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Star formation rates and morphologies of galaxies, particularly low-mass galaxies, are strongly linked to the properties of their environment. Using a large sample of galaxies in SDSS groups, we investigate the dependence of star formation and morphology on host properties such as the X-ray luminosity and dynamical state, while controlling for stellar and halo mass. We find that galaxy populations in groups with strong X-ray emission have preferentially low star-forming and disc fractions, both within and beyond the radius associated with the X-ray emission. Additionally, we consider the effect of group dynamics on the properties of member galaxies and the infalling galaxy population separately. We show that the fraction of both star-forming and disc galaxies are independent of dynamical state for galaxies at large group-centric radii, while galaxies within the inner regions of the halo are sensitive to the dynamical state of their host group. Specifically, low-mass galaxies in unrelaxed groups show higher star-forming -- though no difference is detected when considering disc fractions. Together these findings help constrain the mechanisms at play in environmentally driven galaxy evolution.

We investigate the mass loss of galaxies in groups and clusters with high-resolution DM simulations. We detect weak mass segregation in the inner regions of group/cluster haloes, consistent with observational findings. This applies to samples of galaxy analogues selected using either their present-day mass or past maximum (peak) mass. We find a strong radial trend in the fractional mass lost by the galaxies since peak, independent of their mass. This suggests that segregation is due to massive galaxies having formed closer to the halo centres and not the preferential destruction of smaller galaxies near halo centres. We divide our sample into galaxies that were accreted as a group vs. as a single, distinct halo. We find strong evidence for preprocessing -- the grouped galaxies lose $\sim 35-45\%$ of their peak mass before being accreted onto their final host haloes, compared to single galaxies which lose $\sim12\%$. After accretion, however, the single galaxies lose more mass compared to the grouped ones. These results are consistent with a scenario in which grouped galaxies are preprocessed in smaller haloes while single galaxies `catch up' in terms of total mass loss once they are accreted onto the final host halo. The fractional mass loss is mostly independent of the galaxy mass and host mass, and increases with amount of time spent in a dense environment., Comment: 11 pages, 7 figures, accepted for publication in MNRAS

We present the data release of the Gemini-South GMOS spectroscopy in the fields of 11 galaxy groups at $0.850$ per cent complete for galaxies within the virial radius, and with stellar mass $M_{\rm star}>10^{10.3}M_\odot$. Including galaxies with photometric redshifts we have an effective sample size of $\sim 400$ galaxies within the virial radii of these groups. We present group velocity dispersions, dynamical and stellar masses. Combining with the GCLASS sample of more massive clusters at the same redshift we find the total stellar mass is strongly correlated with the dynamical mass, with $\log{M_{200}}=1.20\left(\log{M_{\rm star}}-12\right)+14.07$. This stellar fraction of $~\sim 1$ per cent is lower than predicted by some halo occupation distribution models, though the weak dependence on halo mass is in good agreement. Most groups have an easily identifiable most massive galaxy (MMG) near the centre of the galaxy distribution, and we present the spectroscopic properties and surface brightness fits to these galaxies. The total stellar mass distribution in the groups, excluding the MMG, compares well with an NFW profile with concentration $4$, for galaxies beyond $\sim 0.2R_{200}$. This is more concentrated than the number density distribution, demonstrating that there is some mass segregation., Accepted for publication in MNRAS. The appendix is omitted due to large figures. The full version will be available from the MNRAS website and from http://quixote.uwaterloo.ca/~mbalogh/papers/GEEC2_data.pdf. Long data tables are available from MNRAS or by contacting the first author

The presence of substructure in galaxy groups and clusters is believed to be a sign of recent galaxy accretion and can be used not only to probe the assembly history of these structures, but also the evolution of their member galaxies. Using the Dressler-Shectman (DS) Test, we study substructure in a sample of intermediate redshift (z ~ 0.4) galaxy groups from the Group Environment and Evolution Collaboration (GEEC) group catalog. We find that 4 of the 15 rich GEEC groups, with an average velocity dispersion of ~525 km s-1, are identified as having significant substructure. The identified regions of localized substructure lie on the group outskirts and in some cases appear to be infalling. In a comparison of galaxy properties for the members of groups with and without substructure, we find that the groups with substructure have a significantly higher fraction of blue and star-forming galaxies and a parent colour distribution that resembles that of the field population rather than the overall group population. In addition, we observe correlations between the detection of substructure and other dynamical measures, such as velocity distributions and velocity dispersion profiles. Based on this analysis, we conclude that some galaxy groups contain significant substructure and that these groups have properties and galaxy populations that differ from groups with no detected substructure. These results indicate that the substructure galaxies, which lie preferentially on the group outskirts and could be infalling, do not exhibit signs of environmental effects, since little or no star-formation quenching is observed in these systems., Comment: 21 pages, 13 figures, MNRAS accepted

We present the global group properties of two samples of galaxy groups containing 39 high quality X-ray selected systems and 38 optically (spectroscopically) selected systems in coincident spatial regions at 0.12, Accepted for publication in the Astrophysical Journal (ApJ). 27 pages, 14 figures, 12 tables

