understand how the main properties of galaxies change with respect to a model that does not include these additional prescriptions. I find the fraction of ICL in groups and clusters predicted by the model to range between $10 \%$ and $40 \%$, with a large scatter and no halo mass dependence. Large part of the scatter on cluster scales is due to a range of dynamical histories, while on smaller scales it is mainly driven by individual accretion events and stripping of relatively massive satellites, with mass of the order of $10^{10.5} \, M_{\odot} \hm$, found to be the major contributors to the ICL. The ICL forms very late, below $ z \sim 1$ and a non negligible fraction (between $5 \%$ and $25 \%$) has been accreted during the hierarchical growth of haloes. Moreover, the ICL is made of stars which cover a relatively large range of metallicity, with the bulk of them being sub-solar, in agreement with recent observational data. The main results of this analysis have been submitted to MNRAS (Contini et al. 2013). In the last part of the thesis, the updated model is used to investigate the properties of the galaxy population in proto-cluster regions. The work is still in progress. I am testing the predictions of the semi-analytic model and comparing them with observations in terms of properties such as galaxy colours, star formation and stellar mass. A preliminary analysis of one very massive proto-cluster region shows that the galaxy population gets red and tend to cluster around the most massive galaxy as time goes by. There are, in literature, only a few attempts to probe such peculiar regions of the Universe from a theoretical point of view. The novelty of this work lies in the connection between massive clusters observed in the local Universe and the proto-cluster regions from which they have formed. I will try to define what a proto-cluster region is, and how it looks like, by studying the main properties of progenitors it contains. Specifically, I will investigate the spatial and velocity distributions of galaxies in simulated proto-clusters, looking at the red and blue galaxy distributions in these regions, as well as at BCG and satellite properties as a function of redshift. The main results of this work will be the subject of a paper in preparation.
XXV Ciclo
1982

APA, Harvard, Vancouver, ISO, and other styles

5

Martinet, Nicolas. "Galaxy clusters : a probe to galaxy evolution and cosmology." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066348/document.

Full text

Abstract:

Cette thèse présente un certain nombre de résultats récents à propos de l'évolution des galaxies et la cosmologie, à partir de l'observation d'amas de galaxies en lumière visible. Nous introduisons d'abord les principales propriétés des amas de galaxies (Chapitre 1.1) et la façon dont ces objets permettent de contraindre le modèle cosmologique standard (Chapitre 1.2). Une grande partie des résultats présentés ici ont été obtenus à partir de l'étude du relevé d'amas DAFT/FADA, qui regroupe des amas dans la gamme de décalages spectraux 0.4
This thesis presents some recent results concerning galaxy evolution and cosmology,based on the observation of galaxy clusters at optical wavelengths. We first introduce the main properties of galaxy clusters (Sect. 1.1) and how they can be used for cosmology within the standard cosmological model (Sect. 1.2). A large fraction of the presented results comes from the study of the DAFT/FADA galaxy cluster survey at redshifts 0.4 < z < 0.9 (Sect. 1.3). We divide our study in two parts according to the observable that is considered: galaxy luminosity or galaxy shape. The distribution of galaxy luminosities is called the galaxy luminosity function (GLF), which can be used to probe the evolution of cluster galaxies (Sect. 2.1). Computing the GLFs for a sub sample of 25 DAFT/FADA clusters, we find that faint blue star forming galaxies are quenched into red quiescent galaxies from high redshift until today. Comparing to the field shows that this transformation is more efficient in high density environments.We also study the fraction of baryons in galaxy groups and clusters (Sect. 2.2). Wefind that in groups, the stars contained in galaxies can reach masses of the same order as those of the intra-cluster gas, while in clusters they are usually negligible relatively to the gas. Taking both stars and gas into account we constrain the matter density parameter Galaxy shapes are distorted by foreground objects that bend light in their vicinity. This lensing signal can be exploited to measure the mass distribution of a foreground cluster. We review the basic theory of weak lensing and shear measurement (Sect. 3.1), and then apply it to a subsample of 16 DAFT/FADA clusters, with Subaru/SuprimeCam or CFHT/MegaCam imaging (Sect. 3.2). We estimate the masses of these clusters, and take advantage of the large fields of view of our images to detect filaments and structures in the cluster vicinity, observationally supporting the hierarchical scenario of cluster growth. Finally, we detect shear peaks in Euclid-like simulations, and use their statistics as a cosmological probe, similarly to cluster counts (Sect. 3.3). We forecast the cosmological constraints that this technique will achieve when applied to the Euclid space mission, and develop a tomographic analysis that adds information from redshifts. We conclude with a discussion of our perspectives on future studies in all the fieldsinvestigated in the present thesis

APA, Harvard, Vancouver, ISO, and other styles

6

Kim, Jae Woo. "Galaxy clustering and galaxy clusters from the UKIDSS DXS." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/3270/.

Full text

Abstract:

Recent wide and deep surveys allow us to investigate the large scale structure of the Universe at high redshift. We present studies of the clustering of high redshift galaxies and galaxy clusters, using reprocessed UKIDSS DXS catalogues. The UKIDSS DXS is one of the deepest near-IR surveys to date and provides sufficient samples of the distant Universe. Firstly we measure the angular correlation function of high redshift red galaxies which are Extremely Red Objects (EROs) and Distant Red Galaxies (DRGs) in Chapters 3 and 4 from DXS SA22 and Elais-N1 fields. We found that their angular correlation functions can be described by a broken power-law. Thus we estimated clustering properties on small and large scales separately. Then we found that red or bright samples are more strongly clustered than those having the opposite characteristics. In addition old, passive EROs are found to be more clustered than dusty, star-forming EROs. The effect of cosmic variance on angular clustering was also investigated. Chapter 5 describes the halo modelling for the angular clustering of EROs. EROs reside in in dark matter haloes having > 1012.9h−1M, and have a bias of 1.93 at z = 1.12 and 3.17 at z = 1.55. From a direct comparison between the observed clustering and the cosmological model, they show good agreement. However the cosmological simulation may predict too many red satellites, especially at high redshfit. In Chapter 6, we present the details of our cluster detection algorithm based on the red sequence technique. This algorithm successfully found published galaxy clusters in the DXS Elais-N1 field. We also found many overdensities in the DXS SA22 field. Two prominent galaxy clusters were confirmed by spectroscopic observations, and we identified a supercluster candidate. Finally the clustering strength of candidate galaxy clusters showed good agreement with previous results and was consistent with the ΛCDM prediction. In the near future the full DXS catalogue will provide an opportunity to detect various high redshift populations. With other advanced surveys, it will be possible to investigate more details of the large scale structure of the Universe.

APA, Harvard, Vancouver, ISO, and other styles

7

Harrison, Ian. "Cosmology with extreme galaxy clusters." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/56777/.

Full text

Abstract:

This thesis describes the use of the rarest high-mass and high-redshift galaxy clusters to constrain cosmology, with a particular focus on the methodology of Extreme Value Statistics (EVS). Motivated by the prospect that even a single sufficiently high mass and high redshift cluster can provide strong evidence against a given cosmology, we first use exact EVS to construct the probability density function (PDF) for the mass of the most-massive cold dark matter (CDM) halo within a fixed redshift volume. We find that the approximation of uncorrelated haloes is valid for high mass haloes 10¹⁵ and large volumes 100⁻¹Mpc, which are also required before the shape of the PDF converges to an asymptotic Generalised Extreme Value (GEV) form. Furthermore, we show the GEV shape parameter γ to be a weak discriminant of primordial non-Gaussianity on galaxy cluster scales. We then extend this analysis to real observations, predicting the PDF for the most-massive galaxy cluster within an observational survey, showing no cluster so far observed is significantly larger than the most-massive expected at its redshift in a concordance cosmology. We also show how the predictions for most-massive cluster with redshift are changed in cosmologies with primordial non-Gaussianity or coupled scalar field dark energy. Finally, we consider why this result appears at odds with some previous analyses, reaffirming that they make use of a biased statistic and showing how an equivalent unbiased one may be constructed. This is then used to rank a comprehensive sample of galaxy clusters according to their rareness, with the cluster ACT-CLJ0102-4915 found to be the most extreme object so far observed. However, the observation of this (and all other clusters so far seen) is shown to be a not unusual event in a concordance universe.

APA, Harvard, Vancouver, ISO, and other styles

8

Gruen, Daniel. "Weak lensing by galaxy clusters." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-183024.

