This thesis addresses two fundamental questions in astrophysics: (i) To what extent is environment a driver of galaxy evolution? And (ii) How does hierarchical structure formation affect the galaxy environment? The former is addressed by examining the environments of starburst galaxies, the latter by examining clusters undergoing major mergers with focus placed on the efficacy of ??cold fronts?? in identifying systems that have recently undergone a major merger - an essential first step to understanding their impact. For the first of these studies, the 2dFGRS was exploited to select large samples of starburst galaxies. These were used to derive measurements of the local and large-scale environments, clustering properties, and morphologies of starburst galaxies. It is found local environment is most germane in terms of a starburst triggering mechanism, with the starburst galaxies showing an excess of close (<20 kpc) neighbours with comparable luminosity/mass, while 20-30% exhibit a morphology consistent with them being involved in an ongoing tidal/merger interaction. On large scales (5-15 Mpc), the starburst galaxies were found to be much less clustered compared to the overall 2dFGRS population, and were not preferentially found in rich clusters with just over half residing in low to intermediate luminosity groups. However, in a number of cases, evidence for obvious local environmental influences was lacking, indicating starbursts can also be internally driven. For the latter study, the Chandra, archive was used to select a sample of clusters exhibiting ??cold front?? features. Selection required the presence of significant density jumps (>1.5 at the lower 90% CI) in the intracluster medium and for the gas on the denser side of the front to be cooler. From this sample, the clusters Abell 1201, Abell 2163, RXJ1720.1+2638, and Abell 3667 were targeted for comprehensive spectroscopic follow-up at optical wavelengths using the 3.9m Anglo Australian and 6.5m Multiple Mirror Telescopes. Using 321 spectroscopically confirmed members for Abell 1201, 550 for Abell 3667 and 491 for Abell 2163 it is shown that these clusters contain substructure which can be directly related to the cold fronts, whilst for 335 confirmed members in RXJ1720.1+2638 promising evidence exists for merger activity related to the cold front. Despite the range of different types of cold fronts and substructures detected, it is clear that cold fronts are robust signposts of merger activity.

This thesis addresses two fundamental questions in astrophysics: (i) To what extent is environment a driver of galaxy evolution? And (ii) How does hierarchical structure formation affect the galaxy environment? The former is addressed by examining the environments of starburst galaxies, the latter by examining clusters undergoing major mergers with focus placed on the efficacy of ??cold fronts?? in identifying systems that have recently undergone a major merger - an essential first step to understanding their impact. For the first of these studies, the 2dFGRS was exploited to select large samples of starburst galaxies. These were used to derive measurements of the local and large-scale environments, clustering properties, and morphologies of starburst galaxies. It is found local environment is most germane in terms of a starburst triggering mechanism, with the starburst galaxies showing an excess of close (<20 kpc) neighbours with comparable luminosity/mass, while 20-30% exhibit a morphology consistent with them being involved in an ongoing tidal/merger interaction. On large scales (5-15 Mpc), the starburst galaxies were found to be much less clustered compared to the overall 2dFGRS population, and were not preferentially found in rich clusters with just over half residing in low to intermediate luminosity groups. However, in a number of cases, evidence for obvious local environmental influences was lacking, indicating starbursts can also be internally driven. For the latter study, the Chandra, archive was used to select a sample of clusters exhibiting ??cold front?? features. Selection required the presence of significant density jumps (>1.5 at the lower 90% CI) in the intracluster medium and for the gas on the denser side of the front to be cooler. From this sample, the clusters Abell 1201, Abell 2163, RXJ1720.1+2638, and Abell 3667 were targeted for comprehensive spectroscopic follow-up at optical wavelengths using the 3.9m Anglo Australian and 6.5m Multiple Mirror Telescopes. Using 321 spectroscopically confirmed members for Abell 1201, 550 for Abell 3667 and 491 for Abell 2163 it is shown that these clusters contain substructure which can be directly related to the cold fronts, whilst for 335 confirmed members in RXJ1720.1+2638 promising evidence exists for merger activity related to the cold front. Despite the range of different types of cold fronts and substructures detected, it is clear that cold fronts are robust signposts of merger activity.

