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Publication Clearing the Path to Cosmic Reionization(2024-09) Flury, SophiaObservations indicate a phase change of the Universe from neutral back to ionized after the first billion years of cosmic time (z ∼ 6). Two great unknowns persist regarding this cosmic reionization: what caused it, and how? Using a sample of nearby (z ∼ 0.3) galaxies, I answer these questions. First, I undertake careful measurements of the emergent ionizing radiation and other properties of 89 galaxies. Then, I compare the escape of this ionizing radiation to those properties, finding small, faint galaxies with concentrated star formation are the most prodigious ionizing radiation emitters. To understand the role of star formation in the escape of ionizing radiation, I develop a new method for modeling galactic winds that connects feedback mechanisms and outflow properties with observations. Finally, I characterize the stellar populations, the interstellar material, and the interplay between them in galaxies leaking ionizing radiation. I find that bursty star formation optimizes feedback for ionizing radiation escape from galaxies. The application of my results to recent observations of high redshift galaxies provides the first empirical constraints on the progenitors of ionizing radiation in the early Universe. Bridging the gap between my low-redshift works and distant galaxies clears a path to understanding the origins of cosmic reionization.Publication Development of the TolTEC Data Reduction Pipeline and the Application of Hierarchical Bayesian Inference to TolTEC Data(2024-05) McCrackan, Michael JTolTEC is a millimeter-wavelength imaging polarimeter now installed on the 50-meter Large Millimeter Telescope that simultaneously maps the sky using 7718 dual- polarization Lumped Element Kinetic Inductance Detectors distributed among three monochromatic arrays, centered at 1.1, 1.4, and 2.0 mm (273, 214, and 150 GHz). The camera is currently in the commissioning phase and has completed two observational runs, in June and December of 2022. This work offers a comprehensive review of the TolTEC data reduction and mapmaking pipeline Citlali (v4.0), an open-source, high-performance, and parallelized software package written in C++. Citlali rapidly transforms the raw time-ordered data from all categories of TolTEC data into two-dimensional maps of the sky, in addition to performing map coaddition and post-mapmaking point source filtering. The pipeline’s design philosophy, data streaming and parallelization model, timestream reduction stages, mapmaking algorithms, and iterative mapmaking routine are detailed. Maps of sources observed during TolTEC’s 2022 commissioning, including the radio quasar J1159+292, the Crab Nebula, and the Monoceros R2 Giant Molecular Cloud, which were produced using Citlali, are presented. The analysis investigates the flux recovery from extended sources by Citlali’s iterative mapmaker and compares results from the built-in mapmakers to maps created with the maximum likelihood mapmaker Minkasi. This work also details a C++ hierarchical Bayesian MCMC software package developed for fitting dust emission SEDs in each pixel of TolTEC maps. This code integrates instrumental PSF data into a forward-fitting model to maintain contributions from higher-resolution observations within the dataset. Both modified blackbody and physically motivated dust models using the Astrodust+PAH model of Hensley and Draine 2023 have been implemented. Results from applying this software to simulated dust SEDs, as well as to WISE, Spitzer, and Herschel observations of the face-on spiral galaxy NGC 3938, are presented.Publication Characterizing Distant Galaxies: Spectral Energy Distribution Analysis of X-ray Selected Star Forming Galaxies(2013-09) Johnson, Seth PohatanComprehensive and robust analysis of galaxies found throughout cosmic time provides the means to probe the underlying characteristics of our Universe. Coupling observations and theory, spectral energy distribution (SED) fitting provides a method to derive the intrinsic properties of distant galaxies which then aid in defining galaxy populations and constraining current galaxy formation and evolution scenarios. One such population are the sub-millimeter galaxies (SMGs) whose high infrared luminosities -- typically associated with dust-obscured star formation -- and redshift distribution places them as likely key components in galaxy evolution. To fully analyze these systems, however, requires a near complete sampling of the full SED, detailed models that encapsulate the variety of physical processes and sophisticated methods for comparing the data and models. In this dissertation, we present the general propose, Monte Carlo Markov Chain (MCMC) based SED fitting routine SED Analysis Through Markov Chains (SATMC) and the insight we have gained in modeling a sample of AzTEC 1.1mm-detected SMGs. The MCMC engine and Bayesian formalism used in the construction of SATMC offers a unique view at the constraints on model parameter space that are often grossly simplified in traditional SED fitting methods. We first present the motivation behind SATMC and its MCMC algorithm. We also highlight a series of test cases that verify not only its reliability but its versatility to various astrophysical applications, including the field of photometric redshift estimation. We then present the AzTEC SMG sample and preliminary results obtained through counterpart identification, X-ray spectral modeling and SED fitting with SATMC. Finally, we present the latest work in detailed SED analysis of SMGs and how these results influence our understanding of the SMG