Full text

Abstract:

Der Ursprung und die Entwicklung unseres Universums zeigt sich gleichermaßen in der Raumzeit selbst wie in den Strukturen, die in ihr entstehen. Galaxienhaufen sind das Ergebnis hierarchischer Strukturbildung. Sie sind die massivsten Objekte, die sich im heutigen Universum bilden konnten. Aufgrund dieser Eigenschaft ist ihre Anzahl und Struktur hochgradig abhängig von der Zusammensetzung und Evolution des Universums. Die Messung der Anzahldichte von Galaxienhaufen beruht auf Katalogen, die nach einer beobachtbaren Größe ausgewählt werden. Die Anwendung einer Massen-Observablen-Relation (MOR) erlaubt es, die beobachtete Anzahl als Funktion der Observablen und der Rotverschiebung mit Vorhersagen zu vergleichen und so kosmologische Parameter zu bestimmen. Man kann jedoch zu Recht behaupten, dass diese Messungen noch nicht präzise im Prozentbereich sind. Hauptgrund hierfür ist das unvollständige Verständnis der MOR. Ihre Normalisierung, die Skalierung der Observablen mit Masse und Rotverschiebung und die Größe und Korrelation von intrinsischen Streuungen muss bekannt sein, um Anzahldichten korrekt interpretieren zu können. Die Massenbestimmung von Galaxienhaufen durch die differenzielle Lichtablenkung in ihrem Gravitationsfeld, i.e. durch den so genannten schwachen Gravitationslinseneffekt (weak lensing), kann erheblich hierzu beitragen. In dieser Arbeit werden neue Methoden und Ergebnisse solcher Untersuchungen vorgestellt. Zu ersteren gehören, als Teil der Datenaufbereitung, (i) die Korrektur von CCD-Bildern für nichtlineare Effekte durch die elektrischen Felder der angesammelten Ladungen (Kapitel 2) und (ii) eine Methode zur Maskierung von Artefakten in überlappenden Aufnahmen eines Himmelsbereichs durch Vergleich mit dem Median-Bild (Kapitel 3). Schließlich ist (iii) eine Methode zur Selektion von Hintergrundgalaxien, basierend auf deren Farbe und scheinbarer Magnitude, die eine neue Korrektur für die Kontamination durch Mitglieder des Galaxienhaufens einschließt, im Abschnitt 5.3.1 beschrieben. Die wissenschaftlichen Hauptergebnisse sind die folgenden. (i) Für den Hubble Frontier Field-Haufen RXC J2248.7-4431 bestimmen wir Masse und Konzentration mittels weak lensing und bestätigen die durch Röntgen- und Sunyaev-Zel'dovich-Beobachtungen (SZ) vorhergesagte große Masse. Die Untersuchung von Haufengalaxien zeigt die Abhängigkeit von Morphologie und Leuchtkraft sowie Umgebung (Kapitel 4). (ii) Unsere Massenbestimmung für 12 Galaxienhaufen ist konsistent mit Röntgenmassen, die unter Annahme hydrostatischen Gleichgewichts des heißen Gases gemacht wurden. Wir bestätigen die MOR, die für die Signifikanz der Detektion mit dem South Pole Telescope bestimmt wurde. Wir finden jedoch Diskrepanzen zur Planck-SZ MOR. Unsere Vermutung ist, dass diese mit einer flacheren Steigung der MOR oder einem größen-, rotverschiebungs- oder rauschabhängigen Problem in der Signalextraktion zusammenhängt (Kapitel 5). (iii) Schließlich zeigen wir, durch die Verbindung von Simulationen und theoretischer Modellierung, dass die Variation von Dichteprofilen bei fester Masse signifikant zur Ungenauigkeit von Massenbestimmungen von Galaxienhaufen mittels weak lensing beiträgt. Ein Modell für diese Variationen, wie das hier entwickelte, ist daher wichtig für die genaue Bestimmung der MOR, wie sie für kommende Untersuchungen nötig sein wird (Kapitel 6).
The story of the origin and evolution of our Universe is told, equivalently, by space-time itself and by the structures that grow inside of it. Clusters of galaxies are the frontier of bottom-up structure formation. They are the most massive objects to have collapsed at the present epoch. By that virtue, their abundance and structural parameters are highly sensitive to the composition and evolution of the Universe. The most common probe of cluster cosmology, abundance, uses samples of clusters selected by some observable. Applying a mass-observable relation (MOR), cosmological parameters can be constrained by comparing the sample to predicted cluster abundances as a function of observable and redshift. Arguably, however, cluster probes have not yet entered the era of per cent level precision cosmology. The primary reason for this is our imperfect understanding of the MORs. The overall normalization, the slope of mass vs. observable, the redshift evolution, and the degree and correlation of intrinsic scatters of observables at fixed mass have to be constrained for interpreting abundances correctly. Mass measurement of clusters by means of the differential deflection of light from background sources in their gravitational field, i.e. weak lensing, is a powerful approach for achieving this. This thesis presents new methods for and scientific results of weak lensing measurements of clusters of galaxies. The former include, on the data reduction side, (i) the correction of CCD images for non-linear effects due to the electric fields of accumulated charges (Chapter 2) and (ii) a method for masking artifact features in sets of overlapping images of the sky by comparison to the median image (Chapter 3). Also, (iii) I develop a method for the selection of background galaxy samples based on their color and apparent magnitude that includes a new correction for contamination with cluster member galaxies (Section 5.3.1). The main scientific results are the following. (i) For the Hubble Frontier Field cluster RXC J2248.7--4431 our lensing analysis constrains mass and concentration of the cluster halo and we confirm the large mass predicted by X-ray and Sunyaev-Zel'dovich (SZ) observations. The study of cluster members shows the relation of galaxy morphology to luminosity and environment (Chapter 4). (ii) Our lensing mass measurements for 12 clusters are consistent with X-ray masses derived under the assumption of hydrostatic equilibrium of the intra-cluster gas. We confirm the MORs derived by the South Pole Telescope collaboration for the detection significance of the cluster SZ signal in their survey. We find discrepancies, however, with the Planck SZ MOR. We hypothesize that these are related either to a shallower slope of the MOR or a size, redshift or noise dependent bias in SZ signal extraction (Chapter 5). (iii) Finally, using a combination of simulations and theoretical models for the variation of cluster profiles at fixed mass, we find that the latter is a significant contribution to the uncertainty of cluster lensing mass measurements. A cosmic variance model, such as the one we develop, is necessary for MOR constraints to be accurate at the level required for future surveys (Chapter 6).

APA, Harvard, Vancouver, ISO, and other styles

9

Wilson, Gillian. "Gravitational lensing and galaxy clusters." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/5310/.

Full text

Abstract:

Kaiser & Squires have proposed a technique for mapping the dark matter in galaxy clusters using the coherent weak distortion of background galaxy images caused by gravitational lensing. We investigate the effectiveness of this technique under controlled conditions by creating simulated CCD frames containing galaxies lensed by a model cluster, measuring the resulting galaxy shapes, and comparing the reconstructed mass distribution with the original. Typically, the reconstructed surface density is diminished in magnitude when compared to the original. The main cause of this reduced signal is the blurring of galaxy images by atmospheric seeing, but the overall factor by which the reconstructed surface density is reduced depends also on the signal-to-noise ratio in the CCD frame and on both the sizes of galaxy images and the magnitude limit of the sample that is analysed. We propose a method for estimating a multiplicative compensation factor, f, directly from a CCD frame which can then be used to correct the surface density estimates given by the Kaiser & Squires formalism. We test our technique using a lensing cluster drawn from a cosmological N-body simulation with a variety of realistic background galaxy populations and observing conditions. We conclude that weak lensing observations when calibrated using this method yield not only accurate maps of the cluster morphology but also quantitative estimates of the cluster mass distribution. We then show that weak lensing simulations by rich clusters can be used to constrain the likely range of values of the cosmological constant Ω(_0). Again employing the Kaiser & Squires mass density estimator, we model the lensing induced by a number of simulated clusters from three different cosmologies. We introduce new statistics which are independent of any uncertainties in the surface density mentioned above. We conclude that lensing observations of a small number of clusters should be sufficient to place broad constraints on Ω(_0) and certainly distinguish between the extreme values of 0.2 and 1.We also present deep two-colour photometry of two rich clusters at z = 0.18; A1689 and A665. We use the data to construct number counts as a function of magnitude. To the magnitude depth we were able to probe, we conclude that there is no strong evidence for a steep faint end slope to the galaxy luminosity functioning moderate-redshift clusters.

APA, Harvard, Vancouver, ISO, and other styles

10

Henson, Monique. "Cosmological simulations of galaxy clusters." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/cosmological-simulations-of-galaxy-clusters(c726f7ad-2c0b-4134-9d89-e0b364b07741).html.

Full text

Abstract:

Galaxy clusters are the most massive collapsed structures in the Universe and their properties offer a crucial insight into the formation of structure. High quality observational data is forthcoming with ongoing and upcoming surveys, but simulations are needed to provide robust theoretical predictions for comparison, as well mock data for testing observational techniques. Numerical simulations are now able to accurately model a range of astrophysical processes. This is highlighted in the BAHAMAS and MACSIS simulations, which have successfully reproduced the observed scaling relations of galaxy clusters. We use these simulations to quantify the impact baryons have on the mass distribution within galaxy clusters, as well as the bias in X-ray and weak lensing mass estimates. It is shown that baryons have only a minor affect on the spins, shape and density profiles of galaxy clusters and they have no significant impact on the bias in weak lensing mass estimates. When using spectroscopic temperatures and densities, the X-ray hydrostatic mass bias decreases as a function of mass, leading to a bias of ~40% for clusters with M_500 > 10^15 solar masses. In the penultimate chapter, we use the EAGLE and C-EAGLE simulations to construct more realistic mock cluster observations. The EAGLE simulations have been shown to successfully reproduce the properties of field galaxies and they are complemented by the C-EAGLE project, which extends this work to the cluster scale. We use these simulations to construct a cluster lightcone that accounts for the impact of uncorrelated large scale structure on cluster observables, including weak lensing mass estimates, the Sunyaev-Zel'dovich parameter and X-ray luminosity.

APA, Harvard, Vancouver, ISO, and other styles

11

Farrens, S. "Optical detection of galaxy clusters." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1318077/.