We study the influence of environment on galaxy evolution by focusing on two galaxy types known for their connection to dense environments, S0s and Brightest Cluster Galaxies (BCGs). Our goal is to identify the mechanisms responsible for the properties of galaxies in groups and clusters. We first examine the effects of environment on S0 formation over the past ~7 Gyr by tracing the increasing S0 fraction in clusters at two mass scales. We find the build-up of S0s driven by groups/clusters with velocity dispersions σ ≲ 750 km s⁻¹, suggesting mechanisms that operate most efficiently via slow encounters (e.g., mergers and tidal interactions) form S0s.With less-massive halos identified as the site for S0 formation, we test whether another route to S0 formation exists, not in isolated groups but rather in a system of four merging groups (SG1120). We place limits on how recent the S0s in that system could have formed, and finding no star formation, conclude they formed ≳ 1 Gyr prior to SG1120's current configuration, when they were in more isolated groups. We next explore cluster outskirts to constrain the number of infalling galaxies that need to be transformed and whether that process has already begun. We find the red fraction of infalling galaxies is elevated relative to the field, and that red galaxies are more clustered than blue ones, a signature of "pre-processing". We disentangle the relative strength of global versus local environment on galaxy transformation by comparing the correlation of red fraction with radius and local density. We find that both parameters are connected with the red fraction of galaxies. Finally, we measure the frequency of galaxies falling into the cluster that are bright enough to supplant the current BCG and compare the results to models. We find in ~ 85% of our clusters that the BCG is secure and remains in its priviledged state until z ~ 0.From these analyses, we find that intermediate density environments (groups and cluster outskirts) are the key site to forming S0 galaxies, and that BCGs, while not exclusively a cluster phenomenon, are well established by the redshifts we explore.

This thesis presents deep photometry of the globular cluster system of the massive elliptical galaxy, M49. Using the C and T1 Washington filters from the MOSAIC camera on the Cerro Tololo Inter-American Observatory 4m telescope, we studied the color, metallicity and luminosity distributions of the globular cluster system. We find a strong bimodality in the color and metallicity distributions of the globular cluster system down to a magnitude of R <24, with 1718 clusters belonging to the blue population and 698 to the red population. In agreement with previous studies, the blue sequence does not exhibit a strong mass-metallicity relation. No difference is found in the mass-metallicity relation between the inner and outer clusters of M49. These results suggest that the mechanism responsible for the mass-metallicity re- lation is not local and may be affected by the galaxy’s individual dynamic history, location in the galaxy cluster and the formation of the globular cluster system itself. We suggest a mechanism based on accretion of gas by proto-clusters as they orbit within their parent dwarf galaxies. The latter would fit the observed behavior of the MMR. / Thesis / Master of Science (MSc)

Mon travail de thèse porte sur l’analyse cosmologique de surveys d’amas de galaxies en rayons X. Les amas sont détectés par le satellite XMM grâce à leur émission X produite par effet Bremsstrahlung du gaz intra-amas. L’étude de la distribution des amas en fonction de leur masse et de leur distance permet de mesurer m, _8 et de contraindre l’équation d’état de l’énergie noire. Une nouvelle approche cosmologique, développée par Clerc et al (2012), se base uniquement sur la distribution de quantités observables en rayons X (flux et couleur). Mon travail a consisté à étendre cette approche en y adjoignant la mesure de la taille apparente de l’émission X des amas. C’est un paramètre qui dépend de la masse de l’amas et de sa distance et qui intervient directement dans la fonction de sélection du survey. J’ai tout d’abord évalué les performances de cette méthode avec une analyse de Fisher. J’ai également étudié l’effet de la dispersion de la relation masse-rayon sur le taux de détection des amas et donc sur les contraintes cosmologiques. Pour valider ces calculs