population.Publication Bayesian Anatomy of Galaxy Structure(2013-02) Yoon, IlsangIn this thesis I develop Bayesian approach to model galaxy surface brightness and apply it to a bulge-disc decomposition analysis of galaxies in near-infrared band, from Two Micron All Sky Survey (2MASS). The thesis has three main parts. First part is a technical development of Bayesian galaxy image decomposition package Galphat based on Markov chain Monte Carlo algorithm. I implement a fast and accurate galaxy model image generation algorithm to reduce computation time and make Bayesian approach feasible for real science analysis using large ensemble of galaxies. I perform a benchmark test of Galphat and demonstrate significant improvement in parameter estimation with a correct statistical confidence. Second part is a performance test for full Bayesian application to galaxy bulgedisc decomposition analysis including not only the parameter estimation but also the model comparison to classify different galaxy population. The test demonstrates that Galphat has enough statistical power to make a reliable model inference using galaxy photometric survey data. Bayesian prior update is also tested for parameter estimation and Bayes factor model comparison and it shows that informative prior significantly improves the model inference in every aspects. Last part is a Bayesian bulge-disc decomposition analysis using 2MASS Ks-band selected samples. I characterise the luminosity distributions in spheroids, bulges and discs separately in the local Universe and study the galaxy morphology correlation, by full utilising the ensemble parameter posterior of the entire galaxy samples. It shows that to avoid a biased inference, the parameter covariance and model degeneracy has to be carefully characterised by the full probability distribution.Publication A Frequency Selective Bolometer Camera for Measuring Millimeter Spectral Energy Distributions(2009-05) Logan, Daniel WilliamBolometers are the most sensitive detectors for measuring millimeter and submillimeter wavelength astrophysical signals. Cameras comprised of arrays of bolometers have already made significant contributions to the field of astronomy. A challenge for bolometer cameras is obtaining observations at multiple wavelengths. Traditionally, observing in multiple bands requires a partial disassembly of the instrument to replace bandpass filters, a task which prevents immediate spectral interrogation of a source. More complex cameras have been constructed to observe in several bands using beam splitters and dichroic filters, but the added complexity leads to physically larger instruments with reduced efficiencies. The SPEctral Energy Distribution camera (SPEED) is a new type of bolometer camera designed to efficiently observe in multiple wavebands without the need for excess bandpass filters and beam splitters. SPEED is a ground-based millimeter-wave bolometer camera designed to observe at 2.1, 1.3, 1.1, and 0.85 mm simultaneously. SPEED makes use of a new type of bolometer, the frequency selective bolometer (FSB), to observe all of the wavebands within each of the camera's four pixels. FSBs incorporate frequency selective dipole surfaces as absorbing elements allowing each detector to absorb a single, narrow band of radiation and pass all other radiation with low loss. Each FSB also contains a superconducting transition-edge sensor (TES) that acts as a sensitive thermistor for measuring the temperature of the FSB. This thesis describes the development of the SPEED camera and FSB detectors. The design of the detectors used in the instrument is described as well as the the general optical performance of frequency selective dipole surfaces. Laboratory results of both the optical and thermal properties of millimeter-wave FSBs are also presented. The SPEED instrument and its components are highlighted and the optical design of the optics which couple SPEED to the Heinrich Hertz Telescope is given. This thesis concludes with an introduction to the jiggle mapping data analysis of bolometer instruments like SPEED.Publication The Assembly of Galaxies Over Cosmic Time(2012-09) Guo, YichengTo Understand how galaxies were assembled across the cosmic time remains one of the most outstanding questions in astronomy. The core of this question is how today's Hubble Sequence, namely the differentiation of galaxy morphology and its correlation to galaxy physical properties, is formed. In this thesis, we investigate the origin of the Hubble Sequence through galaxies at z~2, an epoch when the cosmic star formation activity reaches its peak and the properties of galaxies undergo dramatic transitions. Galaxies at z~2 have two important features that are distinct from nearby galaxies: much higher frequency of clumpy morphology in star-forming systems, and much compacter size. To understand the nature of the two features requires investigations on the sub-structure of galaxies in a multi-wavelength way. In this thesis, we study samples of galaxies that are selected from GOODS and HUDF, where ultra-deep and high-resolution optical and near-infrared images allow us to study the stellar populations of the sub-structures of galaxies at the rest-frame optical bands for the first time, to answer two questions: (1) the nature of kiloparsec-scale clumps in star-forming galaxies at z$\sim$2 and (2) the existence of color gradient and stellar population gradient in passively evolving galaxies at z~2, which may provide clues to the mechanisms of dramatic size evolution of this type of galaxies. We further design a set of color selection criteria to search for dusty star-forming galaxies and passively evolving galaxies at z~3 to