BA, Oberlin College, 2022, Physics and Astronomy

In this thesis, I introduce a method to identify and characterize the effects of active galactic nuclei (AGN) on the spectra of nearby star-forming regions. I analyze spatially-resolved areas of galaxies called “spaxels” within Data Release 15 of the Sloan Digital Sky Survey (SDSS) with the goal of locating those which are physically close to AGN. I find those spaxels with calculated metallicities which lie adjacent to AGN-flagged spaxels and characterize their metallicity values relative to the spaxels which are not adjacent to AGN-flagged spaxels, using a total of 11 separate metallicity calibrations. I find that the current methods to mask AGN-influenced regions for large-scale investigation are, in general, robust, as the largest median deviation between metallicities in border spaxels and those in non-border spaxels is 0.0467 dex. The largest mean difference in metallicity between border and non-border spaxels is 0.0522 dex with a standard deviation of 0.0590 dex. However, on a spaxel-by spaxel basis, I find that the differences in metallicity between border spaxels and non-border spaxels can be as large as 0.9350 dex. These results are concerning for spaxel-by-spaxel analysis, and indicate the need for an improved masking process in the future.

Committee: Jillian Scudder (Advisor) Subjects: Astronomy; Astrophysics; Physics

Doctor of Philosophy (PhD), Ohio University, 2019, Physics and Astronomy (Arts and Sciences)

This dissertation consists of two parts. In the first part, we focus on studying the nuclear outbursts in the centers of galaxies and their nature in order to better understand the behavior of central Super Massive Black Holes (SMBHs) and their interaction with the surrounding environment, and to better understand the accretion disk structure. Nuclear outbursts can be better understood by studying the changes in the broad emission lines and the underlying continuum. We quantify the properties of these nuclear outbursts using multi-wavelength observations including optical, ultraviolet, and X-rays from MDM Observatory, the Sloan Digital Sky Survey, Swift, and Magellan. Some of these nuclear outbursts are linked to Tidal Disruption Events (TDEs) and nuclear supernovae (SNs), while a number of these events are proposed to be a rare phenomenon called “changing-look” Active Galactic Nuclei (AGN). These types of AGNs have been observed to optically transition from type 1 to type 2 and vice versa on timescales of months to years, where broad emission lines such as Hα and Hβ appeared or disappeared followed by an increase or decrease in the continuum light. We investigate two transient events called PS1-13cbe and PS1-10cdq that were observed during outburst by the PS1 survey in 2013 and 2010, respectively. We investigate TDE, SN, and AGN activity as the three possible scenarios for the nature of these events. In the case of PS1- 3cbe, we conclude that “changing-look” behavior caused by thermal accretion disk instabilities is the most plausible explanation for the outburst. However, in the case of PS1-10cdq, we favor the tidal disruption scenario because of the structure of the lightcurve and spectral evolution. In the second part of this dissertation, we focus on galaxy morphology prediction using a newly designed neural network called “Capsule Networks”. We automate the process of morphology prediction and eliminate the need for feature engineering and heavy data preposses (open full item for complete abstract)

Committee: Ryan Chornock Dr (Advisor); Prakash Madappa Dr (Committee Member); Shields Joseph Dr (Committee Member); Bunescu Razvan Dr (Committee Member) Subjects: Astronomy; Astrophysics; Physics

Doctor of Philosophy (PhD), Ohio University, 2016, Physics and Astronomy (Arts and Sciences)

This dissertation focuses on placing observational constraints on outflows and accretion disks in active galactic nuclei (AGN) for the purpose of better understanding the physics of super-massive black holes (SMBHs) and their evolution with the host galaxy over cosmic time. Quasar outflows and their importance in SMBH–host galaxy co-evolution can be further understood by analyzing broad absorption lines (BALs) in rest-frame UV spectra that trace a range of wind conditions. We quantify the properties of the flows by conducting BAL variability studies using multiple-epoch spectra acquired primarily from MDM Observatory and from the Sloan Digital Sky Survey. Iron low-ionization BALs (FeLoBALs) are a rare type of outflow that may represent a transient phase in galaxy evolution, and we analyze the variations in 12 FeLoBAL quasars with redshifts between 0.7 < z < 1.9 and rest frame timescales between 10 d to 7.6 yr. We investigate BAL variability in 71 quasar outflows that exhibit P V absorption, a tracer of high column density gas (i.e. NH > 1022 cm-2), in order to quantify the energies and momenta of the flows. We also characterize the variability patterns of 26 quasars with mini-BALs, an interesting class of absorbers that may represent a distinct phase in the evolution of outflows. Low-luminosity AGN (LLAGN) are important objects to study since their prominence in the local Universe suggest a possible evolution from the quasar era, and their low radiative outputs likely indicate a distinct mode of accretion onto the SMBH. We probe the accretion conditions in the LLAGN NGC 4203 by estimating the SMBH mass, which is obtained by modeling the 2-dimensional velocity field of the nebular gas using spectra from the Hubble Space Telescope. We detect significant BAL and mini-BAL variability in a subset of quasars from each of our samples, with measured rest-frame variability time-scales from days to years and over multiple years on average. Variable wavelength intervals a (open full item for complete abstract)