j’ai, dans une seconde partie, utilisé des surveys d’amas X simulés : 100-10000 deg2 à partir d’un modèle purement analytique et 1000 deg2 avec un modèle semi-analytique sur des simulations numériques de matière noire (Aardvark). J’ai déterminé les erreurs sur les paramètres cosmologiques à partir des diagrammes de diagnostic X simuls en utilisant des logiciels de minimisation (MCMC, Amoeba). Ces calculs ont confirmé les prédictions de l’analyse de Fisher. En conclusion, les diagrammes X sont au moins aussi performants que la m´méthode traditionnelle basée sur N(M,z) et d’utilisation beaucoup plus rapide et simple. Je propose quelques applications pour le survey XXL. / Cosmology is one of the fundamental pillars of astrophysics, as such it contains many unsolvedpuzzles. To investigate some of those puzzles, we analyze X-ray surveys of galaxy clusters. These surveys are possible thanks to the bremsstrahlung emission of the intra-cluster medium. The simultaneous fit of cluster counts as a function of mass and distance provides an independent measure of cosmological parameters such as m, _8, and the dark energy equation of state w0. A novel approach to cosmological analysis using galaxy cluster data, called top-down, was developed in N. Clerc et al. (2012). This top-down approach is based purely on instrumental observables that are considered in a two-dimensional X-ray color-magnitude diagram. The method self-consistently includes selection effects and scaling relationships. It also provides a means of bypassing the computation of individual cluster masses. My work presents an extension of the top-down method by introducing the apparent size of the cluster, creating a three-dimensional X-ray cluster diagram. The size of a cluster is sensitive to both the cluster mass and its angular diameter, so it must also be included in the assessment of selection effects. The performance of this new method is investigated using a Fisher analysis. In parallel, I have studied the effects of the intrinsic scatter in the cluster size scaling relation on the sample selection as well as on the obtained cosmological parameters. To validate the method, I estimate uncertainties of cosmological parameters with MCMC method Amoeba minimization routine and using two simulated XMM surveys that have an increasing level of complexity. The first simulated survey is a set of toy catalogues of 100 and 10000 deg2, whereas the second is a 1000 deg2 catalogue that was generated using an Aardvark semi-analytical N-body simulation. This comparison corroborates the conclusions of the Fisher analysis. In conclusion, I find that a cluster diagram that accounts for the fluxes, colors, sizes, and redshifts of the clusters performs well. Additionally, I find that it is at least as efficient as the traditional M,z method for the same cluster samples. I also discuss a proposition to apply this method to the XXL survey data

Galaxy clusters are the largest known gravitationally bound objects, their study is important for both an intrinsic understanding of their systems and an investigation of the large scale structure of the universe. The multi- component nature of galaxy clusters offers multiple observable signals across the electromagnetic spectrum. At X-ray wavelengths, galaxy clusters are simply identified as X-ray luminous, spatially extended, and extragalactic sources. X-ray observations offer the most powerful technique for constructing cluster catalogues. The main advantages of the X-ray cluster surveys are their excellent purity and completeness and the X-ray observables are tightly correlated with mass, which is indeed the most fundamental parameter of clusters. In my thesis I have conducted the 2XMMi/SDSS galaxy cluster survey, which is a serendipitous search for galaxy clusters based on the X-ray extended sources in the XMM-Newton Serendipitous Source Catalogue (2XMMi-DR3). The main aims of the survey are to identify new X-ray galaxy clusters, investigate their X-ray scaling relations, identify distant cluster candidates, and study the correlation of the X-ray and optical properties. The survey is constrained to those extended sources that are in the footprint of the Sloan Digital Sky Survey (SDSS) in order to be able to identify the optical counterparts as well as to measure their redshifts that are mandatory to measure their physical properties. The overlap area be- tween the XMM-Newton