Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references. / Also available by subscription via World Wide Web / xvii, 281 leaves, bound ill., charts 29 cm

The physical mechanisms that quench star formation, turning blue star-forming galaxies into red quiescent galaxies, remain unclear. In this Letter, we investigate the role of gas supply in suppressing star formation by studying the molecular gas content of post-starburst galaxies. Leveraging the wide area of the Sloan Digital Sky Survey, we identify a sample of massive intermediate-redshift galaxies that have just ended their primary epoch of star formation. We present Atacama Large Millimeter/submillimeter Array CO(2-1) observations of two of these post-starburst galaxies at z similar to 0.7 with M-* similar to 2 10(11) M-circle dot. Their molecular gas reservoirs of (6.4 +/- 0.8) x 10(9) M-circle dot and (34.0 +/- 1.6) x 10(9) M-circle dot are an order of magnitude larger than comparable-mass galaxies in the local universe. Our observations suggest that quenching does not require the total removal or depletion of molecular gas, as many quenching models suggest. However, further observations are required both to determine if these apparently quiescent objects host highly obscured star formation and to investigate the intrinsic variation in the molecular gas properties of post-starburst galaxies.

When darkmatter haloes are accreted by massive host clusters, strong gravitational tidal forces begin stripping mass from the accreted subhaloes. This stripping eventually removes all mass beyond a subhalo's tidal radius, with unbound mass remaining in the vicinity of the satellite for at most a dynamical time t(dyn). The N-body subhalo study of Chamberlain et al. verified this picture and pointed out a useful observational consequence: correlations between subhaloes beyond the tidal radius are sensitive to the infall time, t(infall), of the subhalo on to its host. We perform this correlation using similar to 160 000 red satellite galaxies in Sloan Digital Sky Survey redMaPPer clusters and find evidence that subhalo correlations do persist well beyond the tidal radius, suggesting that many of the observed satellites fell into their current host less than a dynamical time ago, t(infall) < t(dyn). Combined with estimated dynamical times t(dyn) similar to 3-5 Gyr and SED fitting results for the time at which satellites stopped forming stars, t(quench) similar to 6 Gyr, we infer that for a significant fraction of the satellites, star formation quenched before those satellites entered their current hosts. The result holds for red satellites over a large range of cluster-centric distances 0.1-0.6 Mpc h(-1). We discuss the implications of this result formodels of galaxy formation.

Feedback -- from stars and supermassive black holes -- is the bottleneck of our understanding on galaxy formation: it is likely to be critical, but neither the working mechanism nor the impact is clear. Supernovae (SNe), the dominant feedback force associated with stars, is the subject of this thesis. We use high-resolution, 3D hydrodynamic simulations to study: (i) how a SN blast wave imparts energy to a multiphase ISM; (ii) how multiple SNe regulate a multiphase ISM; (iii) how SNe drive galactic outflows. We focus on better understanding the physics, quantifying the impacts, and testing the simulations against observations.

The majority of typically sized galaxies in the local Universe reside in a common dark matter halo with other similar galaxies known as a galaxy group. However, this was not always the case. Nine billion years ago, when the universe was one third its current age, these galaxies were almost exclusively the only massive galaxy in their dark matter haloes. In this thesis, I use both observational and theoretical methods to attempt to understand the effect these galaxy groups have on the evolution of galaxy properties. I examine the morphological and star formation properties of galaxies in redshift selected samples of galaxy groups at two redshift epochs, z=0 and z=0.4. Galaxy groups contain fewer disk galaxies, as determined by quantitative morphology measures, than similar luminosity field galaxies at both redshift epochs. Furthermore, the difference, at fixed luminosity, grows from 6% at z=0.4 to 19% at z=0. The fraction of passive galaxies, as determined from spectral energy distribution fitting of UV and optical photometry, shows similar behaviour. However, at neither redshift do we find that the disk dominated and star forming galaxies in groups have properties which are significantly different from those in the field. The disks in both environments show similar scaling relations and similar distributions of asymmetry. While both group and field star forming galaxies have similar average star formation rates at fixed stellar mass and redshift. These results argue in favor of a relatively gentle physical mechanism of transformation, like strangulation, which removes the hot halo of a galaxy as it falls into a more massive halo. I use a semi-analytic galaxy formation to understand the accretion histories of galaxies which reside in galaxy groups and clusters at different redshift epochs. The use of a simple model for environmental effects finds that the evolution seen in our observations of passive galaxies can be explained if a galaxy becomes passive 3 Gyrs after falling into a dark matter halo which has a mass of greater than 10E13 Msun. Finally, I use two novel methods for exploring how diffuse stellar mass and dust is distributed in and around galaxy groups. These are important probes of the environmental influence on galaxy evolution. By correlating the positions of hostless type Ia supernovae with galaxy groups, I find that as much as half of a galaxy's stellar mass is in a diffuse form outside of galaxies. These means that processes which shred or harass galaxies must be particularly strong in the group environment. I also find that dust is destroyed by the hot gas contained within groups and clusters. Dust is a necessary component of star formation, and its destruction could be an additional mechanism to suppress the production of stars in galaxy groups.