Committee: Joseph Shields (Advisor); Douglas Clowe (Committee Member); Douglas Green (Committee Member); Madappa Prakash (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy (PhD), Ohio University, 2015, Physics and Astronomy (Arts and Sciences)

Blazars are one kind of radio-loud Active Galactic Nuclei whose jets are directed close to our line of sight. They have characteristic two-hump shaped spectral-energy-distributions, strong variability across the entire electromagnetic spectrum, and high polarization degrees with variations from radio to optical. This dissertation presents a detailed study on the polarization signatures in blazar emission. At high energies (X-ray to γ-ray), we present theoretical estimates for the maximal polarization degrees resulting from both the leptonic and hadronic models, in which we find that the polarization signatures can serve as a powerful diagnostic between the two models. At low energies (radio to optical), we present a general parameter study on the time- and frequency-dependent polarization signatures along with the multiwavelength spectra and variability. Based on our results, we present the first simultaneous fittings of the snap-shot spectral-energy-distributions, multiwavelength light curves and time-dependent polarization signatures in one coherent model of a prominent blazar flaring event that is accompanied by a drastic change in the polarization signatures. This unprecedented fitting combination provides crucial information about the inner-jet magnetic field topology, particle acceleration and radiation mechanisms giving rise to the observed blazar emission.

Committee: Markus Boettcher (Advisor) Subjects: Astrophysics

Doctor of Philosophy, The Ohio State University, 2011, Astronomy

I present the results of a mid-infrared (MIR) survey of X-ray point sources in 8 low-z galaxy clusters. I combine visible wavelength observations with MIR data from the Spitzer Space Telescope to construct spectral energy distributions (SEDs). These SEDs form the basis of all the results presented here. From SEDs fit to the photometry, I measure galaxy stellar masses and star formation rates (SFRs), and I identify AGN based on the observed shapes of the SEDs. I also estimate the expected X-ray luminosities of the host galaxies of X-ray point sources based on their measured stellar masses and SFRs, and I identify sources whose observed X-ray luminosities show a significant excess as AGN. The two techniques return very different samples, and only 8 of the 44 identified AGN fall in both samples. The host galaxies of the two AGN samples differ significantly in their specific SFRs: the hosts of IR AGN have much larger sSFR than the X-ray AGN hosts. However, the AGN samples show similar distributions of SFRs and have indistinguishable SFR-accretion relations. This suggests that the difference between the IR and X-ray AGN is driven by the gas fraction in the host galaxies, and the IR AGN would be observed as X-ray AGN if the host galaxy did not introduce any absorption. The AGN show no significant bias in R/R200 to the positions of cluster galaxies as a whole. This distinguishes them from star forming galaxies (SFGs), which show a strong preference to be located away from the cluster center. A partial correlation analysis shows that this trend is more closely related to R/R200 than to projected galaxy density, which suggests that the SFR-density relation in clusters is driven by gas processes rather than by interactions between individual galaxies. The radial dependence of the average SFR is consistent with expectations from gas starvation within large observational uncertainties, and it is at least partially driven by changes in the SFRs of individual galaxies. This is (open full item for complete abstract)

Committee: Louis Martini PhD (Advisor); Christopher Kochanek PhD (Committee Member); David Weinberg PhD (Committee Member) Subjects: Astronomy