fields and the SDSS-DR7 imaging, the latest SDSS data release at the starting of the survey, is 210 deg^2. The survey comprises 1180 X-ray cluster candidates with at least 80 background-subtracted photon counts, which passed the quality control process. To measure the optical redshifts of the X-ray cluster candidates, I used three procedures; (i) cross-matching these candidates with the recent and largest optically selected cluster catalogues in the literature, which yielded the photometric redshifts of about a quarter of the X-ray cluster candidates. (ii) I developed a finding algorithm to search for overdensities of galaxies at the positions of the X-ray cluster candidates in the photometric redshift space and to measure their redshifts from the SDSS-DR8 data, which provided the photometric redshifts of 530 groups/clusters. (iii) I developed an algorithm to identify the cluster candidates associated with spectroscopically targeted Luminous Red Galaxies (LRGs) in the SDSS-DR9 and to measure the cluster spectroscopic redshift, which provided 324 groups and clusters with spectroscopic confirmation based on spectroscopic redshift of at least one LRG. In total, the optically confirmed cluster sample comprises 574 groups and clusters with redshifts (0.03 ≤ z ≤ 0.77), which is the largest X-ray selected cluster catalogue to date based on observations from the current X-ray observatories (XMM-Newton, Chandra, Suzaku, and Swift/XRT). Among the cluster sample, about 75 percent are newly X-ray discovered groups/clusters and 40 percent are new systems to the literature. To determine the X-ray properties of the optically confirmed cluster sample, I reduced and analysed their X-ray data in an automated way following the standard pipelines of processing the XMM-Newton data. In this analysis, I extracted the cluster spectra from EPIC(PN, MOS1, MOS2) images within an optimal aperture chosen to maximise the signal-to-noise ratio. The spectral fitting procedure provided the X-ray temperatures kT (0.5 - 7.5 keV) for 345 systems that have good quality X-ray data. For all the optically confirmed cluster sample, I measured the physical properties L500 (0.5 x 10^42 – 1.2 x 10^45 erg s-1 ) and M500 (1.1 x 10^13 – 4.9 x 10^14 M⊙) from an iterative procedure using published scaling relations. The present X-ray detected groups and clusters are in the low and intermediate luminosity regimes apart from few luminous systems, thanks to the XMM-Newton sensitivity and the available XMM-Newton deep fields The optically confirmed cluster sample with measurements of redshift and X-ray properties can be used for various astrophysical applications. As a first application, I investigated the LX - T relation for the first time based on a large cluster sample of 345 systems with X-ray spectroscopic parameters drawn from a single survey. The current sample includes groups and clusters with wide ranges of redshifts, temperatures, and luminosities. The slope of the relation is consistent with the published ones of nearby clusters with higher temperatures and luminosities. The derived relation is still much steeper than that predicted by self-similar evolution. I also investigated the evolution of the slope and the scatter of the LX - T relation with the cluster redshift. After excluding the low luminosity groups, I found no significant changes of the slope and the intrinsic scatter of the relation with redshift when dividing the sample into three redshift bins. When including the low luminosity groups in the low redshift subsample, I found its LX - T relation becomes after than the relation of the intermediate and high redshift subsamples. As a second application of the optically confirmed cluster sample from our ongoing survey, I investigated the correlation between the cluster X-ray and the optical parameters that have been determined in a homogenous way. Firstly, I investigated the correlations between the BCG properties (absolute magnitude and optical luminosity) and the cluster global proper- ties (redshift and mass). Secondly, I computed the richness and the optical luminosity within R500 of a nearby subsample (z ≤ 0.42, with a complete membership detection from the SDSS data) with measured X-ray temperatures from our survey. The relation between the estimated optical luminosity and richness is also presented. Finally, the correlation between the cluster optical properties (richness