Full text

Abstract:

This thesis first presents a relatively straight forward approach for detecting galaxy clusters using spectroscopic data. A friend-of-friends algorithm based on that of Huchra & Geller (1982) is implemented with linking parameters that take into account selection effects on the the 2dF-SDSS and QSO (2SLAQ) Luminous Red Galaxy Survey (Cannon et al. 2006). The linking parameters are constrained using a mock halo catalogue. The galaxy groups and clusters found with this method have an average velocity dispersion of \sigma v = 467:97 kms-1 and an average size of R clt = 0:78 h-1Mpc. Cluster masses are estimated using the cluster velocity dispersions and appear consistent with values expected for genuine structures. The spectroscopic cluster catalogue is then used to calibrate and compare with a more complex method for detecting clusters using photometric redshifts based on the method of Botzler et al. (2004). The spectroscopic cluster catalogue can be reproduced by around 38% and up to 80% if matching is made only to groups and clusters with six or more members. This code is also applied to the Megaz-LRG DR7 catalogue (Collister & Lahav 2004) producing two catalogues. One that appears to have a good level of completeness relative to the 2SLAQ spectroscopic catalogue. A spectroscopic follow up of some preliminary results from the photometric cluster finder was made using the Anglo-Australian Telescope, which show that the majority of the clusters analysed are genuine and approximate masses can be estimated from the cluster velocity dispersions. Finally, some initials results from on going work in the Dark Energy Survey collaboration are presented, which cover simulated galaxy photometric redshift and colour analysis as well as cluster detection.

APA, Harvard, Vancouver, ISO, and other styles

12

GIORDANO, FABIO. "Gravitational lensing with galaxy clusters." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2010. http://hdl.handle.net/2108/202451.

Full text

Abstract:

Questo lavoro di Tesi esplora alcuni aspetti del lensing gravitazionale su ammassi di galassie. Questi oggetti massivi sono di capitale importanza per la cosmologia e l'astrosica: permettono non solo la derivazione di acuni parametri cosmologici attraverso la loro funzione di massa ma sono anche dei laboratori cosmologici. Un metodo molto promettente di derivare dalle osservazione le distribuzioni di massa degli ammassi è il lensing gravitazionale. La luce emessa da sorgenti di background viene distorta a causa delle alte concentrazioni di massa degli ammassi. L'abbondanza di cluster, la massa totale e i proli di massa devono essere stimati con accuratezza per studiare e discriminare i modelli cosmologici. Il telescopio che abbiamo utilizzato per osservare gli ammassi di galassie è il Large Binocular Telescope (LBT) e le sue Camere (LBC). Mostreremo che questo strumento permette di realizzare accurate analisi di weak lensing: gli specchi primari da 8.4 metri di diametro consentono di ottenere immagini profonde e quindi un'alta densità di galassie di background, necessaria per minimizzare il contributo intrinseco della ellitticità delle sorgenti. Il campo di vista (230×250) delle camere permette di estendere i proli di densità di massa alle regioni più esterne dei clusters e quindi consente di ottenere dati su regioni normalmente inesplorate degli ammassi e rompere la mass-sheet degeneracy. Siccome il weak lensing fornisce informazioni solo su scale angolari ampie, per ottenere un prolo di massa più realistico nel core dei clusters, è necessario utilizzare l'informazione che viene dallo strong lensing se disponibile. Infatti il weak lensing permette una ricostruzione accurata nelle regioni più esterne dei cluster, mentre lo strong lensing è dominante nei core e lì permette un'accurata ricostruzione dei proli di massa. Per cui, mostreremo un metodo non parametrico che combina il weak e lo strong lensing per ottenere un prolo di massa completo per i cluster. Dopo aver descritto i principi del metodo, mostreremo le implementazioni numeriche. I primi test su simulazioni numeriche esplorano l'accuratezza e la realizzabilità del nostro codice e il suo range di applicabilità.
This work explores some aspects of gravitational lensing analyses of clusters of galaxies. These massive gravitationally bound objects in the observable Universe represent the high-mass tail of the mass function, making them objects of capital interest for cosmology. Clusters not only allow for the derivation of several cosmological parameters via their mass function, but they are also cosmic laboratories. A very promising method to derive cluster mass properties from observations is gravitational lensing. Light rays of distant background sources are bent on the way to the observer due to the high mass concentrations of clusters. Therefore, they carry important information about the deectors, which in the clusters' case are important objects for cosmology. The cluster abundance, total mass and mass distribution has to be known very accurately to study and to descriminate cosmological models. The telescope we used to observe galaxy clusters is the Large Binocular Telescope (LBT) and its Cameras (LBC). We will show that this instrument permits to perform accurate weak lensing analyses: the 8.4m primary mirrors allow to obtain deep images and therefore the large numerical density of background sources needed to minimize the intrisic contribute of ellipticity of the sources. The eld of view (23'×250) of the cameras permits to extend the mass density prole to the external regions of the clusters. This allows to get data on tipically unexplored in weak lensing analyses and therefore to no longer suer of the mass-sheet degeracy problem. Since weak lensing yields information only on coarse angular scales, in order to obtain a more realistic mass density prole in the core of clusters we need to use the strong lensing information when available. In fact while weak gravitational lensing allows a reliable reconstruction in the outermost regions of the clusters, strong lensing eects are dominant near the core and permit an accurate mass prole reconstruction in these regions. Hence, we will study a non-parametric method which combines weak and strong gravitational lensing for the reconstruction of the whole mass prole in galaxy clusters. After describing the main principles of our method, we show its numerical implemention. First tests on numerical simulations explore the accuracy and reliability of our code and its range of applicability.

APA, Harvard, Vancouver, ISO, and other styles

13

ANGORA, Giuseppe. "Deep Learning in Galaxy Clusters." Doctoral thesis, Università degli studi di Ferrara, 2022. http://hdl.handle.net/11392/2481663.

Full text

Abstract:

Gli ammassi di galassie hanno un ruolo importante nella cosmologia e nell'astrofisica moderne. Essi figurano come laboratori cosmici nei quali è possibile studiare la formazione e l'evoluzione delle galassie, e migliorare la nostra comprensione della materia oscura usando metodi basati sulla dinamica o su lenti gravitazionali. Come potenti lenti gravitazionali, gli ammassi agiscono da telescopi cosmici estendendo il limite di rilevamento di sorgenti deboli e rivelando galassie lontane. In questo contesto, survey dedicate con il Telescopio Spaziale Hubble (HST) ed estese campagne spettroscopiche hanno fornito dati di straordinaria qualità. Tuttavia, la ricchezza di questi dati non può essere paragonata all'impressionante volume che i futuri telescopi (come Euclid, Vera Rubin Observatory o James Webb Space Telescope) genereranno nei prossimi anni. Il volume e la complessità di questi nuovi dataset possono essere gestiti in modo efficiente con metodi di machine learning e deep learning, che consentono l'esplorazione di correlazioni nascoste all'interno di spazi multidimensionali. Come prima applicazione, abbiamo implementato architetture di deep learning per selezionare i membri di ammassi di galassie, con redshift in 0.2 - 0.6, un primo passo fondamentale per una varietà di studi, come l'evoluzione delle galassie in ambienti densi, stime di massa degli ammassi, modelli di strong lensing. Una volta addestrate con un ampio campione di sorgenti spettroscopicamente confermate (osservazioni VLT VIMOS e MUSE), le reti neurali convolutive (CNN) sono state utilizzate per separare i membri dalle sorgenti di background e foreground, utilizzando solo immagini multi-banda HST, evitando così il complicato e time-consuming processo di estrazione di misure fotometriche. Abbiamo eseguito diversi esperimenti, determinando che le CNN possono classificare i membri con un tasso di purezza-completezza ~90%, mostrando risultati stabili nello spazio dei parametri. Come secondo passo, ci siamo concentrati sull'identificazione dei galaxy-galaxy strong-lenses (GGSL) in ammassi, che possono essere utilizzati per studiare la distribuzione di massa degli ammassi, tracciare la popolazione di sub-aloni attorno ai membri. In questo lavoro, abbiamo optato per una metodologia che combina la necessità di simulare un gran numero di GGSL per addestrare reti neurali, mantenendo la complessità delle osservazioni reali. Abbiamo utilizzato le mappe di deflection angle stimate da modelli ad alta precisione di lensing dell’ammasso, disponibili per 8 cluster (con redshift in 0.2 - 0.6), per simulare migliaia di esempi realistici nelle immagini HST. Abbaimo determinato che le CNN possono rilevare un'ampia frazione di GGSL reali, con un numero limitato di falsi negativi. Abbiamo processato centinaia di membri (spettroscopicamente confermati o selezionati con la CNN), per testare la capacità di generalizzazione delle CNN e per cercare candidati GGSL. Infine, abbiamo implementato uno strumento di cross-correlazione 3D per i dati dello integral field spectrograph MUSE per misurare redshift in modo automatizzato e computazionalmente efficiente. L'estrazione di informazioni spettroscopiche ci consente di costruire dataset per addestrare reti neurali, confermare la membership di galassie, o misurare i redshift della lente e della sorgente in eventi di lensing. Ottimizzato per essere eseguito su processori grafici, questo strumento può elaborare un intero cubo MUSE in poche decine di secondi, cross-correlando 90000 spettri con un set di template. Anche se lo strumento è ancora in fase di sviluppo, i risultati preliminari sembrano piuttosto promettenti e saranno presto applicati di routine sui dati MUSE. Le metodologie sviluppate possono essere estese oltre i dati HST con uno sforzo relativamente modesto e promettono di avere importanti applicazioni per le imminenti survey di prossima generazione.
Galaxy clusters play an important role in modern cosmology and astrophysics. They act as cosmic laboratories where we can study galaxy formation and evolution, and improve our understanding of the nature of Dark Matter using dynamical and gravitational lensing methods. As powerful gravitational lenses, clusters can be used as natural cosmic telescopes thus extending our detection limit of faint sources and revealing the most distant galaxies. In this context, dedicated surveys with Hubble Space Telescope (HST) and ground-based extensive spectroscopic campaigns have provided data with extraordinary quality. The richness of these data sets, however, cannot be compared with the impressive data volume that upcoming surveys (such as Euclid, Vera Rubin Observatory or James Webb Space Telescope) will generate over the next years. The volume and the complexity of these new datasets can be efficiently dealt using machine learning and deep learning methods, which enable the exploration of hidden correlations within a multi-dimensional parameter space. In this thesis, we take advantage of this multidisciplinary tool to enable many scientific investigations of cluster internal structure and background source population. As a first application, we implemented deep learning architectures to select galaxy cluster members in galaxy clusters, in the redshift range 0.2 - 0.6, which is a critical first step for a variety of studies, such as galaxy evolution in dense environments, cluster mass estimates, strong lensing models. By using HST multi-band images alone, convolution neural networks (CNNs) were used to disentangle members from background and foreground sources, once they were trained with a large sample of spectroscopically confirmed sources (VLT VIMOS and MUSE observations), thus avoiding the complicated and time consuming photometric measurement process. We performed several experiments, finding that CNNs can classify members with a purity-completeness rate of ~90%, and showing stable results across the parameter space. As a second step, we focused on the identification of galaxy-galaxy strong lenses (GGSL) in galaxy clusters, which can be used to study the internal mass distribution of clusters, traced by the sub-halo population around cluster member galaxies, and can later be compared with cosmological simulations. In this work, we opted for a methodology that combines the need to simulate a large number of GGSL to train deep neural networks, while maintaining the imaging complexity of real observations. By exploiting high-precision cluster lens models available for 8 clusters (with redshift in 0.2 - 0.6), we used the estimated deflection angle maps to simulate thousands of realistic strong-lenses in real HST. We found that deep networks can detect a large fraction of real GGSLs, with a limited number of false negative events. We processed hundreds of members (spectroscopically confirmed or selected with the CNN), to test deep model generalization capabilities and to search for GGSL candidates. Finally, we implemented a 3D spectroscopy cross-correlation tool on the MUSE integral field spectrograph data to measure redshifts in an automated and computationally efficient fashion. The mining of spectroscopic information allows us to build datasets used to train neural networks, confirm cluster galaxy membership, measure the redshift of lens and source in lensing events. Optimized to be executed on graphic processors, this tool can process an entire MUSE dataset in a few tens of seconds, by cross-correlating 90000 spectra included in the data cube with a sample of spectral templates. Even though the tool is still under development our preliminary results appear rather promising and will soon be applied routinely on MUSE data. The methodologies developed in this thesis can be extended beyond the HST imaging data with a relatively modest effort and promise to have important applications with the upcoming next-generation facilities.