explore the question: when today's Hubble Sequence has begun to appear.Publication Infrared and X-ray Studies of the Galactic Center(2011-09) Dong, HuiThe purpose of this dissertation is to locate evolved massive stars within the central 50 pc of the Galactic Center. These stars are considered to be the descendants of O stars and should be less than 10 Myr old. They trace young star clusters within the Galactic Center. Through these stars and young star clusters, we hope to understand the star formation mode and history within the Galactic Center, as well as the properties of evolved massive stars in the high metallicity environment. We first study the Chandra X-ray deep survey of the Arches and Quintuplet clusters, two of the three young massive star clusters within the Galactic Center. The diffuse X-ray emission is used to constrain their initial mass function and we find a deficiency of low-mass stars, which could be explained by an ongoing collision between the clusters and the adjacent molecular clouds. We then perform a systematic search of young massive stars on a large scale within the Galactic Center through our new HST/NICMOS Paschen-alpha survey. We produce mosaic maps of the Paschen-alpha line and continuum emission, giving an unprecedentedly high resolution and high sensitivity panoramic view of stars and photo-ionized gas in the nuclear environment of the Galaxy. Many new HII regions and extended emission regions have been found. Combined with the archived HST snapshot observations and spectroscopic observations, we construct a sample of 180 potentially evolved massive stars. A multi-wavelength study of these stars is conducted. We find that young massive stars have continued to form within the Galactic Center during the last 10 Myr and some of the evolved massive stars may represent star formation in small groups or even in isolation, compared to the three massive star clusters within the Galactic CenterPublication High-resolution Ultraviolet Spectroscopy of Gas in Galaxy Halos and Large-scale Structures(2011-02) Song, LiminThis dissertation presents spectroscopic studies of gas in galaxy halos and large-scale structures through high-resolution quasar absorption lines. The broad goal of this effort is to learn how galaxies acquire their gas and how they return it to the intergalactic medium, or more generally, how galaxies interact with their environment. The study of the absorption lines due to the extraplanar 21cm "Outer Arm'' (OA) of the Milky Way toward two quasars, H1821+643 and HS0624+6907, provides valuable insight into the gas accretion processes. It yields the following results. (1) The OA is a multiphase cloud and high ions show small but significant offsets in velocity and are unlikely to be cospatial with the low ions. (2) The overall metallicity of the OA is Z=0.3-0.5 of the solar abundance, but nitrogen is underabundant. (3) The abundance of N, O, and S derived are roughly consistent with outer-galaxy emission-line abundances and the metallicity gradient derived from H II regions. The similarity of the OA kinematics to several nearby high velocity clouds (HVCs, e.g. Complexes C, G, and H) suggests that these clouds could be detritus from a merging satellite galaxy. To test this hypothesis, we build up a simple model including tidal tripping, ram-pressure stripping, and dynamical friction to consider whether the OA could be debris affiliated with the Monoceros Ring. Our model can roughly reproduce the spatial and velocity characteristics of the OA. Moreover, the metallicity of the OA is similar to the higher metallcities measured in the younger stellar components of the Monoceros Ring and the progenitor candidate, the CMa overdensity. However, both our model and the Galactic warp scenario can not explain other HVCs that are likely to be related to the OA. Instead of acquiring gas, some galaxies have their gas removed through various physical processes. Ram-pressure stripping and tidal interaction are important mechanisms for galaxies to loose their gas. The high-resolution spectrum of Mrk205 combined with H I 21 cm, CO emission, and infrared observations is utilized to study a unique transforming galaxy NGC4319. We find: (1) the object has lost most of its diffuse interstellar H I. (2) molecular hydrogen remains in the disk of the galaxy. The molecular hydrogen column density is low, but the molecular gas fraction is extraordinarily high. CO emission is also clearly detected, but only from the barred central region. (3) There is very little evidence of recent star formation in the galaxy. The results appears to match many of the predictions of Quilis et al. (2000), suggesting NGC4319 is undergoing a transformation from a spiral into an S0 due to ram-pressure stripping, possibly in tandem with tidal stripping. To understand the characteristics of gas (especially warm-hot intergalactic medium) in large scale structures, similar high resolution spectra of 31 quasars were selected based on the galaxy density showing in the 2MASS map. They provide a unbiased sample for the study of the correlation between O VI/H I absorbers and galaxies and 2MASS galaxy groups at low redshift (z<0.04). We totally discover 52 \lya\ absorbers and 7 O VI absorbers, and O VI is clearly detected using the stacking and "pixel optical depth'' techniques for nearby galaxies along the sightlines. It seems that the locations of the O VI absorbers do not correlated with the spacial distribution of large-scale structures manifested by galaxy groups, but more closely associated with individual galaxies. It indicates that the galactic winds and "feedback'' plays important role in polluting the IGM with O VI. Finally, we