Dust is a critical component of the universe, affecting energy flow and the dynamics of star and planetary disk evolution. The light we measure when observing the universe is absorbed and scattered (extinguished) by dust. Studies indicate that active formation of high mass stars modifies the ultraviolet (UV) dust extinction curve, removing the characteristic bump at 2175 Å. For a half century, the source of this bump has not been positively identified. Dust grain models suggest that a leading contender is polycyclic aromatic hydrocarbons. The spiral galaxy M101 is an ideal laboratory, with many HII regions, plus steep metallicity and ionization gradients. The role of environment in this enigmatic "bump-less'' extinction was investigated in M101 with observations from both a sounding rocket mission and the Hubble Space Telescope (HST). The Interstellar Absorption Gradient Experiment Rocket (IMAGER) mission was designed to probe the correlations between dust extinction and environment through photometric observations of the apparent strengths of the 2175 Å bump and UV continuum in M101. IMAGER flew and collected data on November 21, 2012. Although in-flight anomalies caused significant cross-talk, the mission demonstrated the feasibility of simultaneous imaging in three medium-width UV bands. With angular resolution poorer than one arcminute in all bands, and inadequate signal in the field-of-view, these data proved unsuitable for aperture photometry. This analysis method cannot be used with these data to draw conclusions about the correlations between environment and ultraviolet extinction. Spectroscopic observations were performed with the Space Telescope Imaging Spectrograph (STIS) instrument aboard the HST. With additional data from the Spitzer Space Telescope, and radiative transfer and stellar evolution models, the correlation between the bump and the aromatic features was probed across HII regions spanning wide ranges of metallicity and radiation field hardness. A correlation between the strengths of the aromatic features and the 2175 Å feature was not found-- the statistics preclude a definitive statement regarding the origin of the bump. Many models of dust extinction are consistent with the data, implying a need for more observations of the feature and possibly a significant modification of the source of 2175 Å extinction in dust models.

This thesis is comprised of work carried out during the commissioning phase of Project 1640, a combined coronagraph--integral field spectrograph for Palomar Observatory's adaptive optics-equipped 200'' Hale Telescope. I have divided my investigations into three chapters. First, I describe the data reduction pipeline software, which solves a number of data extraction and calibration challenges unique to this kind of instrument. In the second chapter, I demonstrate a novel method for faint companion discovery which takes advantage of the high-precision relative astrometry enabled by a pupil plane reticle grid. This tool, in combination with the spectrophotometric capability of the integral field spectrograph, reveal that the A5V star Alcor has a heretofore unknown M-dwarf companion. In my third chapter, I explore the suitability of combining the non-redundant aperture mask interferometry technique with an integral field spectrograph. In the proof-of-concept observation of the spectroscopic binary star Beta CrB, I retrieve the first near-infrared spectrum of its F-dwarf companion.