and luminosity) and the cluster global properties (X-ray luminosity, temperature, mass) are investigated. / Im Rahmen dieser Arbeit habe ich die 2XMMi/SDSS Galaxienhaufendurchmusterung erstellt (2XMMi/SDSS galaxy cluster survey), eine Suche nach Galaxienhaufen welche auf der Detektion ausgedehnter Röntgenquellen im XMM-Newton Quellenkatalog (2XMMi-DR3) basiert. Die Hauptziele dieser Suche sind die Identifizierung bisher unbekannter röntgenheller Galaxienhaufen, die Erforschung ihrer Beziehungen zwischen Röntgenleuchtkraft und Temperatur (X-ray scaling relation), eine Entdeckung von möglichen weit entfernten Galaxienhaufen und die Beziehung zwischen Eigenschaften im Optischen und Röntgenbereich. Die Durchmusterung ist für alle Quellen der Himmelsregionen ausgelegt, die vom Sloan Digital Sky Survey (SDSS) erfasst werden. Das Ziel besteht darin, ihre optischen Gegenstücke zu finden und deren Rotverschiebungen zu bestimmen. Die gemeinsamen Himmelsareale zwischen XMM-Newton und dem Bildmaterial vom SDSS-DR7 umfassen 210 deg^2. Meine Durchmusterung enthält 1180 mögliche Galaxienhaufen mit wenigstens 80 vom Hintergrund bereinigten Photonen im Röntgenbereich, die einer Qualitätskontrolle erfolgreich standgehalten haben. Um die Rotverschiebungen der möglichen Galaxienhaufen im optischen Bereich zu bestimmen nutzte ich drei Vorgehensweisen: (i) Ein Abgleich jener Kandidaten mit den neuesten und umfangreichsten Katalogen optisch ausgewählter Galaxienhaufen, die in der Literatur verfügbar sind. (ii) Ich entwickelte einen Algorithmus, um Rotverschiebungen der optischen Gegenstücke aus Daten vom SDSS-DR8 zu ermitteln, welches zu photometrischen Rotverschiebungen von 530 Galaxiengruppen-/haufen führte. (iii) Ein weiterer von mir entwickelter Algorithmus nutzte die spektroskopischen Rotverschiebung von roten leuchtkräftigen Galaxien (LRGs) in den Daten des SDSS-DR9 und ergab 324 Gruppen und Haufen. Zusammengefasst enthält diese Probe 574 auch im optischen nachgewiesener Galaxiengruppen und -haufen mit bekannten Rotverschiebungen (0.03 ≤ z ≤ 0.77) - der zur Zeit umfangreichste Katalog von im Röntgenbereich ausgewählten Galaxienhaufen basierend auf aktuellen Röntgenbeobachtungen. Unter jenen Haufen waren ca. 75% im Röntgenbereich nicht bekannt und 40% fanden in der bisherigen Literatur noch keine Erwähnung. Um die Röntgeneigenschaften der im Optischen bestätigten Haufen zu bestimmen, war eine automatische Reduktion und Analyse der Röntgendaten unverzichtbar. Die Prozedur, welche Modelle an die Röntgenspektren anpasste, ergab Temperaturen kT von 0.5 – 7.5 keV für 345 Kandidaten. Für alle Haufen, die auch im optischen auffindbar waren, bestimmte ich die physikalischen Eigenschaften L500 (0.5 x 10^42 – 1.2 x 10^45 erg s^-1) und M500 (1.1 x 10^13 – 4.9 x 10^14 M⊙). Die Probe optisch bestätigter Galaxienhaufen mit gemessenen Rotverschiebungen und Röntgeneigenschaften kann für viele astrophysikalische Anwendungen genutzt werden. Als eine der ersten Anwendungen betrachtete ich die Beziehung zwischen LX - T; das erste Mal für eine so grosse Anzahl von 345 Objekten. Der aktuelle Katalog enthält Gruppen und Haufen, die einen grossen Bereich in Rotverschiebung, Temperatur und Helligkeit abdecken. Der Anstieg jener Beziehung ist im Einklang mit bereits publizierten Werten für nahegelegene Galaxienhaufen von hoher Temperatur und Helligkeit. Nach dem Ausschluss leuchtschwacher Gruppen und der Einteilung der Daten in drei nach Rotverschiebung geordneter Gruppen, waren keine signifikanten Änderungen von Anstieg und intrinsischer Streuung zu beobachten. Als zweite Anwendung unserer Durchmusterung, untersuchte ich die Haufen bezüglich deren Eigenschaften im Optischen und im Röntgenbereich. Zuerst betrachtete ich den Zusammenhang zwischen den Eigenschaften (absolute Helligkeit und optische Leuchkraft) der hellsten Haufengalaxie (BCG) mit denen des Haufens als Ganzem (Rotverschiebung und Masse). Danach berechnete ich die Reichhaltigkeit der Galaxienhaufen und deren optische Leuchtkraft innerhalb von R500 für eine Stichprobe nahegelegener Haufen (z ≤ 0.42, hier sind SDSS Daten noch empfindlich genug um den Grossteil der Haufengalaxien abzubilden) mit gemessenen Röntgentemperaturen. Schlussendlich konnten dieWechselwirkungen zwischen den optischen Eigenschaften (Reichhaltigkeit und Leuchtkraft) und den globalen Eigenschaften (Röntgenleuchtkraft, Temperatur und Masse) näher untersucht werden.

