Astronomy
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Item Case Studies in AGN Feedback(2022) Smith, Robyn N; Reynolds, Christopher S; Veilleux, Sylvain; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Galaxies in which the central supermassive black hole (SMBH) is actively accreting are referred to as active galactic nuclei (AGN) and are believed to play a crucial role in the evolution of both individual and clusters of galaxies. Empirically, the mass of the host galaxy and the mass of the SMBH are positively correlated. This is somewhat surprising given that the gravitational sphere of influence of the SMBH is orders or magnitude smaller than the host galaxy. The SMBH is believed to undergo periods of activity during which it is capable of powering galactic-scale outflows which in turn modulate star formation and therefore the overall mass of the host galaxy. Such processes are broadly referred to as feedback.Clusters of galaxies are the largest gravitationally bound systems in the universe. The intracluster medium (ICM) in relaxed clusters is strongly centrally peaked and suffi- ciently dense that it is expected to cool rapidly (in cosmological terms). Such cooling should create streams of cool gas flowing to the brightest cluster galaxy (BCG) which in turn should fuel high rates of star formation. Little evidence of either has been found giving rise to the ‘cooling flow problem’. AGN are again invoked to explain the absence of this cooling flow. The BCGs hosting AGN, often with powerful radio jets, are believed to inject energy into the ICM at a rate which can counteract the cooling. This cyclical nature of balancing the cooling is another form of AGN feedback. In this thesis, we present case studies of three AGN which provide unique insight into these feedback processes. Chapter 2 presents evidence for a relativistic X-ray driven outflow on accretion disk scales in an ultraluminous infrared galaxy known to host a galactic-scale molecular outflow. The observational properties which make a galaxy an ideal candidate for detection of large-scale outflows are intrinsically at odd with the properties which are ideal for detecting small-scale outflows. IRASF05189-2524, the subject of Chapter 2, is one of only a handful of galaxies for which positive detection of outflows on both small- and large-scale exist. Next, we turn our attention to AGN in BCGs and the cooling flow problem. Chapter 3 presents new Chandra observations of NGC 1275, the BCG in the famous Perseus Cluster. The high-cadence observing campaign finds X-ray variability on short intraweek timescales. The inclusion of archival observations reveals a general ‘harder when brighter’ trend. Examination of multiwavelength light curves finds a strongly correlated optical and γ-ray flare in late 2015 in which the optical emission leads the γ-ray emission by ~5 days. This robust (> 3σ) result is the first strong evidence of correlated emission with a time delay and is lends support to the idea that the γ-ray emission is produced by synchrotron self-Compton upscattering. In Chapter 4, we present new Chandra observations of the rare radio-quiet BCG quasar H1821+643. It is one of only two examples in the nearby universe of a highly luminous quasar with minimal radio jet activity at the center of a galaxy cluster. Despite observational challenges, we produce the first high-resolution spectrum of the quasar well-separated from the ICM in ~20 years. Our short-cadence observing campaign again reveals rapid variation on timescales corresponding to the light crossing time of the accretion disk. Although the flux varies, the spectrum is remarkably constant when compared to observations from previous decades. The result of this thesis is to add to the existing body of knowledge of AGN feedback on both galaxy and galaxy cluster scales. These three AGN presented various observing challenges which required a combination of non-standard observational techniques and data reduction methods in order to maximize results with current X-ray instrumentation.Item Investigating Star Formation Feedback Through Gas Kinematics in Nearby Galaxies(2021) Levy, Rebecca Chyba; Bolatto, Alberto D; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many stages of the stellar life cycle release energy and momentum into the surrounding interstellar medium within a galaxy. This feedback can have profound effects on the host galaxy. This thesis investigates the role of stellar feedback in star-forming galaxies in the local Universe through multiwavelength observations of gas kinematics. First, I study extraplanar diffuse ionized gas (eDIG) which is thought to be produced by gas ejected from the midplane by repeated supernova explosions. By comparing molecular and ionized gas rotation curves derived from a sub-sample of intermediate inclination star-forming galaxies from the EDGE-CALIFA Survey, I find that ~75% of my sample galaxies have smaller ionized