The center of every large galaxy is believed to host a supermassive black hole (SMBH). In some of these galaxies, the nuclear region is extremely luminous and far outshines the entire stellar population. Called active galactic nuclei (AGN), these central sources are equally fascinating and perplexing. Due to their immense distance and small size, modern observation techniques are unable to resolve the structure of these regions. However, the polarization of scattered light carries the imprint of the geometry and kinematics of both the sources and the scattering medium. Here, we present a study of the broad H$\alpha$ lines in a sample of 46 AGN.
Following the work of Smith et al. 2002, 2004, and 2005, we show supporting evidence for the proposed two-component scattering model of AGN using the largest sample of spectropolarimetric observations of broad-line AGN assembled to date. Objects of differing polarization classifications (equatorial or polar) are shown to have significant differences in their distributions of both total flux and polarized flux inter-percentile velocity values. Furthermore, clear distinctions between these classifications are found in polarization position angle and core polarization percentage. These results are supported by Kolmogorov-Smirnov tests between the classifications and are in accordance with those suggested by previous studies.
We also explore the validity of a spectropolarimetric method of estimating SMBH masses. In general, SMBH mass estimates require information on the inclination of the object in the sky, but we can avoid requiring this information by using polarized inter-percentile velocity measurements instead. Using this method, we achieve estimates on the order of 10^6 to 10^8 solar masses -- estimations consistent with both the expected values and those in the literature.
Library of Congress Subject Headings
Active galactic nuclei; Polarization (Light); Black holes (Astronomy)--Observations
Astrophysical Sciences and Technology (MS)
Department, Program, or Center
School of Physics and Astronomy (COS)
Lake, Brian Christopher, "Polarization Properties of Broad Lines in Active Galactic Nuclei" (2020). Thesis. Rochester Institute of Technology. Accessed from
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