Lenticular and elliptical galaxies, collectively referred to as "early-type galaxies" (ETGs), are commonly thought to represent the end-points of galaxy evolution. Lying in the red sequence of galaxies, these objects are defined by their mostly old stellar populations and by their "red and dead" appearance in optical observations. Much progress in understanding these objects has been made with integral-field spectroscopy in recent years, with results repeatedly pointing to a link between early-type galaxies and high-redshift spiral galaxies. However, the exact nature of this link remains unclear, with a wide variety of evolution scenarios likely required to fully explain the range of observed early-type galaxy properties. In my study, I analysed observations of twelve early-type galaxies taken with the Mitchell Integral-Field Spectrograph at McDonald Observatory, Texas. These galaxies have previously been found to contain detectable quantities of neutral hydrogen gas, with ten out of the twelve displaying large-scale hydrogen disks. I extracted line-of-sight kinematics of the stellar and ionised gas components of these galaxies, and I used various modelling approaches to constrain their stellar population parameters as well as their three-dimensional mass structure in terms of both dark and visible components. An important feature of this study is the wide field of view of the spectroscopic observations, which reach beyond two half-light radii for almost all of the sample; this remains rare for integral-field unit (IFU) studies of ETGs, and so sets this study apart from most earlier works. The gas-rich nature of the sample is likewise novel. I find all aspects of my analysis to yield a consistent view of these galaxies' evolution, in which one or more gaseous interaction events served to shape them into their observed forms. I find these galaxies to contain low dark matter fractions on average within the inner half-light radius, and I also find mass modelling to favour near-isothermal total density profiles over much of the sample.

The abundance of molecular hydrogen (H2), the primary coolant in primordial gas, is critical for the thermodynamic evolution and star–formation histories in early protogalaxies. Suppression of H2–cooling in early protogalaxies can occur via photodissociation of H2 (by ultraviolet Lyman–Werner [LW] photons) or by photodetachment of H−, a precursor in H2 formation (by infrared [IR] photons). It is widely believed that the formation of the first massive black hole “seeds,” with masses 104−6 M⊙, in primordial halos may be enabled if H2–cooling is suppressed. We study the radiative feedback processes that suppress H2–cooling in primordial proto- galaxies. Previous studies have typically adopted idealized spectra, with a blackbody or a power–law shape, in modeling the chemistry of metal–free protogalaxies, and utilized a single parameter, the critical UV flux, or Jcrit, to determine whether H2–cooling is prevented. This can be misleading, as independent of the spectral shape, there is a a critical curve in the (kLW,kH−) plane, where kLW and kH− are the H2–dissociation rates by LW and IR photons, which determines whether a protogalaxy can cool below ∼ 1000 Kelvin. In Chapter 1, we use a one–zone model to follow the chemical and thermal evolution of gravitationally collapsing protogalactic gas, to compute this critical curve, and provide an accurate analytical fit for it. We improve on previous works by considering a variety of more realistic Pop III or Pop II-type spectra from population synthesis models and perform fully frequency–dependent calculations of the H2–photodissociation rates for each spectrum. We compute the ratio kLW/kH− for each spectrum, as well as the minimum stellar mass M∗, for various IMFs and metallicities, required to prevent cooling in a neighboring halo a distance d away. We provide critical M∗/d2 values for suppression of H2–cooling, with analytic fits, which can be used in future studies. Determining the photodissociation rate of H2 by an incident LW flux is crucial, but prohibitively expensive to calculate on the fly in simulations. The rate is sensitive to the H2 rovibrational distribution, which in turn depends on the gas density, temperature, and incident LW radiation field. In Chapter 2, we use the publicly available cloudy package to model primordial gas clouds and compare exact photodissociation rate calculations to commonly–used fitting formulae. We find the fit from Wolcott-Green et al. (2011) is most accurate for moderate densities n ∼ 103cm−3 and temperatures, T ∼ 103K, and we provide a new fit, which captures the increase in the rate at higher densities and temperatures, owing to the increased excited rovibrational populations in this regime. Our new fit has typical errors of a few percent percent up to n ≤ 107 cm−3, T ≤ 8000K, and H2 column density NH2 ≤ 1017 cm−2, and can be easily utilized in simulations. We also show that pumping of the excited rovibrational states of H2 by a strong LW flux further modifies the level populations when the gas density is low, and noticeably decreases self-shielding for J21 > 103 and n < 102cm−3. This may lower the “critical flux” at which primordial gas remains H2–poor in some protogalaxies, enabling massive black hole seed formation. In Chapter 3, we study the thermal evolution of UV–irradiated atomic cooling halos using high–resolution three–dimensional hydrodynamic simulations. We consider the effect of H− photodetachment by Lyα cooling radiation in the optically–thick cores of three such halos, a process which has not been included in previous simulations. H− is a precursor of molecular hydrogen, and therefore, its destruction can diminish the H2 abundance and cooling. We find that the critical UV flux for suppressing H2–cooling is decreased by up to a factor of a few when H− photodetachment by Lyα is included. In a more conservative estimate of the trapped Lyα energy density, we find the critical flux is decreased by ∼ 15 − 50 per cent. Our results suggest that Lyα radiation may have an important effect on the thermal evolution of UV–irradiated halos, and therefore on the potential for massive black hole formation.