perform an extra investigation on the variable O VI and N V emission from the black hole binary LMC X-3 in our original absorption line study of the hot Galactic halo and the ISM of the LMC using LMC X-3 as a background source. We observe significant velocity and intensity variation in both O VI and N V emission. Their trends suggest that illumination of the B-star atmosphere by the intense X-ray emission from the accreting black hole creates a hot spot on one side of the B star, and this hot spot is the origin of the O VI and N V emission.Publication The AzTEC Millimeter-wave Camera: Design, Integration, Performance, and the Characterization of the (sub-)millimeter Galaxy Population(2009-05) Austermann, Jason EdwardOne of the primary drivers in the development of large format millimeter detector arrays is the study of sub-millimeter galaxies (SMGs) - a population of very luminous high-redshift dust-obscured starbursts that are widely believed to be the dominant contributor to the Far-Infrared Background (FIB). The characterization of such a population requires the ability to map large patches of the (sub-)millimeter sky to high sensitivity within a feasible amount of time. I present this dissertation on the design, integration, and characterization of the 144-pixel AzTEC millimeter-wave camera and its application to the study of the sub-millimeter galaxy population. In particular, I present an unprecedented characterization of the "blank-field" (fields with no known mass bias) SMG number counts by mapping over 0.5 deg 2 to 1.1mm depths of ∼1mJy - a previously unattained depth on these scales. This survey provides the tightest SMG number counts available, particularly for the brightest and rarest SMGs that require large survey areas for a significant number of detections. These counts are compared to the predictions of various models of the evolving mm/sub-mm source population, providing important constraints for the ongoing refinement of semi-analytic and hydrodynamical models of galaxy formation. I also present the results of an AzTEC 0.15 deg 2 survey of the COSMOS field, which uncovers a significant over-density of bright SMGs that are spatially correlated to foreground mass structures, presumably as a result of gravitational lensing. Finally, I compare the results of the available SMG surveys completed to date and explore the effects of cosmic variance on the interpretation of individual surveys.Publication Dark Matter Halos: Assembly, Clustering and Sub-halo Accretion(2010-02) Li, YunI carried out systematic studies on the assembly history of dark matter halos, using numerical simulations and semi-analytical methods. First, I look into dark halo mass assembly history. I confirmed that the halo mass assembly is divided into a fast accretion phase and a slow accretion phase. These two phases are found to be separated by the epoch when the dark halo potential reaches its maximum. The fast accretion phase is dominated by mergers, especially major mergers; the slow accretion phase is dominated by slow mass accretion. Each halo experiences about 3±2 major mergers since its main progenitor had a mass equal to 1 percent of halo mass. However, the average redshift at which these major mergers occur is strongly mass dependent. Secondly, I investigate the formation times and the assembly bias of dark halos. I use eight different definitions of halo formation times to characterize the different aspects of the halo assembly history. I find that these formation times have different dependence on halo mass. While some formation times characterize well the hierarchical nature of halo formation, the trend is reversed for other definitions of the formation time. In addition, the formation-time dependence of halo bias is quite strong for some definitions of formation time but weak or absent for others. Thirdly, I study sub-halo mass function in the halo assembly history, with the generally known unevolved sub-halo mass functions (USMFs). I find that for subhalos that merge into the main progenitor of a present-day halo, their USMF can be well described by a universal functional form; the same conclusion can also be reached for the USMF of all sub-halos that have merged during the entire halo merging history. In these two cases, the USMFs do not seem to depend on the redshift of the host halo either. However, due to the mass loss caused by dynamical effects, only small part of the accreted halos survived and became sub-structures in the present-day dark halos. In the cluster-sized halos, 30% survived sub-halos are sub-subhalos. The sub-halo mass function at given accretion time (redshift) is also investigated to find the origin of the statistics mentioned above.Publication The Role of Stellar Feedback in Galaxy Evolution(2009-02) Zhiyuan, LiAiming at understanding the role of stellar feedback in galaxy evolution, I present a study of the hot interstellar medium in several representative galaxies, based primarily on X-ray observations as well as theoretical modelling. I find that, in the massive disk galaxies NGC2613 and M104, the observed amount of hot gas is much less than that predicted by current galaxy formation models. Such a discrepancy suggests a lack of appropriate treatments of stellar/AGN feedback in these models. I also find that stellar feedback, primarily in the form of mass loss from evolved stars and energy released from supernovae, and presumably consumed by the hot gas, is largely absent from the inner regions of M104, a galaxy of a substantial content of evolved stars but little current star formation. A natural understanding of this phenomenon is that the hot gas is in the form of a galactic-scale outflow, by which