Void galaxies, residing within the deepest underdensities of the Cosmic Web, present an ideal population for the study of galaxy formation and evolution in an environment undisturbed by the complex processes modifying galaxies in clusters and groups, and provide an observational test for theories of cosmological structure formation. We investigate the neutral hydrogen properties (i.e. content, morphology, kinematics) of void galaxies, both individually and systematically, using a combination of observations and simulations, to form a more complete understanding of the nature of these systems. We investigate in detail the H I morphology and kinematics of two void galaxies. One is an isolated polar disk galaxy in a diffuse cosmological wall situated between two voids. The considerable gas mass and apparent lack of stars in the polar disk, coupled with the general underdensity of the environment, supports recent theories of cold flow accretion as an alternate formation mechanism for polar disk galaxies. We also examine KK 246, the only confirmed galaxy located within the nearby Tully Void. It is a dwarf galaxy with an extremely extended H I disk and signs of an H I cloud with anomalous velocity. It also exhibits clear misalignment between the kinematical major and minor axes, and a general misalignment between the H I and optical major axes. The relative isolation and extreme underdense environment make these both very interesting cases for examining the role of gas accretion in galaxy evolution. To study void galaxies as a population, we have carefully selected a sample of 60 galaxies that reside in the deepest underdensities of geometrically identified voids within the SDSS. We have imaged this new Void Galaxy Survey in H I at the Westerbork Synthesis Radio Telescope with a typical resolution of 8 kpc, probing a volume of 1.2 Mpc and 12,000 km s^-1 surrounding each galaxy. We reach H I mass limits of 2 x 10^8 M_sun and column density sensitivities of 5 x 10^19 cm^-2. We find that the void galaxies are generally gas rich, low luminosity, blue disk galaxies, but identify three as early type galaxies. The void galaxy optical and H I properties are not unusual for their luminosity and morphology. The small scale clustering in the void is similar to that in higher density regions, and we identify 18 H I rich neighboring galaxies in the voids. Two of these are systems of three galaxies linearly aligned and joined by a H I bridge, suggestive of filamentary formation within the void. We find no population of H I rich low luminosity galaxies within the observed voids that are not close companions of the targeted sample. Finally, to put these observations in a theoretical context, we analyze a (120 h^-1 Mpc)^3 adaptive mesh refinement hydrodynamic simulation that contains a high resolution subvolume centered on a ~30 Mpc diameter void. We construct mock observations with ~1 kpc resolution of the stellar and gas properties of these systems which reproduce the range of colors and luminosities observed in the SDSS for nearby galaxies, however we find no strong trends with density. We also make predictions for a significant population of low luminosity (M_r = -14) dwarf galaxies that is preferentially located in low density regions and specifically in the void center.

In this dissertation, I explore the subject of short-period binary millisecond pulsars discovered by the Fermi Gamma-ray Space Telescope and radio follow-up teams, and present observations of fields containing eight recently discovered short-period (Porb < 1 d) binary millisecond pulsars using the telescopes at MDM Observatory. The goal of these observations was to detect the optical counterparts of the binaries and, for the best-suited counterparts detected, to observe the photometric variation of the companion that happens over the course of the orbit in various filters. The hope was to then use the light curves to model the systems and obtain constraints on the mass of the neutron stars which are likely to be some of the most massive neutron stars in the galaxy. Optical counterparts to four of these systems are detected, one of which, PSR J2214+3000, is a novel detection. Additionally, I present the fully orbital phase-resolved B, V , and R light curves of the optical counterparts to two objects, PSR J1810+1744 and PSR J2215+5135, for which I employ the ELC model of Orosz & Hauschildt (2000) to measure the unknown system parameters. For PSR J1810+1744 I find that the system parameters cannot be fit even assuming that 100% of the spin-down luminosity of the pulsar is irradiating the secondary, and so radial velocity measurements of this object will be required for the complete solution. However, PSR J2215+5135 exhibits light curves that are extremely well constrained using the ELC model and we find that the mass of the neutron star is constrained by these and the radio observations to be MNS > 1.75 solar masses; at the 3-sigma level. I also find a discrepancy between the model temperature and the measured colors of this object which I interpret as possible evidence for an additional high-temperature source such as a quiescent disk. Given this and the fact that PSR J2215+5135 contains a relatively high mass companion (Mc > 0.1 solar masses), I propose that similar to the binary pulsar systems PSR J1023+0038 and IGR J18245-2452, the pulsar may transition between accretion- and rotation-powered modes.