gas rotation velocities than the molecular gas. I suggest and show that the lower ionized gas rotation velocity can be attributed to a significant contribution from eDIG in a thick disk which rotates more slowly than gas in the midplane. As a direct follow up to this study, I use a sample of edge-on galaxies selected from the CALIFA survey to directly investigate the prevalence, properties, and kinematics of eDIG. I find that 60% of these galaxies show a decrease in the ionized gas rotation velocity as a function of height above the midplane. The ionization of the eDIG is dominated by star-forming complexes. These studies reveal the pervasiveness and importance of this phase in local star-forming galaxies. Next, I study stellar feedback in the extreme environment of the nuclear starburst in the nearby galaxy NGC 253. Using ALMA observations with 0.5 pc resolution, I detect blueshifted absorption and redshifted emission (P-Cygni profiles) in multiple spectral lines towards three of the super star clusters (SSCs). This is direct evidence for outflows of dense molecular gas from these SSCs. Through a comparison of the outflow properties with predictions from simulations, I find that the outflows are most likely powered by dust-reprocessed radiation pressure or O-star stellar winds. The observed outflows will have very substantial effects on the clusters' evolution. Finally, I find that the arrangement of the SSCs may be morpho-kinematically consistent with a ring or crossing streams from the larger-scale gas flows which fuel the starburst.Item From Tantrums to Transformations: AGN Transients Discovered with the Zwicky Transient Facility(2021) Frederick, Sara; Gezari, Suvi; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation work has consisted of searches for extreme AGN-related outbursts during Phase I of the Zwicky Transient Facility (ZTF) survey, which has been a ground-breaking wide-field instrument for the real-time detection and regular cadence monitoring of transients in the Northern Sky. Transients found to be nuclear through photometric filtering were vetted by humans and coordinated for prompt follow-up with various rapid robotic, spectroscopic, and high energy resources, to understand the nature of the galaxy centers undergoing flares and the appearance of spectral features. Findings from this unprecedentedly high-volume data stream were often serendipitous, and led to surprising new avenues for study, including 1) the establishment of a new observational class of quiescent galaxies caught turning into quasars, 2) the discovery of a preponderance of smooth and high-amplitude optical transients hosted in NLSy1s, and 3) a framework for distinguishing extreme AGN variability from other transients in AGN. We present the results of these observations, including candidates for TDEs in AGN, changing-look AGN caught "turning-on", as well as members of the new emerging observational class of flares in Narrow-Line Seyfert 1 (NLSy1) galaxies associated with enhanced accretion (Trakhtenbrot et al. 2019). We compared the properties of these samples of flares to previously reported changing-look quasars and Seyfert galaxies, confirmed that they are a unique observational class of transients related to physical processes associated with the central supermassive black hole's accretion state, and considered the observations in the context of the physical interpretations for a range of related transients from the literature. With these unique sample sets, we also aim to understand why we have found certain galaxy types to preferentially host the sites of such rapid enhanced flaring activity, and attempt to map out the innermost environment of the accretion events. These pathfinding studies enabled with ZTF have the potential to guide how these exceptional moments of AGN evolution will be systematically discovered in future large area surveys such as the Vera C. Rubin Observatory.Item Gas and Star Formation at the Peak of Cosmic Star Forming Activity(2021) Lenkic, Laura; Bolatto, Alberto; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Gas and star formation in galaxies are intimately linked to one another. Molecular hydrogen gas is the material out of which stars form, while the process of forming stars, in turn, depletes the reservoirs of gas in galaxies and builds up their stellar mass. Observations of star formation in galaxies over time indicate that they must form stars for timescales longer than would be expected from their gas content and star formation rates, indicating that processes that replenish the star forming fuel must be present. The focus of this thesis is on two components of this qualitative picture: the molecular hydrogen gas content of galaxies over time, and the link between gas and star formation in galaxies resembling those observed at the epoch of most active star formation. First, I present a systematic search for serendipitous carbon monoxide emitting sources