<p> Globular clusters (GCs) can be divided into two subpopulations when plotted on a colour-magnitude diagram: one red and metal-rich (MR), and the other blue and metal-poor (MP). For each subpopulation, any correlation between colour and luminosity can then be converted into mass-metallicity relations (MMRs).</p> <p> Tracing the MMRs for fifteen GC systems (GCSs) - all around Brightest Cluster Galaxies - we see a nonzero trend for the MP subpopulation but not the MR. This trend is characterised by p in the relation Z=M^p. We find p ~ 0.35 for the MP GCs, and a relation for the MR GCs that is consistent with zero. When we look at how this trend varies with the host galaxy luminosity, we extend previous studies (e.g., Mieske et al, 2006b) into the bright end of the host galaxy sample.</p> <p> In addition to previously presented (B-I) photometry for eight GCSs obtained with ACS/WFC on the HST, we present seven more GCSs. Four of these are newly analysed from HST data, one is previously presented (g-i) photometry obtained with GMOS on Gemini South, and two are the author's newly reduced and analysed (g-i) photometry also obtained with GMOS on Gemini South.</p> <p> Interpretation of these results is important for further understanding the formation and evolution of galaxies within the hierarchical-merging picture, and what process enables the production of two subpopulations.</p> / Thesis / Master of Science (MSc)

We investigate three separate topics associated with the formation and evolution of the stellar mass component in galaxy clusters. The work presented herein is based primarily on optical imaging and spectra taken with, respectively, the Canada-France-Hawaii Telescope and Gemini North/South. We confront the result from the optical data analysis with the results from the analysis of high-resolution X-ray data taken with the Chandra and XMM-Newton space observatories. Confirming earlier results, we find that 22% of brightest cluster galaxies (BCGs) show central inversions in their optical color profiles (blue-cores), indicative of recent star formation or AGN activity. Based on the extended sizes of the blue-core regions we favour recent star formation. Comparison with the host cluster central entropies (and other X-ray properties) demonstrates that the source of cold gas required to fuel the recent activity in BCG cores is direct condensation from the rapidly cooling intra-cluster medium. We measure the giant-to-dwarf ratio (GDR) of red sequence galaxies in a sample of 97 clusters to constrain its evolution over the redshift range 0.05 < z < 0.55. We find that the GDR is evolving and can be parameterized by GDR=(0.88 +/- 0.15)z+(0.44 +/- 0.03). We find that the intrinsic scatter in this relation is consistent with zero, after accounting for measurement error, Poisson noise and contributions from large-scale structure. After correcting for cluster mass effects we investigate the evolution of the individual dwarf and giant populations in order to probe the source of the observed GDR evolution. Beyond z=0.25 the GDR evolution is driven by an increase in the number of dwarfs (consistent with interpretations from the literature), however, below z=0.2 the GDR evolution is caused by a significant reduction in the number of giants. We interpret this a evidence for a significant number of major mergers in the giant population at late times. This is supported by the relatively short dynamical friction timescales for these galaxies. We use velocity-broadened stellar template models to fit the optical spectra of 19 BCGs in order to measure their the line-of-sight component of their central velocity dispersions (sigma). The sigma values are combined with previous measurements of effective radii re and effective surface brightness <I>e to investigate the properties of the BCG fundamental plane. We measure a BCG fundamental plane parameterized by log( re )= alpha log( sigma ) + beta log( <I>e ) + gamma, with best fit parameters alpha = 1.24 +/- 0.08, beta = -0.80 +/- 0.1 and gamma = (0.3 +/- 2.0)x10-4. We constrain the intrinsic scatter in this relation to be deltaint = 0.066 +/- 0.010 in re, consistent with previous measures of the scatter in the fundamental plane for regular cluster ellipticals. Comparing the slope parameters (alpha, beta) of the BCG FP to those from previous studies of the FP for regular cluster ellipticals, we find that there is no conclusive evidence for curvature in the unified FP. We use the sigma measurements to estimate the BCG dynamical masses Mdyn. Comparing these estimates with mass proxies for the clusters (Tx, ng) we find that BCG mass is independent of cluster mass with Mdyn = (2.9 +/- 1.8)x1012 solar masses. / Graduate / 0606 / 0605 / bildfell@uvic.ca

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.

The cores of galaxy clusters contain the most massive galaxies in the Universe, the brightest cluster galaxies. These galaxies are unique compared to their counterpart galaxies outside of clusters as they have much brighter cores, and vast spatially- extended stellar envelopes. The theoretical picture of how they reached their huge masses relied on the idea of gradual stellar mass growth during the second half of the history of the Universe. However, recent observational evidence of highly-overdense protoclusters, the progenitors of these galaxies, demonstrates that some brightest cluster galaxies may have assembled within the first few billion years after the Big Bang – seemingly contradicting our theoretical predictions. I include my theoretical work that shows the short timescales over which these observed protoclusters trans- form into the brightest cluster galaxies and discuss the likelihood of finding these rare protoclusters in the early Universe. To push our understanding of the rapid evolution of these galaxies even further for- ward demands the use of numerical simulations due to the highly coupled, non-linear astrophysical processes that occur during the process. In this dissertation, I include improvements to our numerical models of hydrodynamical turbulence and supermas- sive black holes that I incorporated into a state-of-the-art hydrodynamical+gravity simulation code, in effort to provide the groundwork to improving our understanding of the build-up of the brightest cluster galaxies in the early Universe, and galaxy evolution in general. / Graduate

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