The majority of typically sized galaxies in the local Universe reside in a common dark matter halo with other similar galaxies known as a galaxy group. However, this was not always the case. Nine billion years ago, when the universe was one third its current age, these galaxies were almost exclusively the only massive galaxy in their dark matter haloes. In this thesis, I use both observational and theoretical methods to attempt to understand the effect these galaxy groups have on the evolution of galaxy properties. I examine the morphological and star formation properties of galaxies in redshift selected samples of galaxy groups at two redshift epochs, z=0 and z=0.4. Galaxy groups contain fewer disk galaxies, as determined by quantitative morphology measures, than similar luminosity field galaxies at both redshift epochs. Furthermore, the difference, at fixed luminosity, grows from 6% at z=0.4 to 19% at z=0. The fraction of passive galaxies, as determined from spectral energy distribution fitting of UV and optical photometry, shows similar behaviour. However, at neither redshift do we find that the disk dominated and star forming galaxies in groups have properties which are significantly different from those in the field. The disks in both environments show similar scaling relations and similar distributions of asymmetry. While both group and field star forming galaxies have similar average star formation rates at fixed stellar mass and redshift. These results argue in favor of a relatively gentle physical mechanism of transformation, like strangulation, which removes the hot halo of a galaxy as it falls into a more massive halo. I use a semi-analytic galaxy formation to understand the accretion histories of galaxies which reside in galaxy groups and clusters at different redshift epochs. The use of a simple model for environmental effects finds that the evolution seen in our observations of passive galaxies can be explained if a galaxy becomes passive 3 Gyrs after falling into a dark matter halo which has a mass of greater than 10E13 Msun. Finally, I use two novel methods for exploring how diffuse stellar mass and dust is distributed in and around galaxy groups. These are important probes of the environmental influence on galaxy evolution. By correlating the positions of hostless type Ia supernovae with galaxy groups, I find that as much as half of a galaxy's stellar mass is in a diffuse form outside of galaxies. These means that processes which shred or harass galaxies must be particularly strong in the group environment. I also find that dust is destroyed by the hot gas contained within groups and clusters. Dust is a necessary component of star formation, and its destruction could be an additional mechanism to suppress the production of stars in galaxy groups.

The luminosity function of galaxies, the measurement of the space density as a function of luminosity, is an important test of cosmology, galaxy formation and evolution. Unfortunately, there is a factor of two variation in recent measurements of the luminosity function. Most of this variation is due to systematic errors, caused by various selection effects. With two large new surveys, the Two degree Field Galaxy Redshift Survey and the Sloan Digital Sky Survey, underway it is important to recognise and eliminate these selection effects if we are going to improve our measurement of the luminosity function and fully utilise these surveys. By measuring the space density of galaxies as a function of surface brightness as well as luminosity, a bivariate brightness distribution, we can comprehend many of the selection effects such as light loss, incompleteness and the visibility of galaxies. Since galaxies have a variety of shapes and sizes, a distribution in luminosity and surface brightness helps to separate out different types of galaxy. Correlations between the luminosity and surface brightness place extra constraints on models of galaxy formation and evolution. When we analyse our results, we find that recent surveys that have not taken into account surface brightness selection effects underestimate the luminosity of the bright end by 5-10%. Using the bivariate brightness distribution, we can constrain the luminosity density to a range that varies by < 20% rather than by a factor of 2. We find that the luminosity function is flat over the range -19.5 < M < -17 and then rises sharply as late-type spiral galaxies begin to dominate. The space density does not vary with surface brightness with the result that low surface brightness galaxies are at least as common as normal galaxies. However, low surface brightness galaxies are also intrinsically faint, following the luminosity-surface brightness correlation for spirals, so they do not contribute significantly to the luminosity density.