APA, Harvard, Vancouver, ISO, and other styles

14

Braglia, Filiberto Giorgio. "Study of optical properties and galaxy populations of galaxy clusters." Diss., kostenfrei, 2008. http://edoc.ub.uni-muenchen.de/9179/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Wilman, David John. "Galaxy evolution in groups and clusters." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/2816/.

Full text

Abstract:

In this thesis, we investigate the extent to which galaxy evolution is driven by processes common to the group and cluster environments. A bimodality of galaxy properties such as star formation, strongly dependent upon the local overdensity of galaxies, suggests that the passive, early type galaxies common to groups and clusters originate in transformation processes, which are nurtured by the environment. This can only be important to global galaxy evolution if transformations are common in groups, which contain z 50% of the local galaxy population. We present deep Magellan spectroscopy and HST ACS imaging of our group and field samples at 0.3 ˂ z ˂ 0.55, selected from the CN0C2 survey by Carlberg et al. (2001b). We find that these groups contain significantly more passive galaxies than the field, with excesses of S0, elliptical and passive spiral galaxy types. The morphological composition is closely matched to that of irregular and X-ray-faint clusters at a similar epoch. In contrast with a low-redshift group sample selected from 2dFGRS (Eke et al, 2004), we find that the fraction of passive galaxies, fp， is strongly evolving in the group environment, with parallel evolution in the field population. Simple models confirm that galaxy transformations are required to match the evolution of both group and field populations. Qualitatively similar evolution and dependence on environment is found in physically-motivated simulations. However, these do not quantitatively match the environmental nor luminosity dependence in the evolution of fp. We also present a complementary method using photometric redshifts to identify infalling groups in the outskirts of clusters with Wide Field Imaging (WFI) technology. Finally, we identify the key developments which will help to unravel the history of galaxy evolution in coming years.

APA, Harvard, Vancouver, ISO, and other styles

16

Drake, Nick. "Wakes and dynamics of galaxy clusters." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326792.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Rivera, Echeverri José David [UNESP]. "Cosmological analysis of optical galaxy clusters." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152493.

Full text

Abstract:

Submitted by JOSE DAVID RIVERA ECHEVERRI null (josedavidr@ift.unesp.br) on 2018-01-15T19:59:25Z No. of bitstreams: 1 tese_Jose_Rivera.pdf: 8882823 bytes, checksum: 86e911bf64637bfd689e529e9fd65fbe (MD5)
Approved for entry into archive by Hellen Sayuri Sato null (hellen@ift.unesp.br) on 2018-01-16T17:39:58Z (GMT) No. of bitstreams: 1 riveraecheverri_jd_dr_ift.pdf: 8882823 bytes, checksum: 86e911bf64637bfd689e529e9fd65fbe (MD5)
Made available in DSpace on 2018-01-16T17:39:58Z (GMT). No. of bitstreams: 1 riveraecheverri_jd_dr_ift.pdf: 8882823 bytes, checksum: 86e911bf64637bfd689e529e9fd65fbe (MD5) Previous issue date: 2017-12-11
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Os aglomerados de galáxias são os maiores objetos ligados que observamos no universo. Dado que as galáxias são consideradas traçadores de matéria escura, os aglomerados de galáxias nos permitem estudar a formação e a evolução de estruturas em grande escala. As contagens do número de aglomerados de galáxias são sensı́veis ao modelo cosmológico, portanto são usadas como observáveis para restringir os parâmetros cosmológicos. Nesta tese estudamos os aglomerados de galáxias óticos. Iniciamos o trabalho analisando a degradação da precisão e a exatidão no desvio para o vermelho fotométrico estimado através de métodos de aprendizagem de máquina (machine learning) ANNz2 e GPz. Além do valor singular do desvio para o vermelho fotométrico clássico (isto é, valor médio ou máximo da distribuição), implementamos um estimador baseado em uma amostragem de Monte Carlo usando a função de distribuição cumulativa. Mostramos que este estimador para o algoritmo ANNz2 apresenta a melhor concorância com a distribuição do desvio para o vermelho espectroscópico, no entanto, uma maior dispersão. Por outro lado, apresentamos o buscador de aglomerados VT-FOFz, o qual combina as técnicas de Voronoi Tessellation e Friends of Friends. Estimamos seu desempenho através de catálogos simulados. Calculamos a completeza e a pureza usando uma região de cilindrica no espaço 2+1 (ou seja, coordenadas angulares e desvio para o vermelho). Para halos maciços e aglomerados com alta riqueza, obtemos valores elevados de completeza e pureza. Comparamos os grupos de galáxias detectados através do buscador de aglomera- dos VT-FOFz com o catálogo RedMaPPer SDSS DR8. Recuperamos ∼ 90% dos aglomerados de galáxias do catálogo RedMaPPer até o desvio para o vermelho de z ≈ 0.33 considerando galáxias mais brilhantes com r < 20.6. Finalmente, realizamos uma previsão cosmológica usando um método MCMC para um modelo plano de wCDM por meio da abundância de aglomerados de galáxias. O modelo fiducial é um universo ΛCDM plano. Os efeitos devidos à massa observável estimada e aos deslocamentos para o vermelho fotométricos são incluı́dos através de um modelo de auto-calibração. Empregamos a função de massa de Tinker para estimar o número de contagens em uma faixa de massa e um bin de deslocamento para o vermelho. Assumimos que a riqueza e a massa do aglomerado estejam relacionadas através de uma lei de potência. Recuperamos os valores fiduciais com nı́vel de confiança de até 2σ para os testes considerados.
The galaxy clusters are the largest bound objects observed in the universe. Given that the galaxies are considered as tracers of dark matter, the galaxy clusters allow us to study the formation and evolution of large-scale structures. The cluster number counts are sensitive to the cosmological model, hence they are used as probes to constrain the cosmological parameters. In this work we focus on the study of optical galaxy clusters. We start analyzing the degradation of both precision and accuracy in the estimated photometric redshift via ANNz2 and GPz machine learning methods. In addition to the classical singular value for the photometric redshift (i.e., mean value or maximum of the distribution), we implement an estimator based on a Monte Carlo sampling by using the cumulative distribution function. We show that this estimator for the ANNz2 algorithm presents the best agreement with the distribution for spectroscopic redshift, nonetheless a higher scattering. On the other hand, we present the VT-FOFz cluster finder, which combines the techniques Voronoi Tessellation and Friends of Friends. Through mock catalogs, we estimate its performance. We compute the completeness and purity by using a cylindrical region in the 2+1 space (i.e., angular coordinates and redshift). For massive haloes and clusters with high richness, we obtain high values of completeness and purity. We compare the detected galaxy clusters via the VT-FOFz cluster finder with the redMaPPer SDSS DR8 cluster catalog. We recover ∼ 90% of the galaxy clusters of the redMaPPer catalog until the redshift z ≈ 0.33 considering brighter galaxies with r < 20.6. Finally, we perform a cosmological forecasting by using a MCMC method, for a flat wCDM model through galaxy cluster abundance. The fiducial model is a flat ΛCDM Universe. The effects due to the estimated observable mass and the photometric redshifts are included via a self-calibriation model. We employ the Tinker’s mass function to estimate the number counts in a range of mass and a redshift bin. We assume that the richness and the cluster mass are related through a power law. We recover the fiducial values at 2σ confindence level for the considered tests.