the bulk of the stellar feedback is transported to the outer regions and perhaps into the intergalactic space. A comparison between the observed sub-galactic gas structures and model predictions indicate that this outflow is probably subsonic rather than being a classical supersonic galactic wind. Such outflows are likely prevalent in most early-type galaxies of intermediate masses in the present-day universe and thus play a crucial role in the evolution of such galaxies. For the first time I identify the presence of diffuse hot gas in and around the bulge of the Andromeda Galaxy (M31), our well-known neighbor. Both the morphology and energetics of the hot gas suggest that it is also in the form of a large-scale outflow. Assisted with multiwavelength observations toward the circumnuclear regions of M31, I further reveal the relation between the hot gas and other cooler phases of the interstellar medium. I suggest that thermal evaporation, mostly likely energized by Type Ia supernovae, acts to continuously turn cold gas into hot, a process that naturally leads to the inactivity of the central supermassive blackhole as well as the launch of the hot gas outflow. Such a mechanism plays an important role in regulating the multi-phase interstellar medium in the circumnuclear environment and transporting stellar feedback to the outer galactic regions.Publication Galactic Bulge Feedback and its Impact on Galaxy Evolution(2009-09) Tang, ShikuiGalactic bulges of early-type spirals and elliptical galaxies comprise primarily old stars, which account for more than half of the total stellar mass in the local Universe. These stars collectively generate a long-lasting feedback via stellar mass loss and Type Ia supernovae. According to the empirical stellar mass loss and supernova rates, the stellar ejecta can be heated to more than 107 K, forming a very hot, diffuse, and ironrich interstellar medium. Conventionally a strong galactic wind is expected, especially in low- and intermediate-mass early-type galaxies which have a relatively shallow potential well. X-ray observations, however, have revealed that both the temperature and iron abundance of the interstellar medium in such galaxies are unexpectedly low, leading to the so-called “missing feedback” and “missing metal” problems. As an effort to address the above outstanding issues, we have carried out a series of hydrodynamic simulations of galactic bulge feedback on various scales. On galactic halo scales, we demonstrate that the feedback from galactic bulges can play an essential role in the halo gas dynamics and the evolution of their host galaxies. We approximately divide the bulge stellar feedback into two phases: 1) a starbusrtinduced blastwave from the formation of the bulge built up through frequent major mergers at high redshifts and 2) a gradual feedback from long-lived low mass stars. The combination of the two can heat the surrounding gas beyond the virial radius and stop further gas accretion, which naturally produces a baryon deficit around Milky Way-like galaxies and explains the lack of large-scale X-ray halos. On galactic bulge scales, we study the collective 3-dimensional effects of supernovae with their blastwaves resolved. We find that the sporadic explosions of supernovae can produce a wealth of substructures in the diffuse hot gas and significantly affect the spectroscopic properties of the X-ray-emitting gas. The differential emission measure in the temperature space has a broad lognormal-like distribution. Such distribution enhances the X-ray emission at both low and high energy bands. We further show that the SN Ia ejecta is not well-mixed with the ambient medium and the X-ray emission is primarily from the shocked stellar wind materials which in general have low metallicities. These 3-dimensional effects provide a promising explanation to the above “missing feedback” and “missing metal” problems. In addition, we demonstrate that the supernova iron ejecta forms a very hot bubbles, which have relatively larger radial velocities driven by buoyancy, resulting in a smaller iron mass fraction in the bulk outflow. These distinct properties give a natural explanation to the observed positive iron abundance gradient which has been a puzzle for decades.Publication Astrophysical Accretion and Feedback: The Bayesian Linchpin of Theory and Observation(2017) Roberts, ShawnDespite being a major pillar of galaxy evolution, galactic feedback from stars and supermassive black holes (SMBHs) is subject to very little observational constraint. This is particularly true of the hot component, as viewed in X-rays. Yet, the hot component is directly linked to much of the energetic feedback released from these compact objects. X-ray observations suffer from several challenges that make placing this constraint a difficult task. In the face of considerable model uncertainty, these challenges underscore the need for novel X-ray data analysis techniques. In this dissertation, I seek to lend a unique perspective to X-ray data analysis and initiate the steps towards unravelling the hot component of galactic feedback. This is done through spatio-spectral fitting with Markov Chain Monte Carlo (MCMC). First, I fit 2D simulations of SMBH accretion to three separate bands of Chandra imaging data of Sgr A*, the SMBH at our galactic center. In this study I place the first observational constraint on the angular momentum of accreting gas and self-consistently deconvolve residual point-like emission from the spatially extended accretion flow. I extend this analysis in Appendix 2 by re-examining the spectral energy distribution of Sgr A* from radio to X-ray. I find that a 1D accretion flow