Author ORCID Identifier
Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
Dr. D. Michael Crenshaw
Active Galactic Nuclei (AGN) are the luminous centers of galaxies, powered by supermassive black holes (SMBHs) that are actively feeding on the surrounding matter. This feeding process creates massive amounts of electromagnetic radiation from the accretion disk of the SMBH, which can interact with the circumnuclear environment and drive the gas away from the nucleus, producing SMBH feedback in the form of powerful winds of ionized and/or molecular gas outflows. Ionized gas outflows, observed in the Narrow Line Regions (NLRs) of active galaxies, are thought to play a crucial role in regulating the growth of the SMBHs and galaxy bulges. However, the physical mechanisms responsible for the origin and acceleration of these outflows are yet to be explained. Additionally, their overall impact on star formation needs to be quantified for the realistic simulations of large-scale structure formation and evolution.
We present an in-depth analysis of outflow dynamics in a sample of 5 nearby active galaxies using spatially-resolved spectroscopic and imaging observations. First, we map the kinematic structure of the ionized gas and outflows using multiple long-slit spectra. We then derive the stellar mass distribution of the host galaxy as a function of distance from the nucleus, using 2D surface brightness decomposition of high-resolution broadband images. Finally, we determine the launch distances of the observed outflows using an analytical model based on radiative driving by the AGN and gravitational deceleration due to the SMBH and enclosed mass of the galaxy. These launch distances may correspond to the star-forming gas reservoir sites. Our models successfully reproduce the distinct velocity and mass outflow rate profiles observed in spatially resolved measurements, particularly the turnover distances where host galaxy gravity starts to overwhelm radiation pressure. This consistency between observed and model kinematics proves that the AGN radiation pressure is the primary driving mechanism responsible for the observed NLR outflows in these galaxies. Further, we find that the maximum distances from which the outflows originate increase with AGN luminosity, which indicates that a more powerful AGN may be efficient enough to provide negative feedback required for bulge quenching. In the future, these results will provide significant constraints on the outflows in the high redshift galaxies, which may dominate feedback in the early universe but lack spatially resolved information.
Meena, Beena, "The Dynamics of Narrow Line Region Outflows in Nearby Active Galaxies." Dissertation, Georgia State University, 2022.
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