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Low-Redshift z < 0.2 Quasars: QSO and Host Galaxy Relationship

Presentation #529.03 in the session “Quasars”.

Published onJan 11, 2021
Low-Redshift z < 0.2 Quasars: QSO and Host Galaxy Relationship

Quasars are among the most energetic phenomena in the universe, but their origins remain elusive. Are quasars the result of external gravitational interactions or are they instead the result of processes that occur within the host galaxy itself? To answer our question, we analyze a sample of 357 quasi-stellar objects (QSOs) which were selected by matching two million objects from the first epoch of the VLA Sky Survey (VLASS) with the Gaia DR2 catalog, removing those objects with high proper motion, and restricting our search to objects with optical magnitude g < 17 and with z < 0.2. Out of our 357 quasar sources, 342 had optical galaxy images that we could analyze. The narrow redshift range allowed us to observe quasars that live in the same epoch and the low redshift of our sample allowed us to more easily see optical features in the host galaxies. We qualitatively and quantitatively classified our quasar images to detect different galaxy morphologies that may give clues about gravitational interactions occurring in each host galaxy. We visually classified the presence of extended emission, the galaxy type of our host galaxy, as well as noted the presence of close companions or mergers. We found that 77% of our sources were hosted by elliptical galaxies, 18% were hosted by spiral galaxies, and 5% by galaxies demonstrating tidal tail features. To objectively characterize our hosts, we calculated the rotational asymmetry, the Gini Coefficient, and the Second Order Moment of Brightness (M20) for our 342 quasars, and did a Principal Component Analysis to find the most significant relationship when plotted against luminosity and found that while the Asymmetry and M20 had only a minor correlation with luminosity, higher Gini Values correlated with smaller values in both optical and radio luminosity and in their luminosity ratio (radio/optical).

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