in the second Plateau de Bure High-z Blue-Sequence Survey (PHIBSS2). These observations presented an opportunity to quantify the mass density of molecular gas in galaxies as a function of time, and to link this to the star formation history of the Universe. I use a match-filter technique to systematically detect 67 serendipitous sources, after which I characterize their properties, creating a catalog of their redshifts, line widths, fluxes, estimations of the detection reliability, and completeness of the detection algorithm. I find that these serendipitous sources are unrelated to the primary sources that were targeted by PHIBSS2, and use the catalog to construct luminosity functions spanning a redshift range from $\sim 0.3-5$. From these luminosity functions, I place constraints on the molecular hydrogen content in galaxies over cosmic time. My work presents one of the first attempts to use existing observations for this measurement and yields results that are consistent with previous studies, while demonstrating the scientific power of large, targeted surveys. Next, I study a sample of rare, nearby galaxies that are most similar to those we observe at the peak of cosmic star forming activity that occured $\sim 10$ billion years ago. These galaxies are drawn from the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey, and their proximity to us allows for very detailed studies of their massive star forming clumps. I use observations from the Hubble Space Telescope (HST) to measure colors that are sensitive to stellar population age and extinction. From these measurements, I find that clumps in DYNAMO galaxies have colors that are most consistent with very young centers and outskirts that appear systematically older, by as much as 150~Myr in some cases. I attribute this age difference to the presence of ongoing star formation in the centers of clumps that maintains the population of massive, short-lived stars and gives rise to colors consistent with young ages. Furthermore, I find that within the disks of their host galaxies, younger clumps are preferentially located far from galaxy centers, while older clumps are preferentially located closer to the centers. These results are consistent with hydrodynamic simulations of high-redshift clumpy galaxies that predict clumps form in the outskirts of galaxies via a violent disk instability, and as they age, migrate to the centers of galaxies where they merge and contribute to the growth of galactic bulges. Building on this study, I combine observations of DYNAMO galaxies from the HST and the Atacama Large Millimeter/sub-millimeter Array (ALMA) to trace molecular hydrogen gas and star formation. I link these observations to measurements of the molecular gas velocity dispersions to test theories of star formation. I find that compared to local samples of ``normal'' star forming galaxies, DYNAMO systems have consistently high velocity dispersions, molecular gas surface densities, and star formation rate surface densities. Indeed, throughout their disks, DYNAMO galaxies are comparable to the centers of local star forming galaxies. Stellar bar driven gas flows into the centers of galaxies in these local samples may give rise to the high observed velocity dispersions, and gas and star formation rate surface densities. For DYNAMO galaxies, the widespread elevated values of these parameters may be driven by galactic-scale gas inflows, which is predicted by theories. Finally, current theories of star formation, such as the feedback regulated model, assume that turbulence dissipates on timescales proportional to the angular velocity of a galaxy (eddy or crossing time). Yet, I find such models have difficulty reproducing the DYNAMO measurements, and thus conclude that the turbulent dissipation timescale in DYNAMO galaxies must scale with galactocentric radius.Item Gamma-ray Bursts: Lighting up the High-Redshift Universe(2017) Toy, Vicki; Veilleux, Sylvain; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Gamma-ray bursts (GRBs) are the most luminous events in the Universe with Eγ,iso ∼ 10^48−54 erg. Leading models hypothesize that GRBs are created from inter- nal collisions within collimated and ultrarelativistic jets. The jets then shock-heat the surrounding material (e.g. interstellar medium) to create GRB afterglows. These afterglows are extremely useful probes of the Universe because long GRBs are (1) bright events that can be used as backlights for absorption studies, (2) able to probe at all redshifts massive stars exist, and (3) transient events that allow us to follow- up on the host galaxies at late times. In this thesis we study the environments of GRBs. We first explore the relationship between GRB and supernova (SN) using a nearby GRB-SN (GRB 130702A/SN 2013dx) at z = 0.145. There are only nine other GRB-SNe that were close enough to have extensive spectroscopic and photometric follow-up of the SN at late times. We create a