APA, Harvard, Vancouver, ISO, and other styles

18

Rivera, Echeverri José David. "Cosmological analysis of optical galaxy clusters /." São Paulo, 2017. http://hdl.handle.net/11449/152493.

Full text

Abstract:

Orientador: Maria Cristina Batoni Abdalla Ribeiro
Coorientador: Filipe Batoni Abdalla
Banca: Filipe Batoni Abdalla
Banca: Laerte Sodré Júnior
Banca: Marcos Vinícius Borges Teixeira Lima
Banca: Martín Makler
Resumo: Os aglomerados de galáxias são os maiores objetos ligados que observamos no universo. Dado que as galáxias são consideradas traçadores de matéria escura, os aglomerados de galáxias nos permitem estudar a formação e a evolução de estruturas em grande escala. As contagens do número de aglomerados de galáxias são sensı́veis ao modelo cosmológico, portanto são usadas como observáveis para restringir os parâmetros cosmológicos. Nesta tese estudamos os aglomerados de galáxias óticos. Iniciamos o trabalho analisando a degradação da precisão e a exatidão no desvio para o vermelho fotométrico estimado através de métodos de aprendizagem de máquina (machine learning) ANNz2 e GPz. Além do valor singular do desvio para o vermelho fotométrico clássico (isto é, valor médio ou máximo da distribuição), implementamos um estimador baseado em uma amostragem de Monte Carlo usando a função de distribuição cumulativa. Mostramos que este estimador para o algoritmo ANNz2 apresenta a melhor concorância com a distribuição do desvio para o vermelho espectroscópico, no entanto, uma maior dispersão. Por outro lado, apresentamos o buscador de aglomerados VT-FOFz, o qual combina as técnicas de Voronoi Tessellation e Friends of Friends. Estimamos seu desempenho através de catálogos simulados. Calculamos a completeza e a pureza usando uma região de cilindrica no espaço 2+1 (ou seja, coordenadas angulares e desvio para o vermelho). Para halos maciços e aglomerados com alta riqueza, obtemos valores elevados de ... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The galaxy clusters are the largest bound objects observed in the universe. Given that the galaxies are considered as tracers of dark matter, the galaxy clusters allow us to study the formation and evolution of large-scale structures. The cluster number counts are sensitive to the cosmological model, hence they are used as probes to constrain the cosmological parameters. In this work we focus on the study of optical galaxy clusters. We start analyzing the degradation of both precision and accuracy in the estimated photometric redshift via ANNz2 and GPz machine learning methods. In addition to the classical singular value for the photometric redshift (i.e., mean value or maximum of the distribution), we implement an estimator based on a Monte Carlo sampling by using the cumulative distribution function. We show that this estimator for the ANNz2 algorithm presents the best agreement with the distribution for spectroscopic redshift, nonetheless a higher scattering. On the other hand, we present the VT-FOFz cluster finder, which combines the techniques Voronoi Tessellation and Friends of Friends. Through mock catalogs, we estimate its performance. We compute the completeness and purity by using a cylindrical region in the 2+1 space (i.e., angular coordinates and redshift). For massive haloes and clusters with high richness, we obtain high values of completeness and purity. We compare the detected galaxy clusters via the VT-FOFz cluster finder with the redMaPPer SDSS DR8 cluster catalog. We recover ∼ 90% of the galaxy clusters of the redMaPPer catalog until the redshift z ≈ 0.33 considering brighter galaxies with r < 20.6. Finally, we perform a cosmological forecasting by using a MCMC method, for a flat wCDM model through galaxy cluster abundance. The fiducial model is a flat ΛCDM Universe. The effects due to the estimated observable mass and (Complete abstract click electronic access below)
Doutor

APA, Harvard, Vancouver, ISO, and other styles

19

Rafferty, Filofteia Laura. "X-ray Bubbles in Galaxy Clusters." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1187802140.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Fedeli, Cosimo. "On strong lensing by galaxy clusters." [S.l. : s.n.], 2007. http://nbn-resolving.de/urn:nbn:de:bsz:16-opus-80858.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Cupani, Guido. "Non equilibrium dynamics of galaxy clusters." Doctoral thesis, Università degli studi di Trieste, 2009. http://hdl.handle.net/10077/3065.

Full text

Abstract:

2007/2008
The thesis is focused on the dynamics of galaxies in the outskirts of galaxy clusters, where the matter is affected by an overall infall motion towards the cluster centre. Starting from the classical results of the spherical collapse model, we determined new theoretical constraints for the mass profile of clusters as a function of the cosmological parameters. We investigated the importance of the turnaround radius (i.e. the radius where the infall motion counterbalances the Hubble expansion motion) as well as the possibility of directly extracting the mass profile from the infall velocity pattern of member galaxies. The theoretical results were applied to a sample of simulated clusters (Borgani et al. 2004, Biviano et al. 2006) to keep the 3-dimensional dynamics under control. We demonstrated that: (1) most clusters are compatible with a single mass profile in the external region (provided their size and mass are normalized to the turnaround scale); (2) it is possible to extract the individual mass profiles of clusters using a selected subset of galaxies identified on their redshift-position distribution; (3) the Jeans equation and the virial theorem must be corrected in the outskirts of clusters to take into account the overall infall motion of matter. Taking advantage of these results, we developed a new technique for estimating the mass profile in cluster outskirts which only relies on the observational properties of member galaxies. This technique turns out to be simpler and more reliable than the current methods and is suitable to be applied to observations.
La tesi è incentrata sulla dinamica delle galassie nelle periferie degli ammassi di galassie, dove la materia è interessata da un moto complessivo di caduta verso il centro dell'ammasso. A partire dai risultati classici del modello di collasso sferico, abbiamo determinato dei nuovi vincoli teorici al profilo di massa degli ammassi in funzione dei parametri cosmologici. Abbiamo analizzato l'importanza del raggio di "turnaround" (ossia il raggio dove il moto di caduta è controblanciato dal moto di espansione di Hubble) e la possibilità di estrarre il profilo di massa direttamente dalla velocità di caduta delle galassie. Abbiamo poi applicato questi risultati teorici a un campione di ammassi simulati (Borgani et al. 2004, Biviano et al. 2006) per tenere sotto controllo la dinamica in tre dimensioni. Con quest'analisi, siamo stati in grado di dimostrare che: (1) la quasi totalità degli ammassi è compatibile con un unico profilo di massa nelle regioni esterne (purché le loro dimensioni e masse siano riscalate rispetto al raggio di turnaround); (2) è possibile estrarre il profilo individuale di un ammasso utilizzando un ristretto sottoinsieme di galassie, identificate dalla distribuzione dei loro redshift e delle loro posizioni; (3) l'equazione di Jeans e il teorema del viriale devono essere corretti nelle periferie degli ammassi in modo da tener conto del moto di caduta della materia. Grazie a questi risultati, abbiamo sviluppato una nuova tecnica per stimare il profilo di massa nelle zone esterne, basata unicamente sulle proprietà osservative delle galassie. Questa tecnica risulta essere più semplice e affidabile degli altri metodi attualmente utilizzati ed è adatta ad essere applicata alle osservazioni.
XXI Ciclo
1981

APA, Harvard, Vancouver, ISO, and other styles

22

Davoli, Guido. "Galaxy-galaxy strong lensing as a probe of the inner structure of galaxy clusters." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13969/.

Full text

Abstract:

La disponibilità di osservazioni profonde di ammassi di galassie, ottenute con telescopi spaziali, ha permesso la scoperta di diversi casi di lensing forte che coinvolgono una galassia d'ammasso e una sorgente retrostante (eventi di galaxy-galaxy strong lensing, GGSL). Ciononostante, questo tipo di eventi sembra essere molto raro nelle più recenti simulazioni idrodinamiche di ammassi di galassie. Questo apparente contrasto fra teoria e osservazioni è uno dei motivi che ci hanno spinto ad indagare sulla fenomenologia degli eventi di GGSL negli ammassi di galassie. Inoltre, lo studio delle sottostrutture presenti negli ammassi è di fondamentale importanza per vincolare le proprietà della materia oscura. In particolare, nella presente tesi abbiamo cercato di verificare la possibile esistenza di un collegamento fra le proprietà fisiche degli ammassi di galassie e la probabilità di osservare eventi di GGSL. Abbiamo quantificato questa probabilità definendo la sezione d'urto per il GGSL. Nel corso del lavoro sono state impiegate simulazioni numeriche di lensing da ammassi di galassie, le cui proprietà rispettano le predizioni del modello cosmologico Lambda-CDM. Nel corso della tesi abbiamo messo in luce come alcune proprietà degli ammassi, quali la pendenza del loro profilo di densità, la funzione di distribuzione radiale e la funzione di massa delle sottostrutture influenzino la sezione d'urto. Questi risultati sono stati confermati quando abbiamo applicato la nostra procedura all'ammasso MACSJ1149. Inoltre, grazie al nostro metodo, abbiamo potuto saggiare la validità di due modelli di massa, ottenuti da un'analisi di lensing forte degli ammassi MACSJ1149 e MACSJ1206, confrontando il numero di eventi di GGSL predetti dai modelli con quelli effettivamente osservati.

