Environment is known to have a significant impact on the evolution of galaxies. This is most evident in the local Universe, where the oldest and most massive galaxies are found at the of massive galaxy clusters. Current theory predicts that galaxies will form earlier and evolve more rapidly in the densest regions of the Universe. What is not clear is how rapidly the of environment start to have an impact on galaxies, at what stage can we detect physical differences between galaxies in dense regions and those in the field? By the time galaxies are assembled in virialised clusters the effects are clear, but at higher redshift (z ≳ 2), in the unvirialised progenitors of clusters (protoclusters) the effects are harder to detect. In this thesis I study the impact of environment in a z =3.1 protocluster in the SSA22 field. I consider the fraction of mergers in the protocluster, comparing it to the fraction of mergers in field at a similar redshift. My classification is based on the morphology of Lyman break (LBGs), using HST ACS/F814W imaging, which probes the rest frame UV. I find a marginal enhancement of the merger fraction, 48±10 per cent for LBGs in the protocluster compared 30±6 per cent in the field, suggesting that galaxy-galaxy mergers are one of the key driving accelerated star formation and AGN growth in protocluster environments. Having considered the fraction of mergers in the protocluster I then turn my attention to the physical properties of LBGs. I use multiwavelength data and spectral energy distribution fitting to determine the mass of LBGs in the protocluster and in the field. I find no statistical evidence for an enhancement of mass in the protocluster, suggesting that the protocluster environment has not impacted the average mass of LBGs at this redshift. It is possible that the protocluster LBG population may become more massive than LBGs in the field at lower redshift, or the galaxies may cease to be detectable by the Lyman break method before a mass difference between the protocluster galaxies and field is observable. Finally I consider the Lyman-α blobs (LABs) within the protocluster. These are large (~10- 100kpc) scale regions of diffuse Lyman-α emission, thought to be associated with overdense regions. 35 LABs have been detected in the SSA22 protocluster, indicating the presence of large clouds of gas in the circumgalactic medium. A debate has arisen regarding the powering mechanism of the LABs, particularly between star forming processes (e.g. Lyman-α escaping from a star forming galaxy or photoionizing radiation escaping from a star forming galaxy or active galactic nuclei) and a cold accretion model. The latter involves gas gravitationally cooling as it falls into the centre of a dark matter halo to feed a central galaxy. Some of this energy heats the cold gas, which then emits Lyman-α as it cools. The cold gas accretion theory gained popularity because some LABs appear not to contain a luminous galaxy or AGN which could explain the observed emission. One suggestion is that the central galaxy could be hidden by dust and that this could explain the lack of a detection in UV or optical. I therefore use SCUBA2 850μm imaging to search for submm sources (dusty star forming galaxies) in the LABs. I detect submm sources in only two of the LABs at 3.5δ, however, stacking all the LABs gives an average flux density of S850 = 0.6±0.2mJy. This suggests that on average the LABs do contain a submm source which could be a dusty galaxy. However, stacking the LABs by size indicates that only the largest third (area ≳ 1800kpc²) have a mean detection, at 4.5δ, with S850 = 1.4±0.3mJy, suggesting that different mechanisms may dominate the larger and smaller LAB populations. I explore two possible mechanisms for powering the LABs, cold accretion and central star forming galaxies. I find that central star formation is more likely to be the dominant source of emission, with cold accretion playing a secondary role.

In this thesis, I develop and combine strong lensing and dynamical probes of the mass of early-type galaxies (ETGs) in order to improve our understanding of their dark and luminous mass structure and evolution. Firstly, I demonstrate that the dark matter halo of our nearest brightest cluster galaxy (BCG), M87, is centrally cored relative to the predictions of dark-matter-only models, and suggest an interpretation of this result in terms of dynamical heating due to the infall of satellite galaxies. Conversely, I find that the haloes of a sample of 12 field ETGs are strongly cusped, consistent with adiabatic contraction models due to the initial infall of gas. I suggest an explanation for these differences in which the increased rate of merging and accretion experienced by ETGs in dense environments leads to increased amounts of halo heating and expansion, such that the signature of the halo's initial contraction is erased in BCGs but retained in more isolated systems. Secondly, I find evidence that the stellar-mass-to-light ratio declines with increasing radius in both field and cluster ETGs. With M87, I show that the strength of this gradient cannot be explained by trends in stellar metallicity or age if the stellar initial mass function (IMF) is spatially uniform, but that an IMF which becomes increasing bottom-heavy towards the galaxy centre can fully reproduce the inference on the stellar mass. Finally, I use the sizes, stellar masses and luminous structures of two samples of massive ETGs at redshift z ~ 0.6 to set constraints on the mechanisms of ETG growth. I find that ETGs in dense cluster environments already lie on the local size-mass relation at this redshift, contrary to their isolated counterparts, and suggest that this may be evidence for their accelerated growth at early times due to the higher incidence of merger events in clusters. I also show that massive compact ETGs at this redshift are composed of a compact, red, spheroidal core surrounded by a more extended, diffuse, bluer envelope, which may be a structural imprint of their ongoing inside-out growth. Overall, the studies presented in this thesis suggest a coherent scenario for ETG evolution which is dominated by hierarchical processes.