quasi-bolometic light curve of SN 2013dx and fit an analytical equation to the quasi-bolometric light curve combined with measurements of the photospheric velocity to determine SN parameters: mass of 56Ni, kinetic energy, and ejecta mass. We examine the relationship between SN parameters and Eγ,iso for the 10 well-studied GRB-SNe, but find no correlations despite numerical simulation predictions that the mass of 56Ni should correlate with the degree of asymmetry. We then move to larger distance scales and use GRB afterglows as bright back- lights to study distant galaxies. We examine the galactic environments of Damped Lyman-α systems (DLAs; NHI ≥ 10^20.3 cm^−2 ) identified with GRB afterglows at z ∼ 2 − 6. We use late-time photometry after the GRB afterglow has faded to determine star formation rates (SFRs) from rest-frame ultraviolet measurements or spectral energy distribution (SED) models from multiband photometry. We com- pare our sample’s SFRs to a sample of quasars (QSOs) DLA host galaxies. Despite the overlapping NHI and redshift ranges, our GRB-DLA galaxies have much larger SFRs than the QSO-DLA host galaxy sample; this may suggest that the QSO-DLA and GRB-DLA galaxy populations are different. We also compare star formation efficiencies to the local Universe and simulations at z = 3. A large portion of this thesis has focused on the development of a new ground- based GRB afterglow follow-up instrument, the Rapid infrared IMAger-Spectrometer (RIMAS), that will target high-redshift GRB afterglows to study early galaxy envi- ronments. RIMAS covers 0.97-2.37 μm and can simultaneously observe two band- passes in any observing mode: photometry, low-resolution spectroscopy (R ∼ 30), or high-resolution spectroscopy (R ∼ 4000). In particular, this thesis focuses on RIMAS’s three detectors: two science grade Teledyne HgCdTe Astronomy Wide Area Infrared Imager with 2K x 2K, Reference Pixels and Guide Mode (H2RG) and a slit-viewer Spitzer Legacy Indium-Antimonide (InSb) array. We describe the detector hardware and characterization in detail and discuss general infrared detector troubleshooting methods at both cryogenic and room temperatures. Several software packages have been developed for RIMAS throughout this thesis work. We introduce RIMAS’s quick reduction pipeline that takes raw images from a single acquisition and returns a single result frame. We then present a generalized data reduction pipeline that we have tested on two currently operational photometers. We also describe our detailed and realistic RIMAS throughput models for all three observing modes as well as our online observer calculators with these throughput models. All of our data products are open source and are publicly available on Github repositories with detailed documentation.Item The Star-Forming Properties of an Ultra-Hard X-ray Selected Sample of AGN(2016) Shimizu, Thomas Taro; Mushotzky, Richard; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis provides a comprehensive examination of star formation in the host galaxies of active galactic nuclei or AGN. AGN are bright, central regions of galaxies that are powered through accretion onto a supermassive black hole (SMBH). Through accretion and the loss of gravitational potential energy, AGN emit powerful radiation over all wavelengths of the electromagnetic spectrum. This radiation can influence the AGN's host galaxy through what is known as AGN ``feedback'' and is thought to suppress star formation as well as stop accretion onto the SMBH leading to a co-evolution between the SMBH and its host galaxy. Theoretical models have long invoked AGN feedback to be able reproduce the galaxy population we see today but observations have been unclear as to whether AGN actually have an effect on star formation. To address this question, we selected a large sample of local ($z < 0.05$) AGN based on their detection at ultra-hard X-ray energies (14--195 keV) with the \textit{Swift} Burst Alert Telescope (BAT). Ultra-hard X-ray selection frees our sample from selection effects and biases due to obscuration and host galaxy contamination that can hinder other AGN samples. With these 313 BAT AGN we conducted a far-infrared survey using the \herschel \textit{Space Observatory}. We use the far-infrared imaging to probe the cold dust that traces recent star formation in the galaxy and construct spectral energy distributions (SEDs) from 12--500 \micron. We decompose the SEDs to remove the AGN contribution and measure infrared luminosity which provides us with robust estimates of the star formation rate (SFR). Through a comparison with a stellar-mass matched non-AGN sample, we find that AGN host galaxies have larger dust masses, dust temperatures, and SFRs, confirming the results of previous studies that showed the optical colors of the BAT AGN are bluer than non-AGN. We find that the AGN luminosity as probed by the 14--195 keV luminosity is not related to the SFR of the host galaxy