APA, Harvard, Vancouver, ISO, and other styles

23

Zenteno, Alfredo. "Galaxy populations in galaxy clusters selected by the Sunyaev-Zeldovich Effect." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-170507.

Full text

Abstract:

We present a study of the galaxy populations in massive galaxy clusters selected by their Sunyaev–Zel’dovich Effect (SZE) signatures. Selection via the SZE is approximately mass- limited where the mass limit varies only slightly with redshift, making it an ideal selection method for studying the evolution of the galaxy content of clusters. We begin by introducing the SZE, the South Pole Telescope (SPT), and the larger research project in which this Thesis is embedded. We then present the core galaxy population studies of this Thesis. In Chapter 3, we present the first large-scale follow-up of an SZE-selected galaxy cluster sample. Of 224 galaxy cluster candidates in the sample, we optically confirm 158 clusters and measure their photometric redshifts. We find a redshift range of 0.1

APA, Harvard, Vancouver, ISO, and other styles

24

Moran, Sean M. Djorgovski S. G. Ellis Richard S. "Understanding the physical processes driving galaxy evolution in clusters : a case study of two z~0.5 galaxy clusters /." Diss., Pasadena, Calif. : California Institute of Technology, 2008. http://resolver.caltech.edu/CaltechETD:etd-08212007-151300.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Ellingson, Erica. "Quasars in galaxy cluster environments." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184878.

Full text

Abstract:

The evolution of radio loud quasars is found to be strongly dependent upon their galaxy cluster environment. Previous studies (Yee and Green 1987) have shown that bright quasars at z ∼ 0.6 are found in clusters as rich as Abell richness class 1, while high luminosity quasars at lower redshifts are found only in poorer environments. An observational study of the environments of 66 low luminosity quasars with 0.3 < z < 0.6 yields several objects in rich clusters of galaxies. This result implies that radio loud quasars in these environments have faded approximately 3 magnitudes in the interval between redshifts 0.6 and 0.4, corresponding to a luminosity e-folding fading time of 900 million years, similar to the dynamical timescale of these environments. The analysis of low luminosity radio quiet quasars indicate that they are never found in rich environments, suggesting that they are a physically different class of objects. Properties of the quasar environment are investigated to determine constraints on the physical mechanisms of quasar formation and evolution. The optical cluster morphology indicates that the cluster cores have smaller radii and higher galaxy densities than are typical for low redshift clusters of similar richness. Radio morphologies may indicate that the formation of a dense intra-cluster medium is associated with the quasars' fading at these epochs. Galaxy colors appear to be normal, but there may be a tendency for clusters associated with high luminosity quasars to contain a higher fraction of gas-rich galaxies than those associated with low luminosity quasars, a result consistent with the formation of an ICM. Multislit spectroscopic observations of galaxies associated with high luminosity quasars indicate that quasars are preferentially located in regions of low relative velocity dispersion, either in rich clusters of abnormally low velocity dispersion, or in poor groups which are dynamically normal. This suggests that galaxy-galaxy interactions may play a role in quasar formation and sustenance. Virialization of rich clusters and the subsequent increase in galaxy velocities may therefore be responsible for the fading of quasars in rich environments.

APA, Harvard, Vancouver, ISO, and other styles

26

Angelinelli, Matteo. "Assessing the turbulent pressure in galaxy clusters." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16340/.

Full text

Abstract:

The amount of turbulent pressure support from residual gas motions at the periphery of galaxy clusters is not well known. In this work, we tested different choices for the filtering of laminar and bulk gas motions from simulated datasets, and we produced new analysis of turbulence in galaxy clusters with a large catalog of cluster simulations. In particular, we have explored the application of different filtering scales for the velocity field, exploring the range from 60 to 600 kiloparsec, in order to disentangle laminar from turbulent motions. We also apply a tailored shocks finding algorithm to minimise their contribution to the estimated turbulent budget. We study the ratio of non-thermal pressure versus total pressure and its radial behavior, finding that it is well described by a simple polynomial formula. The typical non-thermal pressure support we measured in the center of cluster is 3%, while this reaches 10% in the outskirts. We have also compared our results with recent numerical and observational literature. In particular, we found that the different definition of turbulent velocity generates very different amount of turbulent support. As we also discussed in a related paper, the fitting procedure which we used is more statistically significant than the ones presented in literature. Our results allow us to compare with recent observations, and assess which turbulent spatial scale best reproduces the observed trends. We also studied the relations between non-thermal support and cluster’s mass or dynamical state. In particular, our tests have shown that there are not any strong correlations between these quantities. We conclude that our no complete mass selection of the sample affect the study of any possible correlation. Some of the key results of this Thesis are already part of a work which is submitted and will be further documented in a dedicated scientific paper.

APA, Harvard, Vancouver, ISO, and other styles

27

Sijacki, Debora. "Non gravitational heating mechanisms in galaxy clusters." Diss., lmu, 2007. http://nbn-resolving.de/urn:nbn:de:bvb:19-83322.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Lopéz-Cruz, Omar. "Photometric properties of low-redshift galaxy clusters." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27999.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Šijački, Debora. "Non gravitational heating mechanisms in galaxy clusters." kostenfrei, 2007. http://edoc.ub.uni-muenchen.de/8332/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Nastasi, Alessandro. "Multiwavelength Study of high redshift galaxy clusters." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-152323.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Noble, Allison. "Submillimeter imaging of high-redshift galaxy clusters." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86986.

Full text

Abstract:

We present a submillimeter survey of seven high-redshift galaxy clusters, of similar richness and redshift, from the Red-Sequence Cluster Survey (RCS) with the Submillimeter Common-User Bolometric Array (SCUBA) at both 850 and 450 micrometers. The sample consists of three galaxy clusters that exhibit unexpectedly pronounced optical arcs due to strong gravitational lensing, and a control group of four clusters with no apparent strong lensing. Ancillary observations at mid-infrared, radio, optical, and X-ray wavelengths allow for an identification of counterparts to many of the detected submillimeter luminous galaxies (SMGs), which provides redshift constraints and improved astrometry. A tentative excess is seen in the number density of objects within the lensing cluster fields compared to that in the control group. Utilizing photometric redshifts, we conclude that two of the galaxies within the lensing fields are likely cluster members and estimate infrared luminosities of 10^12-10^13 solar luminosities, comparable to that of ultraluminous infrared galaxies (ULIRGs). Such extreme luminosities correspond to intense starbursts with rates of 1000 solar masses per year. We investigate whether the difference in source counts derives from cluster member contamination or enhanced lensing cross-sections, with inconclusive results.
Nous présentons ici un relevé sub-millimétrique de sept amas de galaxies à haute redshift, ayant tous une richesse et un redshift similaire. Ce relevé provient du Red-Sequence Cluster Survey (RCS) pris avec le Submillimeter Common-User Bolometric Array (SCUBA) aux longueurs d'ondes de 850 et 450 micromètres. L'échantillon comprend trois amas de galaxies qui montrent des arcs optiques prononcés et inattendus due à un effet de lentille gravitationnelle forte, et comprend aussi un groupe contrôle de quatre amas n'ayant pas d'effet de lentille apparent. Des observations supplémentaires dans les ondes radio, infrarouge moyennes, optiques et dans les rayons X, permettent l'identification de contreparties pour plusieurs des galaxies sub-millimétrique lumineuses, ce qui restreint la mesure de redshift et améliore l'astrométrie. Nous observons un possible excès de la densité d'objets à l'intérieur des amas avec effet de lentilles par rapport à la densité dans le groupe contrôle. En utilisant les mesures de redshift par photométrie, nous concluons que deux des galaxies à l'intérieur des amas avec effet de lentilles sont des plausibles membres de l'amas et nous estimons des luminosités infrarouges de l'ordre de 10^12-10^13 luminosités solaires, comparable à celle des galaxies infrarouge ultra-lumineuses. De telles luminosités correspondent à une activité de formation stellaire intense avec un taux de 1000 masses solaires par année. Nous étudions également si la différence de densité de sources est due à de la contamination par des membres de l'amas ou à une section efficace d'effet de lentille élargie, sans obtenir de résultats concluants.

APA, Harvard, Vancouver, ISO, and other styles

32

Lane, Kyle P. "Galaxy evolution through clusters and cosmic time." Thesis, University of Nottingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490988.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Sanders, Jeremy Stephen. "Structure in the cores of galaxy clusters." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620444.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

Beasley, Michael Andrew. "Globular clusters as probes of galaxy formation." Thesis, Durham University, 2001. http://etheses.dur.ac.uk/4949/.