Clusters of Galaxies are amongst the largest gravitationally bound structures in our Universe and consist of thousands of galaxies. It is in these gigantic systems where Brightest Cluster Galaxies (BCGs) are found, the most massive galaxies in our Universe. A BCG, as its name indicates, is the brightest galaxy in a cluster. These enormous galaxies exhibit special properties, suggesting that they experience a different evolutionary path than a normal galaxy. It is widely accepted that their evolution involves merger events, when the BCG accrete another galaxy, as well as interaction events, like tidal stripping and/or removal of star-forming gas. However, the moment when those interactions happen in the life of the BCG and the extent of their impact on the BCG properties are still under discussion. This thesis aims to explore the later stages of BCG evolution by studying the merger/interaction fraction of BCGs in the local Universe. In particular, this research will explore the significance of correlations between the merger/interaction fraction with a variety of BCG properties (Metric Luminosity, α Parameter, BCG distance from the cluster center, BCG offset from the cluster mean redshift) and with a variety of cluster properties (cluster velocity dispersion, luminosity difference between the BCG and the second ranked galaxy in the cluster). The dependence of the merger/interaction fraction on the kinematics of BCGs is also investigated, using data for the BCG stellar velocity dispersion and for the local normalised velocity dispersion of galaxies within 50 kpc of the BCG. To accomplish these analyses, this thesis uses a sample of 432 BCGs at z ≤ 0.08 imaged as part of the Warpfire survey - an all-sky imaging and spectroscopic survey of BCGs in the nearby universe. Interacting and Non Interacting candidates are classified via a visual inspection of the residual images. This classification is performed by three independent people to ensure its robustness and to minimize classification bias. A merger/interaction fraction of fm/i = 0.220 ± 0.025 (stat) ± 0.040 (sys) at z ≤ 0.08 is found, with a lower limit of fmin ≥ 0.07 ± 0.01 (stat) ± 0.04 (sys). Significant correlations between the interaction status of BCG and its Metric Luminosity and α Parameter are also revealed. Specifically, the BCG merger/interaction fraction more than doubles in amplitude from ∼0.2 to ∼0.5 as the α Parameter increases from 0.4 to 0.9. However, those correlations do not appear to alter the Lm – α relationship, which remains robust against BCG interaction status. No significant correlation is found between the interaction status and the location of the BCG in the cluster, nor between the interaction status and the difference between the Metric Luminosity of the BCG and that of the second brightest galaxy in the cluster. However, it is found that BCGs with strong interaction residuals have slightly higher stellar velocity dispersions. Finally, the normalised velocity dispersion of galaxies within 50 kpc of the BCG is found to be lower than the normalised velocity dispersion around random galaxies in the outskirts of the cluster. The results of this thesis clearly indicate ongoing merger activity involving BCGs. The above results are consistent with idea that while BCG stellar accretion is not a dominant process at the current epoch it is not a negligible one either. These results also support a two phased growth model of BCG where the bulk of their stellar mass is assembled prior to z = 0.5 but still continues at a low level today.

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This thesis describes the analysis of pointed thermal Sunyaev-Zel'dovich (SZ) effect data from observations using the Cosmic Background Imager 2 (CBI2). CBI2 is an upgrade to the original Cosmic Background Imager, with antennas that have twice the effective collecting area, and hence provide greater sensitivity on longer baselines. Observations of the thermal SZ effect constrain the line-of-sight integrated gas pressure within clusters of galaxies and, when combined with X-ray data, provide an excellent tool for deriving the physical properties of these large structures. The CBI2 SZ data combine relatively low-resolution with a large field-of-view, and can therefore be used to constrain the gas properties of medium-redshift clusters out to the virial radius. By jointly fitting a suitable analytical model to SZ data and X-ray surface brightness data, it is possible to obtain constraints on the temperature and total mass of the cluster. For the analysis work presented in this thesis I choose to parametrise the gas based upon the known behaviour of the entropy, and the total mass by the Navarro, Frenk and White (NFW) prescription. This model is tested against Hydrodynamic/N-body simulations and is found to reproduce the radial behaviour of key cluster properties. The CBI2 observations presented in this work focus on the REFLEX-DXL clusters, an X-ray luminous sub-sample of the REFLEX survey at z ~ 0.3, which have previously published X-ray surface brightness data. The Bullet Cluster, a significant merger system, is a member of this sample and is presented here as a case study for use of the entropy-based model. The derived total mass and gas mass fraction of this cluster are found to be consistent with results from previous X-ray observations. The derived properties from the REFLEX-DXL sample are used to construct a preliminary set of SZ scaling relations out to the virial radius, and are found to be consistent with the self-similar model for massive clusters.