Doctor of Philosophy, The Ohio State University, 2010, Astronomy

We present the complete results from two, high sampling-rate, multi-month, spectrophotometric reverberation mapping campaigns undertaken to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity active galactic nuclei (AGNs). We have reliably measured the time delay between variations in the continuum and Hβ emission line in seven local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) RBLR-L relationship, where our results remove many outliers and significantly reduce the scatter at the low-luminosity end of this relationship. A detailed analysis of the data from our high sampling rate, multi-month reverberation mapping campaign in 2007 reveals that the Hβ emission region within the BLRs of several nearby AGNs exhibit a variety of kinematic behaviors. Through a velocity-resolved reverberation analysis of the broad Hβ emission-line flux variations in our sample, we reconstruct velocity-resolved kinematic signals for our entire sample and clearly see evidence for outflowing, infalling, and virialized BLR gas motions in NGC 3227, NGC 3516, and NGC 5548, respectively. Finally, we explore the nature of systematic errors that can arise in measurements of black hole masses from single-epoch spectra of AGNs by utilizing the many epochs available for NGC 5548 and PG1229+204 from reverberation mapping databases. In particular, we examine systematics due to AGN variability, contamination due to constant spectral components (i.e., narrow lines and host galaxy flux), data quality (i.e., signal-to-noise ratio, S/N), and blending of spectral features. We investigate the effect that each of these systematics has on the precision and accuracy of single-epoch masses calculated from two commonly-used line-width measures by comparing these results to recent r (open full item for complete abstract)

Committee: Bradley M. Peterson PhD (Advisor); Richard W. Pogge PhD (Committee Member); B. Scott Gaudi PhD (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, The Ohio State University, 2006, Physics

After reviewing the pillars of the concordance cosmology, which serves as the framework of this thesis, I describe how the accretion history of the Universe is revealed by thermal X-ray emission from the stellar sytems and nuclear regions of galaxies. I then go on to discuss how my collaborators and I have used this information to trace the formation of stars and the growth of supermassive black holes over the last ~ 8 Gyrs, i.e., from z ~ 1 to the present. It is of great importance for our understanding of galaxy evolution to determine whether there is a break or a continuum in these processes from the powerful quasars and starbursts of the past, to the seemingly dormant, "normal" galaxies more typical of the present epoch. To help settle the question, we combined optical data from the NOAO Deep Wide-Field Survey (NDWFS), X-ray data from the XBootes survey, and spectral information from the AGN and Galaxy Evolution Survey (AGES) in order to simultaneously obtain deep and wide coverage of the normal galaxy population. In this manner, my collaborators and I were able to bridge the gap in normal galaxy X-ray coverage between large-area local surveys and high redshift, small volume deep fields. Our findings suggest the accretion history of the Universe plays out as a continuum, with the growth of stellar populations and supermassive black holes steadily tailing off rather than abruptly ceasing as we move toward the faint end of the luminosity function.

Committee: Terry Walker (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy (PhD), Ohio University, 2007, Physics (Arts and Sciences)

We present an analysis of star formation, cooling, and feedback in 61 galaxies at the cores of galaxy clusters. A subsample of 33 of these systems possesses cavities in the intracluster medium (ICM) inflated by radio jets emanating from their active galactic nuclei (AGN). We present an extensive analysis of the X-ray cavities in these systems. We find that AGN, through their cavities alone, are energetically able to balance radiative losses (cooling) from the ICM in more than half of these systems. Using the cavity (jet) powers, we place strong lower limits on the rate of growth of supermassive black holes in central galaxies, and we find that they are growing at an average rate of ~ 0.1 M sumyr -1, with some systems growing as quickly as ~ 1 M sunyr -1. We find a trend between bulge growth (star formation) and black hole growth that is approximately in accordance with the slope of the local (Magorrian) relation between black hole and bulge mass. However, the large scatter in the trend suggests that bulges and black holes do not always grow in lock step. With the exception of the rapidly accreting supercavity systems (e.g, MS 0735.6+7421), the black holes are accreting well below their Eddington rates. Most systems could be powered by Bondi accretion from the hot ICM, provided the central gas density increases into the Bondi radius as ρ ∝ r -1. However, if the gas density profile flattens into a core, as observed in M87, Bondi accretion is unlikely to be driving the most powerful outbursts. Using a subsample of 17 systems with published star formation rates, we examine the relationship between cooling and star formation. We find that the star formation rates are approaching or are comparable to X-ray and far-UV limits on the rates of gas condensation onto the central galaxy. The remaining radiative losses could be offset by AGN feedback. The vast gulf between radiative losses and the sink of cooling material, which has been the primary objection to cooling flows, ha (open full item for complete abstract)

Committee: Brian McNamara (Advisor) Subjects: Physics, Astronomy and Astrophysics