Full text

Abstract:

Observations and analysis of globular cluster systems associated with three galaxy types are presented. Spectroscopy of globular cluster (GC) candidates in the Sculptor spirals NGC 253 and NGC 55 has identified 15 GCs in these galaxies. This spectroscopic sample, combined with plate scans, indicates total GC populations consistent with that expected for their luminosity and morphological type. From these data, we define new GC samples for spectroscopy. Radial velocities of 87 GCs in the Virgo elliptical NGC 4472 have been obtained, yielding data for 144 GCs when combined with previous studies. We find the blue GCs have significantly higher velocity dispersion than the red GCs, with little rotation in either population. The GCs dispersion profile declines slowly, yielding mass profiles consistent with X-ray data. We find a steeply rising M/L ratio, indicative of a massive dark halo surrounding this galaxy. From line-strengths of the GCs, we derive ages and metallicities for the GCs using simple stellar population (SSP) models. We find that the GCs are old and coeval and the bimodality seen in then- colours reflects metallicity rather than age differences. The GCs exhibit solar abundance ratios and both subpopulations show evidence for radial metallicity gradients. We have obtained high S/N spectra for 64 star clusters in the Large Magellanic Cloud. We measure their Lick indices to test the age and metallicity calibration of SSP models by comparison with literature values. We find our metallicities are consistent, although the values from our integrated spectra are slightly higher. The agreement of the ages for the old GCs is good, but is somewhat poorer for the youngest clusters. We obtain an age-metallicity relation for the clusters consistent with the galaxy's field stars. We show first results of a project to investigate the age and metallicity distributions of globular cluster systems using semi-analytic models of galaxy formation.

APA, Harvard, Vancouver, ISO, and other styles

35

Mulroy, Sarah Louise. "Illuminating the dark universe with galaxy clusters." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7582/.

Full text

Abstract:

Structure in the Universe formed from tiny density perturbations that grew into the complex cosmic web we see today. At the nodes of this web we find galaxy clusters - the largest gravitationally bound objects ever observed. Their abundance and their properties provide an insight into the evolution of the Universe, so they are important probes of cosmology. Knowledge of their mass is critical for cosmology, but as most of this mass is in the form of dark matter it is a complex measurement, motivating interest in scaling relations between other observables and mass. In this thesis I use a sample of galaxy clusters with high quality multiwavelength observations to investigate these cluster observables and their scaling relations with mass. I find that the easily measured near-infrared and optical cluster luminosities tightly scale with mass, making them promising tools for cosmology with future wide field surveys. I also parameterise scaling relations of observables across a wide range of the electromagnetic spectrum, finding the results to be consistent with self-similarity, in which clusters are formed from a single spherical collapse driven by gravity, and with a closed box picture, in which clusters maintain their baryon budget.

APA, Harvard, Vancouver, ISO, and other styles

36

Del, Pozzo Walter. "Black Holes, Galaxy Clusters and Gravitational Waves." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/1321/.

Full text

Abstract:

This thesis deals with three aspects of modern astrophysical research. We propose a Bayesian data analysis framework to test alternative theories of gravity using observations of Gravitational Waves (GWs) from the inspiral phase of binary systems. We compare General Relativity predictions to the ones from a Massive Graviton theory. We can discriminate between the two theories and produce posterior probability distribution functions. We also devise a method to combine multiple observations that y increases the amount of information that is possible to extract from GWs. Using current wide-field sky survey s, in concert with the established Luminosity -- Black Hole mass relation, we calculate the mass distribution of supermassive massive black holes (SMBHs) and Active Galactic Nuclei (AGNs) in three different environments. SMBHs and radio-AGNs are concentrated in dense environments. The Black Hole Fundamental Plane predicts X-ray properties for our SMBHs and unifies modes of AGN activity in terms of the rate of accretion. Studying two-body mergers of realistic galaxy clusters, we show that these reproduce the observed metallicity distribution in the Intra Cluster Medium (ICM). We characterise entropy generation and mixing induced by the merger process.

APA, Harvard, Vancouver, ISO, and other styles

37

Acebrón, Muñoz Ana. "Cosmography with strong lensing in galaxy clusters." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0256.

Full text

Abstract:

Dans le modèle standard de cosmologie ΛCDM, environ 72% de la densité d'énergie totale de l'Univers se présente sous la forme d'énergie sombre qui causerait la présente accélération de l'Univers. Parmi les sondes cosmologiques couramment utilisées, l'effet de lentille gravitationnel forte dans les amas est une technique prometteuse fournissant des contraintes orthogonales sur les paramètres cosmologiques. Le programme HFF a permis une amélioration significative de l'estimation de la distribution de masse des amas. Cependant, la modélisation de l'effet de lentille forte dans les amas semble ne pas atteindre la résolution angulaire des observations HST. Cette thèse fournit une meilleure compréhension de l'impact des erreurs systématiques dans la modélisation paramétrique de l'effet de lentille forte dans les amas de galaxies et, donc, sur la détermination des paramètres cosmologiques. Premièrement, j'ai analysé deux amas de galaxies simulés, ayant les mêmes caractéristiques que les amas du programme HFF, Ares et Hera. J'ai utilisé plusieurs estimateurs afin d'évaluer la qualité de nos reconstructions obtenues, permettant de quantifier l'impact des erreurs systématiques dues, au choix des profils de densité et configurations et, ensuite, de la disponibilité d'images multiples dans la détermination de paramètres cosmologiques. Deuxièmement, en utilisant deux amas de galaxies, j'ai testé quatre modèles cosmologiques pour lesquels l'équation d'état de l'énergie sombre, w(z), est paramétrisée en fonction du redshift. J'ai réalisé plusieurs modélisations pour quantifier l'impact des erreurs systématiques liées à la position des images multiples sur les paramètres cosmologiques
In the standard cosmological model ΛCDM, about 70% of the energy density of the Universe is in the form of a dark energy that would cause the current acceleration of the Universe. Among the extensively used cosmological probes, using strong lensing features in galaxy clusters is a promising technique yielding orthogonal constraints on cosmological parameters. The program HFF has led to a significant improvement of cluster mass estimates. However, strong lensing modelling appears to be still unable to match the HST observations angular resolution.This thesis provides a better understanding of how systematic errors impact the retrieval of cosmological parameters in order to use strong lensing clusters as reliable cosmological probes. Firstly, I have analyzed two simulated HFF-like clusters, Ares and Hera, I use several estimators to assess the goodness of our reconstructions by comparing our multiple models, with the input models. This allows to quantify the impact of systematic errors arising from the choice of different density profiles and configurations and, secondly, from the availability of constraints in the parametric modelling of strong lensing clusters and therefore on the retrieval of cosmological parameters. Secondly, I probe four cosmological models in which the equation of state of dark energy, w(z), is parameterized as a function of redshift using strong lensing features in two galaxy clusters. To quantify how the cosmological constraints are biased due to systematic effects in the strong lensing modelling, I carry out several modelling attempts considering different uncertainties for the multiple images positions

APA, Harvard, Vancouver, ISO, and other styles

38

Makda, Nazir Ahmed Adam. "Ultra-diffuse galaxy candidatesin stripe 82 clusters." Master's thesis, Faculty of Science, 2019. https://hdl.handle.net/11427/31737.

Full text

Abstract:

The evolution of galaxies in the cluster environment is a complex process, with many outstanding questions. A wide range of galaxy morphologies, colours, sizes and luminosities are found in clusters, the least studied of which are the faint galaxy populations. Studying the faint end of the galaxy luminosity distribution may provide a valuable insight into the evolution of galaxies in cluster environments. The largest of these faint galaxies are classified as Ultra-Diffuse galaxies (UDGs). UDGs are low surface brightness galaxies with a very low stellar mass component, however they have sizes comparable to the Milky Way. These galaxies are hard to detect and classify as they are very faint. To survive in the cluster environments, where they have been observed, these galaxies must contain significant amounts of dark matter as the strong tidal fields would normally tear diffuse low-mass galaxies apart. The high abundance of UDGs in clusters has only recently been recognized, therefore identifying and measuring their properties is key to understanding how they are formed and continue to exist. In this thesis, I search for low surface brightness galaxies, spanning from typical dwarf galaxies to UDGs, in 16 low redshift (z< b/a >= 0.52. The number of faint galaxies in clusters follows a power-law with respect to the cluster halo mass, N ∝ M1.05±0.45, determined through bootstrap resampling. This shows that the number of UDG candidates increases as the cluster halo mass increases.

APA, Harvard, Vancouver, ISO, and other styles

39

Pike, Simon Robert. "Simulations of galaxy clusters with AGN feedback." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/simulations-of-galaxy-clusters-with-agn-feedback(02c5a9f6-03ad-4c80-9e7c-832db83998d8).html.