The diffuse universe, consisting of baryons that have not yet collapsed into structures such as stars, galaxies, etc., has not been well studied. While the intergalactic and circumgalactic mediums (IGM & CGM) may contain 30-40% of the baryons in the universe, this low density gas is difficult to observe. Yet it is likely a key driver of the evolution of galaxies and star formation through cosmic time. The IGM provides a reservoir of gas that can be used for star formation, if it is able to accrete onto a galaxy. The CGM bridges the IGM and the galaxy itself, as a region of both inflows from the IGM and outflows from galactic star formation and feedback. The diffuse interstellar medium (ISM) gas and dust in the galaxy itself may also be affected by the CGM of the galaxy. Careful observations of the ISM of our own Galaxy may provide evidence of interaction with the CGM. These three regions of low density, the IGM, CGM, and ISM, are arbitrary divisions of a continuous flow of low density material into and out of galaxies. My thesis focuses on observations of this low density material using existing telescopes as well as on the development of technology and instruments that will increase the sensitivity of future missions. I used data from the Galaxy Evolution Explorer (GALEX) to create an all sky map of the diffuse Galactic far ultraviolet (FUV) background, probing the ISM of our own galaxy and comparing to other Galactic all sky maps. The FUV background is primarily due to dust scattered starlight from bright stars in the Galactic plane, and the changing intensity across the sky can be used to characterize dust scattering asymmetry and albedo. We measure a consistent low level non-scattered isotropic component to the diffuse FUV, which may be due in small part to an extragalactic component. There are also several regions of unusually high FUV intensity given other Galactic quantities. Such regions may be the location of interactions between Galactic super-bubbles and the CGM. Other ways of probing the CGM including direct detection via emission lines. I built a proto-type of the Circumgalactic Hα Spectrograph (CHαS), a wide-field, low-cost, narrow-band integral field unit (IFU) that is designed to observe Hα emission from the CGM of nearby, low-z galaxies. This proto-type has had two recent science runs, with preliminary data on several nearby galaxies. Additional probes of the CGM are emission lines in the rest ultra-violet. These include OVI, Lyα, CIV, SiIII, CIII, CII, FeII, and MgII. Such lines are accessible for low redshift galaxies in the space UV, historically a difficult wavelength range in which to work due in part to low efficiency of the available detectors. I have worked with NASA's Jet Propulsion Laboratory to develop advanced anti-reflection (AR) coatings for use on thinned, delta-doped charge coupled device (CCD) detectors. These detectors have achieved world record quantum efficiency (QE) at UV wavelengths (> 50% between 130 nm and 300nm), with the potential for even greater QE with a more complex coating. One of these AR coated detectors will be used on the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2), a balloon-born UV spectrograph designed to observe the CGM at 205 nm via redshifted Lyα (at z=0.7), CIV (at z=0.3), and OVI (at z=1.0). FIREBall-2 will launch in the fall of 2015.

Cold gas is fundamental in understanding galaxy formation and evolution since it provides the fuel for star formation. In addition, the atomic gas can be used to probe the internal properties of galaxies, their halos, and their environment. Several of the remaining questions in galaxy evolution can be addressed by studying the gas properties in galaxies, in particular, the following three: (1) How do galaxies get their gas? (2) How do galaxies change over time? (3) How are galaxies affected by the environment? The work presented in this thesis addresses these questions. The thesis is divided into three parts that cover a range of topics related to gas in galaxies, including the fate of gas in a merger remnant, the evolution and distribution of halo gas, and how the gas properties of galaxies change as a function of redshift and environment. Part I consists of two chapters that present the atomic and molecular gas properties of a wet merger remnant (NGC 34). Chapter 2 is an analysis of the HI distribution and kinematics in NGC 34. We find that the progenitors of NGC 34 were gas-rich. The kinematics of the tidal tails suggest that some of the gas is returning to the central regions and forming an outer disk. In addition, we find puzzling absorption near the systemic velocity against the radio continuum. Chapter 3 is a follow-up study consisting of CO observations done with CARMA and new VLA data with a large velocity coverage to search for outflows. We detect CO concentrated in the inner regions that matches the velocity range of the HI in absorption, indicating that there is a circumnuclear disk in the central regions of molecular and atomic gas. We do not detect the outflow seen in the optical spectrum in CO or HI, but are able to place upper limits on both. Part II is an analysis of halo gas in a Milky Way mass galaxy. We use a cosmological high resolution hydrodynamic simulation to study the distribution, origin, and evolution of halo gas. At z=0, we find that the amount (~ 10⁸ M_sun), covering fraction and distribution are consistent with existing observations. The origin of halo gas is a combination of filamentary and satellite material. In addition, we find that the amount of halo gas is roughly constant between z=0.3 to z=0, but increases at earlier times. Part III presents results from the COSMOS HI Large Extragalactic Survey (CHILES), an HI deep field done with the VLA. These observations show how galaxies grow in different environments across cosmic time. We are using the expanded capabilities of the VLA to probe HI in part of the COSMOS field with a 5" resolution. Chapter 5 presents results from the pilot that was observed during commissioning. We observed for 60 hr and covered the redshift range 0<z<0.19 in one setting. We report 33 direct detections in different environments across the redshift range, and a stacked HI mass of (1.8 ± 0.3) x 10⁹ M_sun for galaxies in a wall at z=0.12. The pilot demonstrated that the VLA was ready to carry a full HI deep field. The full survey will be 1002 hr spread over several B array configurations. Chapter 6 presents preliminary results for the first 178 hr of the survey (Phase I). We describe the data reduction from Phase I, lessons for upcoming configurations, and present preliminary results. We detect very extended HI disks in nearby dwarf galaxies, and present the highest redshift detection to date (z=0.376).