The work presented in this thesis investigates the evolution of starforming galaxies over the last ten billion years. This time period encompasses nearly three-fourths of the age of the Universe, when a substantial fraction of the total stellar mass forms, and the sites of active star formation shift to lower-mass galaxies. The first study presented here combines galaxies from the spectroscopic datasets of the FORS Deep Field and the MUNICS Survey and provides the first significant investigation of the specific star formation rate (SSFR; star formation rate [SFR] per unit stellar mass) over a wide range of stellar masses and redshifts (reaching redshift z = 1:5). From [OII]-derived SFRs, we find that low-mass galaxies have higher SSFRs all the way to z = 1:5, implying that star formation contributes progressively more to the growth of stellar mass in low-mass galaxies than in high-mass galaxies. In the follow-up to this study, we combine several near-infrared-selected samples to create one of the largest collections of galaxies with spectroscopic redshifts and morphologies from Hubble Space Telescope images, to characterize the stellar mass build up in galaxies since z = 1:6. The primary data comes from the FORS Deep Field, the MUNICS Survey, the GOODS-South field as observed by the K20 survey and ESO, and the Sloan Digital Sky Survey as a local comparison sample. After bringing together extensive photometric and spectroscopic data sets from several publicly available surveys, we use identical methods to derive physical properties and investigate how galaxy populations evolve with time. Galaxy properties include stellar masses derived from multiwavelength photometry, star formation rates calculated from [OII][lambda]3726Å emission lines, metallicity, color, and SSFRs. We find that the reddest, yet actively star-forming, disk-dominated galaxy population present at z ~ 1:3, decreases in number by z ~ 0:3 during the same timeframe when the bluest quiescent, disk-dominated galaxy population increases in number. We confirm the previously identified morphological separation in the SSFR versus M[subscript asterisk] plane found for local samples and for galaxies at z = 0:7: bulge-dominated galaxies are more massive and have lower SSFRs. We extend this relation for the first time to z = 1:6, showing that galaxies with high SSFRs and diskdominated structures tend to shift to lower masses as redshift decreases. We identify an observed upper envelop in SSFR that lies roughly parallel to lines of constant SFR, decreases with time, and is unaffected by incompleteness among the samples. We apply common star formation histories (constant, ex ponential, and power law) to understand the evolving populations we see, but cannot simultaneously reproduce low-mass galaxies with high SSFRs and highmass galaxies with low SSFRs at all redshifts and over our full mass range. Current semi-analytic models attempt to understand the mass at which galaxies stop forming stars through connections to Active Galactic Nuclei feedback, gas consumption, declining galaxy merger rates and/or changes in the incoming cold gas supply, but none can explain the gradual and constant decline of star formation consistent among all galaxies below this mass. We suggest a possible resolution where star formation histories of galaxies are dependent on morphology, in addition to the growing evidence for lower mass galaxies to begin forming stars at later times, and with lower initial SFRs than the initial SFRs experienced at earlier times by higher mass galaxies. / text

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) will map the power spectrum of 0.8 million blindly discovered Lyman-alpha Emitting Galaxies (LAE) using a revolutionary new array of massively replicated, fiber-fed spectrographs dubbed the Visible Integral-Field Replicable Unit Spectrograph (VIRUS). In the era of the Hobby-Eberly Telescope wide-field upgrade, the current Low Resolution Spectrograph (LRS) must be replaced with a fiber instrument. In this thesis, I discuss the development of the second generation LRS (LRS2), which is an R>1200 multi-channel instrument based on the VIRUS design and fed by a 287 fiber, 7” x 12” microlens coupled integral field unit. I focus on the blue optimized version of the instrument (3720<[lamda] (Angstroms)<7000), specifically on the opto-mechanical design of the VPH grisms. With the purpose of making the instrument ideal for the follow-up of LAE in the HETDEX survey, I discuss the science drivers for selecting the spectral resolution of the instrument. To test the utility of such an instrument, I present R~2400 spectra of two LAE that were originally discovered in the HETDEX Pilot Survey (Adams et al. 2011). These data were taken with the VIRUS prototype spectrograph in a high-resolution mode at the McDonald Observatory Harlan J. Smith 2.7 m telescope. The Lyman-alpha line profiles are constrained by near-infrared observations of rest-frame optical emission lines from Finkelstein et al. (2011), which set the systemic redshift of the galaxies. I discuss the velocity offsets of the Lyman-alpha line from the systemic line center and the implications for the HETDEX survey. I compare the line profiles to theory, specifically to those describing dust attenuation, outflows or inflows of neutral gas on the galactic scale, and attenuation in the intergalactic medium. This study provides an example of how LRS2 can be used to probe Lyman-alpha emission in 2<z<3 star-forming galaxies. / text

Stellar bars are the most important internal drivers of the evolution of disk galaxies because they efficiently redistribute mass and angular momentum in the baryonic and dark matter components of galaxies. Mounting evidence suggests that mechanisms other than major mergers of galaxies, such as minor mergers, gas accretion, and bar-driven secular processes, play an important role in galaxy evolution since a redshift z~2. In order to characterize the evolution of barred disks, this thesis presents one of the most comprehensive studies of barred galaxies in the field at low redshifts, and also as a function of environment across galaxy clusters of different densities. This work improves significantly on earlier studies by using quantitative methods to characterize bars, analyzing high-quality data from some of the largest disk galaxy samples to date, and using results across a range of Hubble types and environments to test different theoretical models for the evolution of disk galaxies. Our main results are summarized below: (1) Studies done as a part of this thesis have quantitatively shown for the first time that the optical bar fraction in z~ 0 field galaxies is a sensitive and non-monotonic function of host galaxy properties, such as the luminosity, stellar mass, and bulge-to-disk ratio. We find that at z~0, the bar fraction increases significantly from galaxies of intermediate mass and Hubble types (Sb) toward those of lower mass and late Hubble types (Sd-Sm). The behavior from intermediate to early Hubble types is more uncertain. These results, which have been subsequently confirmed by independent studies, set constraints for theoretical models and in particular underline the importance for bar growth of angular momentum exchange between the bar, disk, bulge, and dark matter halo, as well as the possible triggering of bars by external satellites and interactions with the dark matter. Furthermore, our results at optical and near-infrared wavelengths on the fraction and sizes of bars at z~0 provide the zero-redshift anchor point for studies of bars at higher redshifts with current and future space missions (e.g., ACS, WFC3, JWST), and allow us to assess the systematic effects in such studies. (2) Although cluster environments are unique laboratories for investigating the evolution of barred disks, only sparse and disparate results have emerged from early studies. In this thesis, we study barred disks in clusters using high-quality data from the Hubble Space Telescope Advanced Camera for Surveys for the moderately-rich cluster Abell 901/902 (characterized by a galaxy number density n~1,000 gal Mpc⁻³) at z~0.165, and of the Coma cluster at z~0.02, the densest cluster (n~10,000 gal Mpc⁻³) in the nearby Universe. We find that the optical bar fraction for bright, early Hubble type disk galaxies does not show a statistically significant variation (within the error bars of ± 10 to 12%) as a function of galaxy environment within the Abell 901/902 cluster, as well as between the Abell 901/902 cluster and the field. Similarly, the optical bar fraction for bright S0 galaxies shows no statistically significant variation (within the error bars of ±10%) between the Virgo, Abell 901/902, and core of the Coma clusters, even though these environments span over an order of magnitude in galaxy number density (n~300 to 10,000 gal Mpc⁻³). We suggest that the S0 bar fraction is not greatly enhanced in denser environments, such as the core of Coma, due to the predominance of high speed encounters over slow ones, the tidal heating of S0 disks, and the low gas content of S0s in rich clusters. / text

Mode of access: World Wide Web. / Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 180-192). / Electronic reproduction. / Also available by subscription via World Wide Web / xviii, 192 leaves, bound col. ill. 29 cm