Full text

Abstract:

Clusters of galaxies provide a unique opportunity to simultaneously study cosmology through low scatter scaling relations and the complex baryonic physics that occurs in cluster cores. As such it is of key importance to quantify the effects of the various physical processes that drive cluster evolution. In this thesis a sample of 30 clusters from the Millennium Gas Simulation, of masses 10^14/h Solar Masses < M200 < 10^15/h Solar Masses, were selected and run at a higher resolution using the re-simulation technique, using a modified version of Gadget-2, an N-body SPH code. Each cluster was run multiple times with increasing levels of sub-grid physics in order to separate the different effects that govern cluster evolution. The models implemented starting with non-radiative (NR), simulations then added cooling and star formation (CSF), supernova feedback (SFB) and AGN feedback model (AGN) respectively. In order to best match observations a study of supernova and AGN feedback parameters was conducted. The sample of clusters were also used to quantify the magnitude of biases created when observing clusters, in an attempt to classify the accuracy of these measurements of clusters. Additionally, the effects of the biases were also included in the estimation of the cluster mass using hydrostatic equilibrium. The best match to the observed gas, star and baryon fractions, scaling relations and gas profiles was found when powerful supernova feedback was included, which heats gas particles to 10^7K, and an AGN model whose heating temperature scales with the final virial temperature of the cluster, so that particles in a 10^14/h Solar masses and 10^15/h Solar Masses cluster are heated to 10^8K and 10^8.5 K respectively. Outside the core, this model successfully matches all the observed profiles and scaling relations excluding the spectrascopic-like temperature. The core region is simulated with come success, with pressures matching those observed but gas that is too cool and dense, resulting in an inability to reproduce the non cool core entropy profiles. Cold dense gas is more heavily weighted in the spectrascopic-like temperature, allowing significant contributions from gas in substructures and cold dense clumps of gas that are un-ascociated with any substructures and seems to be an artificial construct of SPH. When this gas is removed using the method outlines in \cite{Roncarelli2006}, temperatures outside the core match observations, but the core region is still too dense and cool. Clearly this core region requires more complex physics, possibly through implementation of an improved SPH code or more complex sub-grid physics such as that associated with the AGN feedback. The bias profiles also exhibit a similar sensitivity to the cool dense gas clumps, having a profound effect on the observed profiles and creating significant scatter in the mass estimated using hydrostatic equilibrium. Removing this cold dense gas using the Roncarelli method results in reduced biases and hydrostatic mass estimates closer to the true values. The resulting scaling relations and profiles including the effects of biases differ from those without the biases, but not significantly. It is clear that biases can affect the observed profiles and scaling relations, but this effect is minimised by excluding the coldest densest gas. As the choice of how much gas is removed is somewhat arbitrary, it is clear that further work in this field would require better SPH implementations that do not produce the erroneous dense gas clumps and the generation of mock observations using the simulated data.

APA, Harvard, Vancouver, ISO, and other styles

40

Millington, S. J. C. "Clusters of galaxies." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382461.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Helsdon, Stephen Farrell. "X-ray properties of galaxy groups." Thesis, University of Birmingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289717.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Cluver, Michelle E. "Probing distant clusters : a pre-SALT photometric study of intermediate redshift galaxy cluster." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/4415.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Cuciti, Virginia <1989&gt. "Cluster-scale radio emission: analysis of a mass-selected sample of galaxy clusters." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/8540/1/Tesi_PhD.pdf.

Full text

Abstract:

Radio halos are Mpc scale diffuse sources located at the center of a fraction of galaxy clusters. In the current theoretical picture, they form via the re-acceleration of electrons in the ICM by means of turbulence, injected during cluster mergers. This scenario allows basic predictions on the formation history of radio halos that can only be tested by analysing large samples of galaxy clusters with adequate radio and X-ray data. The main goal of this Thesis is to study the first complete large sample of mass-selected galaxy clusters to obtain solid statistical constraints on the connection between radio halos and the dynamics and mass of the host clusters. We used the Planck SZ catalogue to select a sample of 75 massive galaxy clusters (M500>6x10^{14}Msun) at redshift z=0.08-0.33 and we collected information on the presence or absence of diffuse emission from the literature and from the large observational (GMRT and JVLA) campaign carried out during this PhD project. We analysed X-ray Chandra and XMM-Newton data to investigate the dynamical properties of clusters. We updated the radio power-mass scaling relation for radio halos and we found clear evidence for a bimodal behaviour of clusters in both the radio power-mass plane and, for the first time, in the radio emissivity-mass diagram, with radio halos and non-radio halo clusters following two distinct distributions. Similarly to previous studies, we found that this bimodality is clearly connected to the cluster dynamics. For the very first time, we found an increase of the radio halo fraction with the cluster mass, which is remarkably in agreement with theoretical models. In addition to the statistics of radio halos, the amount of data available in this Thesis led to the discovery of new radio relics, mini halos and head tail radio galaxies in our clusters.

APA, Harvard, Vancouver, ISO, and other styles

44

Spurgeon, Louise Elizabeth. "XMM and ROSAT observations of clusters of galaxies." Thesis, University of Leicester, 2003. http://hdl.handle.net/2381/30665.

Full text

Abstract:

I present an investigation into the X-ray properties of galaxy clusters, consisting of a principal component analysis of ROSAT data and studies of three clusters observed with the XMM-Newton satellite. The principal component analysis provides an investigation into similarities between cluster surface brightness profiles. Initial results for 42 clusters are presented and compared to existing models. The cluster profiles are reproduced to good accuracy using three principal components. Correlation of the principal components to physical properties is investigated but the results are inconclusive. Observations of Abell 1413, Abell 665 and Abell 2163 made with XMM-Newton were investigated spectrally and spatially to determine cluster properties. Global temperatures were found to be 7.08 +/- 0.140.13 keV for Abell 665 and 11.98 +/- 1.2 keV for Abell 2163. The temperature and abundance profiles of the clusters are very different, with some differences attributed to the recent merging of subclusters in Abell 665 and Abell 2163. Spatial analysis of the cluster surface brightness profiles is undertaken with beta and NFW models. The profiles produced for the three clusters are used to estimate the variation of gas, gravitational and iron mass with radius. These are used to draw general conclusions, such supernovae numbers (NSNII 109--11). The cosmological density and matter density parameters are found; &OHgr;0 = 0.22 -- 0.33 +/- 0.1 and &OHgr; m ? 0.12+/-0.060.04. This suggests a low density universe, but is subject to uncertainty due to extrapolation to larger radii.

APA, Harvard, Vancouver, ISO, and other styles

45

Rebusco, Paola. "Impact of supermassive black holes on galaxy clusters." Diss., [S.l.] : [s.n.], 2007. http://edoc.ub.uni-muenchen.de/archive/00006900.

Full text

APA, Harvard, Vancouver, ISO, and other styles

46

Zibetti, Stefano. "Diffuse stellar components in galaxies and galaxy clusters." Diss., lmu, 2004. http://nbn-resolving.de/urn:nbn:de:bvb:19-30331.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Makiya, Ryu. "Cosmic-Ray Acceleration in Galaxies and Galaxy Clusters." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/175125.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Mana, Annalisa. "Optically selected galaxy clusters as a cosmological probe." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-163279.

Full text

Abstract:

Multi-wavelength large-scale surveys are currently exploring the Universe and establishing the cosmological scenario with extraordinary accuracy. There has been recently a significant theoretical and observational progress in efforts to use clusters of galaxies as probes of cosmology and to test the physics of structure formation. Galaxy clusters are the most massive gravitationally bound systems in the Universe, which trace the evolution of the large-scale structure. Their number density and distribution are highly sensitive to the underlying cosmological model. The constraints on cosmological parameters which result from observations of galaxy clusters are complementary with those from other probes. This dissertation examines the crucial role of clusters of galaxies in confirming the standard model of cosmology, with a Universe dominated by dark matter and dark energy. In particular, we examine the clustering of optically selected galaxy clusters as a useful addition to the common set of cosmological observables, because it extends galaxy clustering analysis to the high-peak, high-bias regime. The clustering of galaxy clusters complements the traditional cluster number counts and observable-mass relation analyses, significantly improving their constraining power by breaking existing calibration degeneracies. We begin by introducing the fundamental principles at the base of the concordance cosmological model and the main observational evidence that support it. We then describe the main properties of galaxy clusters and their contribution as cosmological probes. We then present the theoretical framework of galaxy clusters number counts and power spectrum. We revise the formulation and calibration of the halo mass function, whose high mass tail is populated by galaxy clusters. In addition to this, we give a prescription for modelling the cluster redshift space power spectrum, including an effective modelling of the weakly non-linear contribution and allowing for an arbitrary photometric redshift smoothing. Some definitions concerning the study of non-Gaussian initial conditions are presented, because clusters can provide constraints on these models. We dedicate a Chapter to the data we use in our analysis, namely the Sloan Digital Sky Survey maxBCG optical catalogue. We describe the data sets we derived from this large sample of clusters and the corresponding error estimates. Specifically, we employ the cluster abundances in richness bins, the weak-lensing mass estimates and the redshift-space power spectrum, with their respective covariance matrices. We also relate the cluster masses to the observable quantity (richness) by means of an empirical scaling relation and quantify its scatter. In the next Chapter we present the results of our Monte Carlo Markov Chain analysis and the cosmological constraints obtained. With the maxBCG sample, we simultaneously constrain cosmological parameters and cross-calibrate the mass-observable relation. We find that the inclusion of the power spectrum typically brings a 50% improvement in the errors on the fluctuation amplitude and the matter density. Constraints on other parameters are also improved, even if less significantly. In addition to the cluster data, we also use the CMB power spectra from WMAP7, which further tighten the confidence regions. We also apply this method to constrain models of the early universe through the amount of primordial non-Gaussianity of the initial density perturbations (local type) obtaining consistent results with the latest constraints. In the last Chapter, we introduce some preliminary calculations on the cross-correlation between clusters and galaxies, which can provide additional constraining power on cosmological models. In conclusion, we summarise our main achievements and suggest possible future developments of research.

APA, Harvard, Vancouver, ISO, and other styles

49

Winkworth, Carolyn Louise. "An Observational Study of High Redshift Galaxy Clusters." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520307.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Castander, Francisco Javier. "X-ray studies of high redshift galaxy clusters." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627485.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Galaxy clusters'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles