Doctor of Philosophy, The Ohio State University, 2023, Physics

Correlations in and with the flux transmission of the Lyman-alpha (LyA) forest in the spectra of high-redshift quasars are powerful cosmological tools, yet these measurements can be compromised if the intrinsic quasar continuum is significantly uncertain. One particularly problematic case is broad absorption line (BAL) quasars, which exhibit blueshifted absorption associated with many spectral features that are consistent with outflows of up to ~0.1c. As these absorption features can both fall in the forest region and be difficult to distinguish from LyA absorption, cosmological analyses eliminate the ~12 - 16% of quasars that exhibit BALs. This work explores an alternate approach that includes BALs in the LyA auto correlation function, with the exception of the expected locations of the BAL absorption troughs. This procedure is tested on both the SDSS DR14 and DESI Year 1 LyA catalogs, using the reduction of error on the autocorrelations as a metric for success. The masking procedure returns over 95% of the pathlength that is lost by the exclusion of BALs, as well as increases the density of sightlines. It shows that including BAL quasars reduces the fractional uncertainty in the covariance matrix and correlation function by 12% on SDSS DR14 and 20% on DESI Year 1. Furthermore, it does not significantly change the shape of the correlation function relative to analyses that exclude BAL quasars. It also evaluates different definitions of BALs, masking strategies, and potential differences in the quasar continuum in the forest region for BALs with different amounts of absorption.

Committee: Paul Martini (Advisor); Linda Carpenter (Committee Member); Chris Hirata (Committee Member); Klaus Honscheid (Advisor) Subjects: Astronomy; Physics

Doctor of Philosophy, The Ohio State University, 2017, Astronomy

I present the initial results of characterizing moderate redshift (z > 2) quasars in the Dark Energy Survey (DES) by their variability. As the scales associated with supermassive black holes (SMBHs) are too small to be resolved directly, alternative methods are necessary to learn about their structure, how they grow, and how they impact their environments. One such method is through variability. Quasars are naturally variable objects, and by measuring the time delay to different emitting regions as they respond to changes in the extreme ionizing UV photons produced at the inner edge of the disk, we can estimate normally inaccessible size scales associated with SMBHs. This technique is known as reverberation mapping. I first apply this technique to probe accretion disk sizes. Only a handful of such measurements exist in the literature, sampled through reverberation mapping or gravitational microlensing. I measure time delays between the DES photometric bands to place constraints on accretion disk sizes, and then present a software extension to the JAVELIN code that provides a Bayesian framework for fitting a thin accretion disk model directly to the data rather than the individual lags themselves. This is tested on fake data as well as the highest quality dataset available for a local active galaxy, NGC 5548, before being applied to a sample of DES quasars. This new framework, under our thin disk assumption, gives competitive accretion disk sizes for quasars with our survey quality data alone, and adds over a dozen objects to the relatively small number of quasars with measured disk properties. Next, I present the serendipitous discovery of a z=0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in the DES data, spectroscopically confirmed with the Australian Dark Energy Survey (OzDES) project. LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad FeII (an FeLoBAL) and Balme (open full item for complete abstract)

Committee: Paul Martini (Advisor); Christopher Kochanek (Committee Member); Bradley Peterson (Committee Member) Subjects: Astronomy; Astrophysics