We conduct a deep mid-infrared census of nine massive galaxy clusters at (0 < z < 1.3) with a total of ~ 1500 spectroscopically confirmed member galaxies using Spitzer /IRAC photometry and established mid-infrared color selection techniques. Of the 949 cluster galaxies that are detected in at least three of the four IRAC channels at the >= 3 sigma level, we identify 12 that host mid-infrared selected active galactic nuclei (IR-AGN). To compare the IR-AGN across our redshift range, we define two complete samples of cluster galaxies: (1) optically-selected members with rest-frame VAB magnitude < -21.5 and (2) mid-IR selected members brighter than (M*_3.6 +0.5), i.e. essentially a stellar mass cut. In both samples, we measure f_IR-AGN ~ 1% with a strong upper limit of ~3% at z < 1. This uniformly low IR-AGN fraction at z < 1 is surprising given the fraction of 24 micrometer sources in the same galaxy clusters is observed to increase by about a factor of four from z ~ 0 to z ~ 1; this indicates that most of the detected 24 micrometer flux is due to star formation. Only in our single galaxy cluster at z = 1.24 is the IR-AGN fraction measurably higher at ~15% (all members; ~70% for late-types only). In agreement with recent studies, we find the cluster IR-AGN are predominantly hosted by late-type galaxies with blue optical colors, i.e. members with recent/ongoing star formation. The four brightest IR-AGN are also X-ray sources; these IR+X-ray AGN all lie outside the cluster core (R_proj > 0.5 Mpc) and are hosted by highly morphologically disturbed members. Although our sample is limited, our results suggest that f_IR-AGN in massive galaxy clusters is not strongly correlated with star formation at z < 1, and that IR-AGN have a more prominent role at z &gt; 1.

It has become clear that the global star formation rate in the Universe has been decreasing since at least z~1, and blue, star-forming galaxies are transformed into red, passive galaxies through one or more processes. The origin of this decline and transformation remains unclear. The role environment plays in all this is especially uncertain. Despite the observed domination of a passive population in the cores of clusters, in contrast to the more actively star-forming field population, whether or not, and how environment affects the properties of galaxies when they fall into clusters is an unsettled question. In this thesis, we look into these issues by examining both the passive and star-forming galaxies, from the cores out to the infall regions, in a large sample of clusters at 0.15<z<0.36 we detected from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We find that in the cores of clusters, the red-sequence galaxies are a mixture of two populations, indicated by the inflexion in their luminosity function. There is no strong evolution in the shape of the red-sequence between z~0.4 and z~0.2; however, from z~0.2 to today, there is a rapid increase in the number of faint galaxies on the red-sequence relative to the bright ones, suggesting a rapid quenching of the faint galaxies in cluster cores within the last few billion years. At z~0.2, we find that the red fraction (star-forming fraction), at all stellar mass explored (9.0<log10(M*/M_solar)<11.5), shows no dependence on the distance from cluster centres, in the range 3<r<7Mpc; but within the inner 3 Mpc, we see a clear increase (decrease) in the red fraction (star-forming fraction). Also, for the lowest stellar mass galaxies, their red fraction has increased by a factor of 2 from z~0.3 to z~0.2 (over 1 Gyr), and yet we do not detect any difference between the star formation properties of the star-forming galaxies in clusters at all radii and that in the field. This suggests that for the low mass galaxies, it is likely that a mechanism that truncates star formation rapidly (within 1 Gyr) is at work. In the outskirts of the clusters, despite the low density contrast with the field, the red fraction is still higher than that in the field, suggesting that those galaxies have had their star formation quenched relative to the field population, supporting the pre-processing scenario.