model cannot be reconciled with the more detailed X-ray modelling results. I further speculate on the origin of very steep synchrotron emission, suggesting that the residual point-like emission is accelerated by magnetic turbulence. Second, I describe the methodology for extracting spatial information from the RGS grating spectrometer onboard the XMM-Newton satellite. I demonstrate this method using 32 observations of M31 by fitting the OVIII Ly-alpha and OVII K-alpha transitions. I show that the observed spectral peculiarities are much more likely the result of resonance scattering, rather than SMBH feedback effects seen through plasma overionization. A semiparametric extention of that work is also provided in an appendix. Finally, I conclude with a discussion of the usefulness of spatio-spectral analysis and highlight the promising research toward understanding galactic feedback that can be done as an extention to the work herein.Publication Intrinsic Characteristics of Galaxies in the Distant Universe: The Correlation Between Galaxy Morphology and Star Formation Activity(2017) Lee, BomeeOne of the major questions in observational cosmology is how galaxies formed and how they evolved. In particular, understanding the assembly history of galaxies at the peak epoch of the star formation activity, z=1-3, is a key to understanding the whole picture of the Universe, but remains uncertain. Galaxies with various physical properties and morphologies have different formation and evolution histories. As such, we seek insight into galaxy formation and evolution at z=1-3 using galaxies selected from Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) in this dissertation. First, we investigate the relationship between spectral types and morphologies using various parametric diagnostics and visual inspections. Our sample clearly separates into massive, red, and passive galaxies versus less massive, blue, and star forming ones, and this dichotomy correlates very well with the galaxies' morphological properties. From this study, we suggest that the backbone of the Hubble sequence was already in place at z~2. Second, we explore how the choice of star formation histories affects estimating galaxy properties by adopting flexible star formation history models to the fitting of galaxy's spectrum. The estimation of galaxy properties is improved using CANDELS observations providing unprecedented coverage and depths, and using an advanced fitting technique. We find that galaxy properties, particularly age and star formation rate, are sensitive to the choice of star formation histories. We also find that using different best-fit star formation histories leads to significantly different results on the main sequence of star formation. Our results demonstrate that using the best-fit star formation history for each galaxy is more appropriate way than using one analytic model for all galaxy types. Third, with accurately measured stellar mass and star formation rate, we study characteristics of galaxies on, above, and below the main sequence. We find that distinct morphological differences are shown among different galaxy populations using various diagnostics. On average, as star formation activities decrease, galaxies become denser having smaller sizes and steeper light profiles at all explored redshifts. We also show that the compact morphology is not necessary to precede a passivity of star formation. Our results do not support that gas-rich merging is the key driver to assemble very compact, massive early-type galaxies observed at z~2. Instead, we suggest that compact galaxies simply assemble at very early times and evolve through in situ star formation to form compact massive, quiescent galaxies without significant merging events.Publication The Cosmic Web, and the Role of Environment in Galaxy Evolution(2016-09) Cybulski, RyanThe Universe, on extra-galactic scales, is composed of a vast network of structures dubbed the “cosmic web”. One of the most fundamental discoveries about the evolution of galaxies is that their properties have a dependence on their location relative to this cosmic web (i.e., their environment). However, detailed studies of the environmental dependence on galaxy evolution have been extremely challenging due to the inherent complexity of the structures on the largest scales, a plethora of techniques being used to try to map the cosmic web, and other confounding factors, such as the masses of galaxies, that also affect their evolution. In this work, we will present a technique for characterizing the environments of galaxies in the cosmic web, which is comprised of two separate, but complementary, methods that together provide a more complete measure of environment. After some introductory background in Chapter 1, we will demonstrate these mapping techniques on the Coma Supercluster, and present an analysis of the star-formation activity of about 4,000 galaxies in the supercluster environment in Chapter 2. Next, in Chapter 3 we present a greatly expanded application of our mapping techniques encompassing about 60,000 galaxies within 200 Mpc that addresses several outstanding questions from the Coma Supercluster study, and also leads to new intriguing insights into the evolution of galaxies as a function of environment. Then, in Chapter 4 we present a pilot study focusing on galaxy evolution as traced by the gas content around two galaxy clusters. We also expand upon this pilot study in Chapter 5, whereupon we examine more closely the resiliency of molecular gas content, compared to the atomic gas, to the effects of the cluster environment. And finally, in Chapter 6 we present some concluding remarks and explore some promising avenues for future study.Publication The Effect of a Growing Black Hole on the Infrared Emission of Dusty Galaxies in the Distant Universe(2016-05) Kirkpatrick, AllisonThe buildup of stellar and black hole mass peaked during z=1-3. Infrared (IR) luminous galaxies, which are massive and heavily dust obscured (LIR > 1011 Lsun), dominate the stellar growth during this era, and many are harboring a hidden active galactic nucleus (AGN). We have quantified the contribution of AGN heating to the infrared emission of a large sample of dusty, luminous galaxies from z=0.5-4 using Spitzer mid-IR spectroscopy, available for every source. We classify sources as star forming galaxies, AGN, or composites based on the presence of mid-IR continuum emission due to a dusty torus. 60% of our sample shows signs of some dust heating emanating from an AGN, and that an AGN is clearly linked with increasing dust temperatures. We quantify the far-IR emission using deep Herschel imaging and find that the strength of mid-IR AGN emission is tightly correlated with the total contribution of an AGN to LIR, which has important consequences for calculating star formation rates in dusty high redshift galaxies. We calibrate techniques to remove the contribution of AGN to LIR. Because of dust obscuration, much of this AGN activity is undetected at other wavelengths, but we present new color diagnostics to effectively identify heavily obscured AGN. We discuss the role that mergers might play in fueling AGN growth and find our galaxies to be generally consistent with the picture that a major merger triggers an AGN. We test what effect an IR luminous AGN has on the star formation efficiency (the star formation rate compared with the molecular gas mass) using a pilot sample of 24 galaxies at zPublication An empirical approach to understanding of star formation in dark matter halos(2015-09) Lu, ZhankuiWe present a data-driven approach to understand the star formation in dark matter halos over cosmic time. With a simple empirical model and advanced tools for Bayesian inference, we try to constrain how galaxies have assembled their stars across cosmic time using stellar mass functions (SMFs) and the luminosity function of cluster galaxies. The key ingredients of the empirical model include dark halo merger trees and a generic function that links star formation rate (SFR) to the host halos. We found a new characteristic redshift zc ~ 2 above which the SFR in low mass halos < 1011 solar mass must be enhanced relative to that at lower z. This leads to some interesting predictions, for instance, a signicant old stellar population in present-day dwarf galaxies with mass of 108 solar mass and steep low-mass end slopes of high redshift SMFs. The constrained empirical model can be combined with other other observational constraints to infer the physics behind the evolution of galaxies. The classical bulge mass could be derived from the major mergers of the host galaxies. Applying the central black hole (BHs) - classical bulge relation, it predicts all galaxies with stellar mass less than 1010.5 solar mass host intermediate mass BHs (MBH < 107solar mass). Using the gas phase metallicity we study the evolution of gas and metal content of star forming galaxies and the infow and outfow rates. About 60% of the metals produced have been lost. At low redshift (z < 1) the accretion of pristine gas should be lower by a factor of few than expected and the loading factor of gas outfow that is not recycled is of order of unity. The empirical model also serves as basis to study the evolution of satellite galaxies. The progenitors of present-day satellites can be initialized using this empirical model. The physically motivated models of quenching of star formation in satellites, including strangulation, ram pressure stripping of cold gas disks, and tidally triggered starburst, are tested against statistics of the group catalogs.Publication TolTEC: A New Multichroic Imaging Polarimeter for the Large Millimeter Telescope(2024-02) DeNigris, Nat SThe TolTEC camera is a new millimeter-wave imaging polarimeter designed to fill the focal plane of the 50-m diameter Large Millimeter Telescope (LMT). Combined with the LMT, TolTEC offers high angular resolution (5", 6.3", 9.5") for simultaneous, polarization-sensitive observations in its three wavelength bands: 1.1, 1.4, and 2.0 mm. Additionally, TolTEC is designed to reach groundbreaking mapping speeds in excess of 1 deg2/mJy2/hr, which will enable the completion of deep surveys of large-scale structure, galaxy evolution, and star formation that are currently limited when considering practical observation times for other ground-based observatories. This thesis covers the design as well as the in-lab and LMT characterization of the instrument. Chapter 2 covers TolTEC's design overview and describes each subsystem (cryogenics, optics, detectors, and detector readout). Chapter 3 examines the performance of each subsystem prior to installation at the LMT. In particular, this chapter provides the instrument's responsivity, efficiency, beam response, and readout noise while testing at UMass Amherst. The following chapter covers the initial results from commissioning at the LMT between December 2022 and April 2023. Based on the in-lab testing and LMT commissioning, I provide a number of procedures for operating/repairing the instrument in the appendices. I conclude Chapter 5 with the development of a new pilot study to leverage TolTEC's high resolution and sensitivity with the goal of exploring galaxy cluster thermodynamics across cosmic time. While TolTEC observations of galaxy clusters were not available for this thesis, I describe the analysis pipeline I developed to perform a power spectrum analysis on intracluster medium (ICM) pressure fluctuations. The result of this pipeline is a power spectrum that can be analyzed to extract information on the thermodynamic state of the ICM. This type of study has only been performed on two clusters as of 2023, thus with TolTEC's mapping speed and sensitivity we will be able to expand this study and create the largest sample of its kind.Publication Probing the Physical Mechanisms Responsible for Brown Dwarf and Giant Planet Formation(2023-09) Betti, SarahThe disks that form around young stellar objects provide the essential material for their continued growth as well as the formation of planets, making them ideal laboratories to investigate the mechanisms and environments key for substellar and planetary formation. In this dissertation, I explore two main formation processes: the transportation of water necessary for giant planet formation, and the accretion and growth of young brown dwarfs. First, I study the water ice content in the circumstellar disk of AB Aurigae, a young Herbig Ae star. I detect and map icy grains on the disk surface using high contrast observations taken with LMIRCam on the LBTI. I find that within < 200 au from the central star, far closer than expected, the surface is composed of grains that are approximately 5% ice by mass. This indicates there is either strong vertical mixing or the scattering surface is shielded from photodesorption, allowing these grains to survive. In the second part of this dissertation, I investigate the mechanisms responsible for accretion and formation of protoplanets and brown dwarfs. I detect, for the first time in a protoplanet, NIR emission from Delorme 1 (AB)b, and find its line emission appears to originate from shocks at the planet surface. To determine how accretion mechanisms vary between protoplanets, brown dwarfs, and low mass T Tauri stars, I compile the most complete, to date, database of published accretion rates of these objects (Comprehensive Archive of Substellar and Planetary Accretion Rates; CASPAR). From CASPAR, I show that the scatter in accretion rate at different stellar masses is best explained by a combination of the systematic (i.e. choice of model) scatter in surveys as well as the mass and age of the systems, with the rate of accretion steepening with age in the substellar regime. However, I also find that accretion rates derived from different tracers begin to diverge within the substellar mass regime when utilizing stellar empirical relationships between accretion and line luminosities. I then introduce initial work to investigate this divergence between continuum and line luminosity derived accretion rates through a survey of mass accretion in brown dwarfs using near infrared (NIR) accretion tracers. I create new empirical relationships between NIR hydrogen line luminosity and total accretion luminosity for brown dwarfs, and find that these revised relations resolve the offset in tracers shown in CASPAR. I show that material is infalling from accretion columns at low free fall velocities for BDs, indicating that, unlike stars, the emission could originate from the column or at the BD surface.Publication The coeval mass assembly of the universe via supermassive black hole accretion and star formation in galaxies(2023-02) Sokol, AlyssaThe possible co-evolution between galaxies and their central supermassive black holes is supported by the similarity in shape between the Star Formation Rate Density (SFRD) and Black Hole Accretion Rate Density (BHARD) out to z$\sim$ 3. This apparent connection between BH growth and star formation is only established globally; while both trends peak at z$\sim$ 2, the amount of stellar and black hole mass assembly occurring within the same galaxies is unknown. Computing these trends for the same galaxies will mitigate the present sample mismatch and can be accomplished with an IR-selected sample; however, the approach relies on a robust understanding of broadband UV-FIR SED fitting to reliably decompose AGN and SF luminosities over a range of AGN strengths. UV-FIR SED fitting is an effective way to disentangle emission between star formation (SF) and active galactic nuclei (AGN) in galaxies with sufficient broadband photometry. The precision of this approach, however, is affected by the sparse mid-IR data presently available in statistically large samples and the variety of AGN SED shapes predicted by radiative transfer torus models. Given these constraints, the use of SED fitting to characterize supermassive black hole accretion is more uncertain in composite AGN/SF galaxies, when the mid-IR SED is \textit{not} overwhelmed by AGN emission. This is significant, as composite galaxies are ubiquitous in nature ($\sim$ 50-70\% of IR-selected samples) and may represent either weak, low-luminosity AGN or a more luminous AGN population that is heavily dust obscured. In this thesis we construct the SFRD and BHARD for the same sample of galaxies, selected at 250$\mu$m in the COSMOS field, testing a variety of AGN SED decomposition methods and AGN templates. We find that employing optically thick AGN torus models results in a BHARD that is higher than current X-ray observations predict but is more similar to the Compton-Thick BHARD predicted by X-ray population synthesis models. This large population of luminous obscured AGN, revealed by SED Decomposition, results in a BHARD trend that drops more rapidly with decreasing redshift than the corresponding SFRD. Our results imply that universal mass assembly via SMBH growth and SF are not directly linked to grow their mass at similar rates across similar epochs.