This dissertation consists of several projects designed to further our understanding of galaxies and galactic structures associated with intervening quasar absorption lines -- i.e., those selected via gas cross section. Surveys for MgII absorption were conducted utilizing QSO spectra from the Sloan Digital Sky Survey and data collected at the 6.5m Multiple Mirror Telescope Observatory on Mount Hopkins, AZ. The first survey expands the number of studied MgII systems by an order of magnitude, while the second extends the statistics to weaker systems and lower redshifts. The results provide high-precision measurements of the statistics and evolution of MgII absorbers. It is shown that the distribution of rest equivalent width steepens with decreasing redshift, especially at redshifts z<1, such that the total absorption co-moving cross section decreases at a rate proportional to rest equivalent width. This is interpreted as an evolution in the kinematic properties of the absorbing galaxy population. Evidence for multiple physical populations comprising MgII absorbers is presented and discussed. Early survey results were used to investigate the cosmic neutral-gas-phase metallicity and dust content. QSO spectra selected due to the presence of strong intervening MgII absorption were stacked in the absorption rest frame to create high signal-to-noise ratio composites with which to measure Zn and Cr abundances. It was found that metallicity of high-N(HI) gas is highly correlated with the kinematic properties of galaxies and both metallicity and dust content for these systems increase with decreasing redshift. Two projects were completed that involved the imaging of six low-redshift damped Lyman-alpha galaxies. Detailed properties of the identified absorber galaxies are described. They are shown to be drawn from a variety of morphological types with a range of luminosities, environments, and impact parameters.

We present new spectroscopy and Hubble Space Telescope imaging of protostellar jets discovered in an Hαsurvey of the Carina Nebula. Near-IR [Fe II] emission from these jets traces dense gas that is self-shielded from Lyman continuum photons from nearby O-type stars, but is excited by non-ionizing FUV photons that penetrate the ionization front within the jet. New near-IR [Fe II] images reveal a substantial mass of dense, neutral gas that is not seen in Hαemission from these jets. In some cases, [Fe II] emission traces the jet inside its natal dust pillar, connecting the larger Hαoutflow to the embedded IR source that drives it. New proper motion measurements reveal tangential velocities similar to those typically measured in lower-luminosity sources (100−200 km/s⁻¹). Combining high jet densities and fast outflow speeds leads to mass-loss rate estimates an order of magnitude higher than those derived from the Hαemission measure alone. Higher jet mass-loss rates require higher accretion rates, implying that these jets are driven by intermediate-mass (~ 2−8 M⊙) protostars. For some sources, the mid-IR luminosities of the driving sources are clearly consistent with intermediate-mass protostars; others remain deeply embedded and require long-wavelength, high-resolution images to confirm their luminosity. These outflows are all highly collimated, with opening angles of only a few degrees. With this new view of collimated jets from intermediate-mass protostars, we argue that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core and the material it sweeps up are irradiated and rendered observable. Thus, the jets in Carina offer strong additional evidence that stars up to ~ 8 M⊙ form by the same accretion mechanisms as low-mass stars.