suggesting global, large scale star formation on an individual basis is not affected by the AGN. However, after a thorough analysis comparing our AGN to star-forming main sequence, a tight relationship between the SFR and stellar mass of a galaxy, we discover that our AGN as a whole show systematically lower specific SFRs (SFR/stellar mass). We confirm that AGN host galaxies, as a population, are transitioning between the star-forming and quiescent populations. This result supports the theory that AGN feedback has suppressed star formation, but we also consider other models that could reproduce our observations. Finally we conclude with a summary of this thesis and describe several ongoing and future projects that will push forward the exciting field of AGN research.Item Dust and Molecular Gas in the Winds of Nearby Galaxies(2015) McCormick, Alexander; Veilleux, Sylvain; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Galactic winds provide a fundamental mechanism for galaxy evolution. The outflow of material in winds remains the most likely culprit responsible for a host of galaxy observations, plus mounting evidence for galactic winds at times in the past points to their importance in understanding the history of the universe. Therefore, detailed observations of galactic winds are critical to fleshing out the narrative of galaxy evolution. In particular, the dust and molecular gas of a galaxy's interstellar medium (ISM) play crucial roles in the absorption, scattering, and reemission of starlight, the heating of the ISM, and provide critical materials for star formation. We present results from archival {\em Spitzer Space Telescope} data and exceptionally deep {\em Herschel Space Observatory} data of the dust and molecular gas found in and around 20 nearby galaxies known to host galactic-scale winds. Selecting nearby galaxies has allowed us the resolution and sensitivity to differentiate dust and molecular gas outside the galaxies and observe their typically faint emission. These are the most detailed surveys currently available of the faint dust and molecular gas components in galactic winds, and we have utilized them to address the following questions: i) What are the location and morphology of dust and molecular gas, and how do these components compare with better known neutral and ionized gas features? ii) How much do dust and molecular gas contribute to the mass and energy of galactic winds? iii) Do the properties of the dust and molecular gas correlate with the properties of the wind-hosting galaxy? {\em Spitzer} archival data has revealed kiloparsec-scale polycyclic aromatic hydrocarbon (PAH) structures in the extraplanar regions of nearly all the wind-hosting galaxies we investigated. We found a nearly linear correlation between the extraplanar PAH emission and the total infrared flux, a proxy for star formation. Our results also suggest a correlation between the height of extraplanar PAH emission and star formation rate surface density, supporting the idea of a surface density threshold on the energy or momentum injection rate for producing detectable extraplanar wind material. New, very deep {\em Herschel} data of six nearby dwarf galaxies with known winds show circumgalactic cold dust features on galactic scales, often well beyond the stellar component. Comparisons of these features with ancillary data show an imperfect spatial correlation with the ionized gas and warm dust wind components. We found $\sim$10-20\% of the total dust mass in these known wind galaxies resides outside their stellar disks, and $\sim$70\% in one case. Our data also hint at metallicity depletion via cold dust ejection and possible correlations of dust and other host galaxy properties, though these tantalizing implications are not statistically significant given the small number of objects in the sample and the uncertainties in the measurements.Item Two Dimensional Velocity Fields of Low Surface Brightness Galaxies(EDP Sciences, 2005) Kuzio de Naray, R.; McGaugh, S. S.; de Blok, W. J. G.; Bosma, A.We present high resolution two dimensional velocity fields from integral field spectroscopy along with derived rotation curves for nine low surface brightness galaxies. This is a positive step forward in terms of both data quality and number of objects studied. We fit NFW and pseudo-isothermal halo models to the observations. We find that the pseudo-isothermal halo better represents the data in most cases than the NFW halo, as the resulting concentrations are lower than would be expected for CDM.Item A Catalog of Low Surface Brightness Galaxies: List II(Copyright American Astronomical Society, 1992-04) SCHOMBERT, JAMES M.; BOTHUN, GREGORY D.; SCHNEIDER, STEPHEN E.; MCGAUGH, STACY S.Item Star Formation Thresholds in Low Surface Brightness Galaxies(Copyright: American Astronomical Society, 1993-08) VAN DER HULST, J. M.; SKILLMAN, E. D.; SMITH, T. R.; BOTHUN, G. D.; MCGAUGH, S. S.; DE BLOK, W. J. G.