We examine the star formation properties of group and field galaxies in two surveys, the Sloan Digital Sky Survey (SDSS; at z ~ 0.08) and the Group Environment and Evolution Collaboration (GEEC; at z ~ 0.4). Using UV imaging from the GALEX space telescope, along with optical and, for GEEC, near infrared photometry, we compare the observed spectral energy distributions to large suites of stellar population synthesis models. This allows us to accurately determine star formation rates and stellar masses. We find that star forming galaxies of all environments undergo a systematic lowering of their star formation rate between z=0.4 and z=0.08 regardless of mass. Nonetheless, the fraction of passive galaxies is higher in groups than the field at both redshifts. Moreover, the difference between the group and field grows with time and is mass-dependent, in the sense the the difference is larger at low masses. However, the star formation properties of star forming galaxies, as measured by their average specific star formation rates, are consistent within the errors in the group and field environment at fixed redshift. The evolution of passive fraction in groups between z=0.4 and z=0 is consistent with a simple accretion model, in which galaxies are environmentally affected 3 Gyrs after falling into a ~ 10E13 Msun group. This long timescale appears to be inconsistent with the need to transform galaxies quickly enough to ensure that star forming galaxies appear similar in both the group and field, as observed., Comment: 19 pages, MNRAS, in press

The influence of environment in galaxy evolution has been observed in a wide range of environments, where in general red quiescent early-type galaxies preferentially reside in high-density regions. The aim of this thesis is to understand the role that galaxy groups, and in particular group dynamics, play in galaxy evolution. We examine substructure in rich groups at intermediate redshifts and find that 4/15 groups contain substructure, which is preferentially found on the group outskirts. Galaxies in groups with substructure have properties similar to the field, while the galaxies in groups with no substructure are similar to cluster populations. These results indicate that substructure galaxies do not feel the effects of the environment until well inside the group potential. We then study the evolution of group dynamics to z~1 and find that the fraction of non-Gaussian groups increases with redshift, while the fraction of groups with substructure remains constant. Additionally, we find that the quiescent fraction correlates with galaxy stellar mass, but has little or no dependence on group dynamical mass or state. However, we do observe some correlation between substructure and quiescent fraction for low mass galaxies. Finally, we investigate infalling subhalo galaxies to probe the importance of pre-processing in galaxy evolution. At r200 > 2, galaxies in subhaloes show enhanced quenching, when compared to non-subhalo galaxies. At these radii, the infall population dominates, indicating that enhanced quenching is due to the infalling subhalo population. Additionally, the fraction of groups with subhaloes is a function of halo mass, where more massive systems have a higher fraction of subhaloes. We conclude that for groups, pre-processing is insignificant; however, for the most massive clusters a significant fraction (∼ 25%) of the member galaxies have been pre-processed. Doctor of Philosophy (PhD)

Most galaxies in the universe live in galaxy groups, and we can use them to learn a lot about t he influence of environment on galaxy evolution. Historically, galaxy groups have been ident ified by painstakingly obtaining many spectra and finding associated gala-'{ies, however, much larger samples could be found if we had a reliable method of finding groups using photometry. We follow a variation of the Probability Friends of Friends algorithm suggested by Li & Vee (2008) to find galaxy groups in photometric redshift data. Our approach employs a continuous friends-of-friends search in t he t ransverse direction and uses the redshift probability density in redshift space. We use t his method to find galaxy groups in the 4 Canada-France-Hawaii Telescope Legacy Survey Deep Fields, and compare it to a 5th Nearest Neighbor galaxy density search algorithm applied to the same four fields. To fur ther assess our Probability Friends of Friends method, we test it on light cones from the Millennium Simulation. We found that less t han 20% of the Probability Friends of Friends groups with 12 or more members were interlopers. The average density of groups of 12 or more members is ~ 54 per square degree. Our final sample of groups in t he Canada-France-Hawaii Telescope Legacy Survey Deep Fields contains 33 ,279 groups with three or more members, 218 of which have 12 or more members. Master of Science (MS)

Gravitational lensing can be used as a direct probe of the distribution of dark matter around galaxies , groups, and clusters, making it a powerful tool in astrophysics. In this thesis, we introduce the basics of gravitational lensing and weak gravitational lensing. Using weak lensing to study the ensemble-averaged properties of a population of objects, we present a study of galaxy-galaxy lensing of galaxy-sized dark matter halos using data from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Deep. We calculated the average velocity dispersion for an L* galaxy at a redshift of 0.54 to be 113 ± 9 kms-1, with a mass of 1.7 ± 0.3 x 1012 h- 1M⊙. We present the first conclusive evidence for non-spherical galaxy dark matter halos. Our results favour a dark matter halo with an ellipt icity of 0.70 ± 0.18 at > 5σ when averaged over all galaxies. If the sample of foreground lens galaxies is selected by colour , we detect non-spherical halos for all 4 samples except a green subsample. We also consider samples of galaxies divided by colour , redshift and luminosity. Our luminosity samples allowed us to calculate a B-band Tully-Fisher relation which is consistent with theoretical predictions.From our data, we do not detect any evolut ion in galaxy dark matter halos from a redshift of 0. 78 to 0.39, corresponding to no evolut ion from when the Universe was 6.6 Gyr to 9.1 Gyr old in a ACDM cosmology. Master of Science (MS)