One of the most compelling scientific quests ever undertaken is the quest to find life in our Universe somewhere other than Earth. An important piece to this puzzle is finding and characterizing extrasolar planets. This effort, particularly the characterization step, requires the ability to directly image such planets. This is a challenging task - such planets are much fainter than their host stars. One of the major solutions to this problem is Adaptive Optics (AO), which allows us to correct the turbulence in the Earth's atmosphere, and thereby further the hunt for exoplanets with ground based telescopes. The Magellan Adaptive Optics system has recently obtained its first on-sky results at Las Campanas Observatory, marking a significant step forward in the development of high-resolution high-contrast ground-based direct imaging. MagAO includes a visible wavelength science camera, VisAO, which - for the first time - provides diffraction limited imaging, in long exposures, on a large filled-aperture (6.5 m) telescope. In this dissertation we report on the design, development, laboratory testing, and initial on-sky results of MagAO and VisAO, which include the first ground-based image of an exoplanet (beta Pictoris b) with a CCD. We also discuss some of the exciting science planned for this system now that it is operational. We close with an analysis of a new problem in direct imaging: planets orbiting their stars move fast enough in the habitable zone to limit our ability to detect them.

What physical processes and sources of material contribute to exoplanet compositions? Specifically, what roles do the protoplanetary disk composition and structure, and host star abundances play in the different stages of planet formation? In this thesis, beginning with a brief literature review in Chapter 2, I trace oxygen and carbon species through these stages to inform how, when, and where planets form. In Chapter 3 I describe a study of the molecular emission from the warm inner disks of T Tauri stars, where terrestrial planets likely form. I report moderate correlations between HCN emission strength and both stellar accretion rate (measured from UV or optical excess emission associated with accretion) and X-ray luminosity. These correlations point towards accretion related processes being an important source of disk atmosphere heating, and suggests that efficient H₂O formation and/or UV dissociation of N₂ (both also associated with higher stellar accretion rates) may aid in the production of HCN. Studies following mine have further connected the abundance of HCN versus H₂O to the growth and migration of planetesimals in the disk, which helps control the formation of both giant and terrestrial planets. I shift to an already-formed exoplanet in Chapter 4, where I present optical photometry of the best-observed transiting super-Earth GJ 1214b with the goal of constraining the short-wavelength slope of its transmission spectrum. Most previous observations suggested a flat spectrum from the near-IR to the optical, corresponding to a low-scale-height, high-molecular-weight atmosphere. My observations are in general agreement with these findings, keeping the "door open" for a H₂O-rich atmosphere for GJ 1214b, which other published g-band observations appeared to contradict. Chapters 5-7 of my thesis focus on measuring stellar abundances, particularly C/O ratios, in transiting (mostly) hot Jupiter exoplanet host stars from high resolution optical spectroscopy. Host star abundances may indicate the precursor materials present in the disk and available for incorporation into planets. In hot Jupiters, the C/O ratio affects the partitioning of C in the major observable molecules, making C and O diagnostic of temperature structure and composition. I also demonstrate that extra caution is necessary in deriving carbon and oxygen abundances, especially for cool and metal-rich stars. Though exoplanetary C/O ratios are still uncertain, the more precise abundance analysis possible right now for their host stars can help constrain their formation environments and current compositions. I summarize my graduate school research in Chapter 8, and discuss the next steps I will take in my postdoctoral career.