In this thesis I investigate the hosts and cluster environments of a sample of 41 radio galaxies between z = 0.4 and z = 0.6. I use spectroscopic data for a 24 object subsample to investigate their star formation histories via the strength of the 4000A break. I find that the higher radio luminosity or high excitation objects in the sample have evidence for young stellar populations, but the lower radio luminosity or low excitation objects do not. My investigations into the Fundamental Plane (FP) of 18 of the radio galaxies, using the same spectroscopic data as well as data from the literature, show that the Fanaroff- Riley type I objects (FRIs) lie on the FP of local radio galaxies once corrected for passive evolution but the Fanaroff-Riley type II objects (FRIIs) do not. I suggest that an evolution in the size of the host galaxies, aided by a combination of passive evolution and a mass-dependent evolution in the mass-to-light ratios, may explain the observed offsets. Finally, I use wide field multi-band imaging to investigate the cluster environments of the full z ~ 0.5 sample. I find that the environmental overdensity is positively correlated with the radio luminosity and observe a greater number of close companions around the FRIIs than the FRIs (albeit with only nine FRIs in the sample). The cluster environments of the radio galaxies with the greatest host luminosities show tentative evidence for an alignment between the major axis of a galaxy and that of its cluster, whilst there are hints that the objects with the highest radio luminosities have clusters whose major axis is aligned with the position angle of the radio jet. My results suggest a picture in which FRII type radio sources reside in particularly rich cluster environments at z ~ 0.5 but FRI type radio sources in less rich environments. The environment plays a key role in determining both the radio properties of the galaxy and the evolution of its host. The effect of the environment on the emission line properties and star formation histories of the galaxies leads to the overlap seen in the morphological and spectral properties of radio galaxies.

It has become clear that the global star formation rate in the Universe has been decreasing since at least z~1, and blue, star-forming galaxies are transformed into red, passive galaxies through one or more processes. The origin of this decline and transformation remains unclear. The role environment plays in all this is especially uncertain. Despite the observed domination of a passive population in the cores of clusters, in contrast to the more actively star-forming field population, whether or not, and how environment affects the properties of galaxies when they fall into clusters is an unsettled question. In this thesis, we look into these issues by examining both the passive and star-forming galaxies, from the cores out to the infall regions, in a large sample of clusters at 0.15<z<0.36 we detected from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We find that in the cores of clusters, the red-sequence galaxies are a mixture of two populations, indicated by the inflexion in their luminosity function. There is no strong evolution in the shape of the red-sequence between z~0.4 and z~0.2; however, from z~0.2 to today, there is a rapid increase in the number of faint galaxies on the red-sequence relative to the bright ones, suggesting a rapid quenching of the faint galaxies in cluster cores within the last few billion years. At z~0.2, we find that the red fraction (star-forming fraction), at all stellar mass explored (9.0<log10(M*/M_solar)<11.5), shows no dependence on the distance from cluster centres, in the range 3<r<7Mpc; but within the inner 3 Mpc, we see a clear increase (decrease) in the red fraction (star-forming fraction). Also, for the lowest stellar mass galaxies, their red fraction has increased by a factor of 2 from z~0.3 to z~0.2 (over 1 Gyr), and yet we do not detect any difference between the star formation properties of the star-forming galaxies in clusters at all radii and that in the field. This suggests that for the low mass galaxies, it is likely that a mechanism that truncates star formation rapidly (within 1 Gyr) is at work. In the outskirts of the clusters, despite the low density contrast with the field, the red fraction is still higher than that in the field, suggesting that those galaxies have had their star formation quenched relative to the field population, supporting the pre-processing scenario.

We use Bayesian statistics and Markov chain Monte Carlo (MCMC) techniques to construct dynamical models for the spiral galaxy NGC 6503. The constraints include surface brightness profiles which display a Freeman Type II structure; HI and ionized gas rotation curves; the stellar rotation, which is nearly coincident with the ionized gas curve; and the line of sight stellar dispersion, which displays a $\sigma-$drop at the centre. The galaxy models consist of a S\'rsic bulge, an exponential disc with an optional inner truncation and a cosmologically motivated dark halo. The Bayesian/MCMC technique yields the joint posterior probability distribution function for the input parameters, allowing constraints on model parameters such as the halo cusp strength, structural parameters for the disc and bulge, and mass-to-light ratios. We examine several interpretations of the data: the Type II surface brightness profile may be due to dust extinction, to an inner truncated disc or to a ring of bright stars; and we test separate fits to the gas and stellar rotation curves to determine if the gas traces the gravitational potential. We test each of these scenarios for bar stability, ruling out dust extinction. We also find that the gas cannot trace the gravitational potential, as the asymmetric drift is then too large to reproduce the stellar rotation. The disc is well fit by an inner-truncated profile, but the possibility of ring formation by a bar to reproduce the Type II profile is also a realistic model. We further find that the halo must have a cuspy profile with $\gamma \gtrsim 1$; the bulge has a lower $M/L$ than the disc, suggesting a star forming component in the centre of the galaxy; and the bulge, as expected for this late type galaxy, has a low S\'{e}rsic index with $n_b\sim1-2$, suggesting a formation history dominated by secular evolution. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2010-01-10 00:11:41.946