Early quiescent galaxies at z similar to 2 are known to be remarkably compact compared to their nearby counterparts. Possible progenitors of these systems include galaxies that are structurally similar, but are still rapidly forming stars. Here, we present Karl G. Jansky Very Large Array (VLA) observations of the CO(1-0) line toward three such compact, star-forming galaxies (SFGs) at z similar to 2.3, significantly detecting one. The VLA observations indicate baryonic gas fractions. greater than or similar to 5 times lower and gas depletion timescales. greater than or similar to 10 times shorter than normal, extended massive SFGs at these redshifts. At their current star formation rates, all three objects will deplete their gas reservoirs within 100 Myr. These objects are among the most gas-poor objects observed at z > 2, and are outliers from standard gas scaling relations, a result that remains true regardless of assumptions about the CO-H-2 conversion factor. Our observations are consistent with the idea that compact, SFGs are in a rapid state of transition to quiescence in tandem with the buildup of the z similar to 2 quenched population. In the detected compact galaxy, we see no evidence of rotation or that the CO-emitting gas is spatially extended relative to the stellar light. This casts doubt on recent suggestions that the gas in these compact galaxies is rotating and significantly extended compared to the stars. Instead, we suggest that, at least for this object, the gas is centrally concentrated, and only traces a small fraction of the total galaxy dynamical mass.

Tidal debris structures are striking evidence of hierarchical assembly -- the premise that the Milky Way and galaxies like it have been built over cosmic time through the coalescence of many smaller objects. In the prevailing Lambda -- Cold Dark Matter cosmology, the vast majority of mergers by number are minor; one dark matter halo, hosting a larger galaxy, dominates the interaction and a smaller object, the satellite, is stripped of mass by tidal forces. When the luminous component of the satellite is disrupted the debris may form structures such as stellar tidal streams or shells, depending on the parameters of the interaction. In this Thesis we examine the properties of this debris left behind by minor mergers theoretically, computationally, and observationally, making strides towards a more complete understanding of what tidal debris can tell us about the history of galaxy formation in the Universe. Around the Milky Way itself we have examined the properties of the Orphan Stream, a stellar tidal stream so named due to uncertainty about the position and current state of its progenitor. Using 3.6 um observations taken as part of the Spitzer Merger History and Shape of the Galactic Halo program, the latest period--luminosity--metallicity relations, and archival data, we compute precise distances to RR Lyrae stream members with state--of--the--art 2.5% relative uncertainties. Fitting an orbit to the data, we measure an enclosed mass for the Milky Way that is in good agreement with other recent results, once the biases in orbit fitting are taken into account. By applying the same technique to N--body simulations we determined that the Orphan progenitor is most likely similar to the classical dwarf spheroidal satellites. We also examined tidal debris more generally, in particular by investigating the source of the morphological dichotomy between shells and streams. We find that the transition from a stream--like to a shell--like morphology occurs when the differential azimuthal precession between the orbits of stars exceeds the position angle subtended by individual petals of the progenitor orbit's rosette. This statement is cast more precisely in terms of scaling relations that control the dispersion of energy and angular momentum in the debris, and we find that the observed morphology can be predicted for a given host, orbit, and mass ratio. This leads us to the idea that the observed occurrence rates of different morphologies can be used to recover, at the population statistics level, the progenitor satellites' orbital infall distribution. This a part of the cosmological accretion history that is otherwise inaccessible. To achieve this in practice requires an unbiased and automated method to detect and classify substructure; we have developed just such a tool and demonstrate its effectiveness. In the upcoming era of LSST and WFIRST the methods and insights developed in this Thesis will be useful in decoding the information about the current state and assembly of galaxies encoded in tidal debris.

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