We use the deep CANDELS observations in the GOODS North and South fields to revisit the correlations between stellar mass (M-*), star formation rate (SFR) and morphology, and to introduce a fourth dimension, the mass-weighted stellar age, in galaxies at 1.2 < z < 4. We do this by making new measures of M-*, SFR, and stellar age thanks to an improved SED fitting procedure that allows various star formation history for each galaxy. Like others, we find that the slope of the main sequence (MS) of star formation in the (M-*; SFR) plane bends at high mass. We observe clear morphological differences among galaxies across the MS, which also correlate with stellar age. At all redshifts, galaxies that are quenching or quenched, and thus old, have high Sigma(1) (the projected density within the central 1 kpc), while younger, star-forming galaxies span a much broader range of Sigma(1), which includes the high values observed for quenched galaxies, but also extends to much lower values. As galaxies age and quench, the stellar age and the dispersion of Sigma(1) for fixed values of M* shows two different regimes: one at the low-mass end, where quenching might be driven by causes external to the galaxies; the other at the high-mass end, where quenching is driven by internal causes, very likely the mass given the low scatter of Sigma(1) (mass quenching). We suggest that the monotonic increase of central density as galaxies grow is one manifestation of a more general phenomenon of structural transformation that galaxies undergo as they evolve.

We revisit the proposed extended Schmidt law, which posits that the star formation efficiency in galaxies depends on the stellar mass surface density, by investigating spatially resolved star formation rates (SFRs), gas masses, and stellar masses of star formation regions in a vast range of galactic environments, from the outer disks of dwarf galaxies, to spiral disks and to merging galaxies, as well as individual molecular clouds in M33. We find that these regions are distributed in a tight power law as Sigma(SFR) proportional to (Sigma(0.5)(star)Sigma(gas))(1.09), which is also valid for the integrated measurements of disk and merging galaxies at high-z. Interestingly, we show that star formation regions in the outer disks of dwarf galaxies with Sigma(SFR) down to 10(-5) M(circle dot)yr(-1) kpc(-2), which are outliers of both the Kennicutt-Schmidt and Silk-Elmegreen laws, also follow the extended Schmidt law. Other outliers in the Kennicutt-Schmidt law, such as extremely metal-poor star formation regions, also show significantly reduced deviation from the extended Schmidt law. These results suggest an important role for existing stars in helping to regulate star formation through the effect of their gravity on the midplane pressure in a wide range of galactic environments.

This paper provides an update of our previous scaling relations between galaxy-integrated molecular gas masses, stellar masses, and star formation rates (SFRs), in the framework of the star formation main sequence (MS), with the main goal of testing for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and similar to 1 mm dust photometry, in a large sample of 1444 star-forming galaxies between z = 0 and 4. The sample covers the stellar mass range log(M-*/M-circle dot) = 9.0-11.8, and SFRs relative to that on the MS, delta MS = SFR/SFR (MS), from 10(-1.3) to 10(2.2). Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero-point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time t(depl), defined as the ratio of molecular gas mass to SFR, scales as (1 + z)(-0.6) x (delta MS)(-0.44) and is only weakly dependent on stellar mass. The ratio of molecular to stellar mass mu(gas) depends on (1+ z)(2.5) x (delta MS)(0.52) x (M-*)(-0.36), which tracks the evolution of the specific SFR. The redshift dependence of mu(gas) requires a curvature term, as may the mass dependences of t(depl) and mu(gas). We find no or only weak correlations of t(depl) and mu(gas) with optical size R or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high z.

We investigate the relationship between the black hole accretion rate (BHAR) and star formation rate (SFR) for Milky Way (MW) and Andromeda (M31)-mass progenitors from z = 0.2 to 2.5. We source galaxies from the K-s-band-selected ZFOURGE survey, which includes multiwavelength data spanning 0.3-160 mu m. We use decomposition software to split the observed spectral energy distributions (SEDs) of our galaxies into their active galactic nuclei (AGNs) and star-forming components, which allows us to estimate BHARs and SFRs from the infrared (IR). We perform tests to check the robustness of these estimates, including a comparison with BHARs and SFRs derived from X-ray stacking and far-IR analysis, respectively. We find that, as the progenitors evolve their relative black hole-galaxy growth (i.e. their BHAR/SFR ratio) increases from low to high redshift. The MW-mass progenitors exhibit a log-log slope of 0.64 +/- 0.11, while the M31-mass progenitors are 0.39 +/- 0.08. This result contrasts with previous studies that find an almost flat slope when adopting X-ray-/AGN-selected or mass-limited samples and is likely due to their use of a broad mixture of galaxies with different evolutionary histories. Our use of progenitor-matched samples highlights the potential importance of carefully selecting progenitors when searching for evolutionary relationships between BHAR/SFRs. Additionally, our finding that BHAR/SFR ratios do not track the rate at which progenitors quench casts doubts over the idea that the suppression of star formation is predominantly driven by luminous AGN feedback (i.e. high BHARs).