We perform spectral energy distribution fitting to the total integrated light, bulge and disk components of ≈ 650,000 spectroscopically selected galaxies from the sloan digital sky survey data release 7. Using 4-band photometry (u, g, r, i) we derive physical properties for these components with particular emphasis placed on the star formation rates (SFR) and stellar masses. Using the total integrated fits as an indicator of the goodness of fit, we show that reliable estimates of the SFR can be recovered using a specific SFR (sSFR) cut of log(sSFR /yr) ≥ −10.45. We construct a close pairs sample and match isolated controls based on stellar mass, z and local density for galaxies that pass the sSFR cut. We develop a method to cross correlate the pair galaxies’ star formation rate posterior probability distribution functions (SFR PDFs) with the control SFR PDFs as a function of the pair galaxies projected separation, rp. We show that the SFR of the close pair galaxies is enhanced relative to the control sample. The SFR enhancement is at a level of ≈ 0.25 dex above that of the control at the closest separations and declines to a plateau at ≈ 0.15 dex for separations of 30 < rp < 60 kpc/h. Between 60 < rp < 80 kpc/h there appears to be a slight increase in the enhancement to a level ≈ 0.25 dex above the control. It is suggested that we observe this increase, where other studies have failed to, based on the updated photometry provided by Simard et al. (2011). From our total pair sample we also select a subsample of galaxies that are classified as active galactic nuclei (AGN). We note that at close separations the pair AGN galaxies have enhanced SFRs relative to their matched controls. The SFR enhancement is largest at the smallest separations, reaching a level of ≈ 0.3 dex above the control. The SFR enhancement for the AGN pairs becomes consistent with their controls at projected separations of 20 < rp < 80 kpc/h. We construct a bulge and disk pair sample that are required to pass the sSFR cut and match control bulges and disks, respectively, that also pass the sSFR cut. We cross correlate the bulge and disk pairs with their respective controls. We measure significant SFR enhancement in the bulge component of the interacting pairs. The SFR enhancement is highest at small separations, ≈ 0.4 dex, and steadily declines to ≈ 0.1 dex before turning around beyond rp > 50 kpc/h to again reach a level ≈ 0.4 dex above the control bulges. The disk SFR enhancement is relatively flat beyond rp > 30 kpc/h to a level ≈ 0.1 dex above the control and largely consistent with the control at close separations. The bulge and disk results suggest that the majority of induced star formation during an interaction is occurring in the bulge component, but that there is still slight SFR enhancement in the disk. We suggest that the upturn in the total and bulge SFR enhancement could potentially be caused by a delay between the interaction of the galaxy pairs and the onset of induced star formation. / Graduate

abstract: New measurements of the Hα luminosity function (LF) and star formation rate (SFR) volume density are presented for galaxies at z∼0.62 in the COSMOS field. These results are part of the Deep And Wide Narrowband Survey (DAWN), a unique infrared imaging program with large areal coverage (∼1.1 deg 2 over 5 fields) and sensitivity (9.9 × 10 −18 erg/cm 2 /s at 5σ). The present sample, based on a single DAWN field, contains 116 Hα emission- line candidates at z∼0.62, 25% of which have spectroscopic confirmations. These candidates have been selected through comparison of narrow and broad-band images in the infrared and through matching with existing catalogs in the COSMOS field. The dust-corrected LF is well described by a Schechter function with L* = 10 42.64±0.92 erg s −1 , Φ* = 10 −3.32±0.93 Mpc −3 (L* Φ* = 10 39.40±0.15 ), and α = −1.75 ± 0.09. From this LF, a SFR density of ρ SF R =10 −1.37±0.08 M○ yr −1 Mpc −3 was calculated. An additional cosmic variance uncertainty of ∼ 20% is also expected. Both the faint end slope and luminosity density that are derived are consistent with prior results at similar redshifts, with reduced uncertainties. An analysis of these Hα emitters’ sizes is also presented, showing a direct corre- lation between the galaxies’ sizes and their Hα emission. / Dissertation/Thesis / Masters Thesis Astrophysics 2017

When we look throughout the Universe, we can see the stages of galaxy evolution across cosmic time; however there are still many unanswered questions about the details of galaxy evolution. How did galaxies like our Milky Way assemble? Do the first galaxies look different than our own? What makes galaxies stop forming stars? Many of these questions can be addressed by studying the detailed chemistry of gas located in and around galaxies. Absorption lines imprinted on quasar spectra probe this hard-to-see gas within and surrounding galaxies, giving an luminosity-unbiased census of gas from z~0 to the epoch of the most distant quasars. In this thesis, I present two samples of high resolution spectra of quasars obtained from both ground- and space-based observatories to study the evolution of galaxies through their gas-phase absorption lines. The first of the two samples presented in this thesis consists of the 100 quasar sightlines from the XQ-100 legacy survey completed with the X-Shooter spectrograph on the Very Large Telescope in Chile. The XQ-100 survey provides a blind sample of over 350 HI absorption line systems associated with galaxies with column densities 18.8<=logN(HI)<=21.5. Using this sample, I investigated the evolution of neutral gas reservoirs from z~4.5 to z~2.0. I demonstrate that the lower column density sub-damped Lyman alpha systems (with column densities 19.0<=logN(HI)<20.3) contribute ~20% of the HI observed in galaxy gas reservoirs compared to the rarer but high column density damped Lyman alpha systems (DLAs; logN(HI)>=20.3). Furthermore, I show that using the presence of metal lines (particularly MgII absorption) to identify and select absorbing systems can potentially bias the properties of the sample; absorbers selected to contain strong metal line absorbers tend to exclude low metallicity and low HI column density systems. I demonstrate that the systems missed by metal-selected searches can have a significant impact on the study of the cosmic evolution of neutral gas reservoirs. In addition to the HI content, the metal abundances for 13 elements in the 41 DLAs of the XQ-100 sample are presented. In concert with my literature compilation of 280 DLA metal abundance measurements, I studied the dust-corrected [Zn/Fe]. This work emphasizes that near-IR coverage of X-Shooter provides unprecedented access to MgII, CaII and TiII lines (at redshifts 3-4) to provide additional evidence for subsolar [Zn/Fe] ratio in DLAs, a chemical signature that DLAs can be high-redshift dwarf galaxy analogues. Furthermore, the XQ-100 DLA sample consists of several unique systems that probe the effects of environment on the chemical evolution of the Universe, as well as the chemical makeup of the first generations of stars. I demonstrate that DLAs close to their background quasar (within 5000 km/s) with logN(HI)<21.0 show lower [S/H] and [Fe/H] (relative to intervening systems with similar redshift and N(HI)), whilst higher [S/H] and [Si/H] are seen in these proximate systems with logN(HI)>21.0. Contrary to previous studies, DLAs within 10,000 km/s of another DLA show no difference in [alpha/Fe] relative to single DLAs matched in metallicity and redshift. In addition, I present follow-up high-resolution data of J0034+1639, a sightline containing three DLAs, including a metal-poor DLA with [Fe/H]=-2.82 (the third lowest [Fe/H] in DLAs identified to date) at z=4.25. In the latter part of this thesis, I study the circumgalactic medium (CGM) of galaxies that host an active galactic nucleus (AGN). AGN are thought to play a critical role in shaping galaxies, but their effect on the gaseous reservoirs surrounding galaxies is not well studied. I present results from the COS-AGN survey: 19 quasar sightlines that probe the gas surrounding 20 optically-selected AGN host galaxies observed over 65 hours with the Hubble Space Telescope. Absorption lines from a variety of species are measured and compared to a stellar mass and impact parameter matched sample of sightlines through non-AGN galaxies. Amongst the observed species in the COS-AGN sample (HI, CII, SiII, SiIII, CIV, SiIV, NV), only HI shows a high covering fraction whilst many of the metal ions are not detected in individual sightlines. A sightline-by-sightline comparison between COS-AGN and the control sample yields no significant difference in equivalent width distribution. However, stacked spectra of the COS-AGN and control samples show significant enhancements in the equivalent width of both Lya and SiIII at high impact parameters (>164 kpc) by a factor of +0.45+/-0.05 dex and >+0.75 dex respectively. The lack of detections of both high-ionization species near the AGN and strong kinematic offsets between the absorption systemic galaxy redshifts indicates that neither the AGN's ionization nor its outflows are the origin of these differences. Instead, I suggest the observed differences could result from either AGN hosts residing in haloes with intrinsically distinct gas properties, or that their CGM has been affected by a previous event, such as a starburst, which may also have fuelled the nuclear activity. / Graduate