Universität zu Köln

Bhat, Harshitha K. (2023). Physical Processes around Galactic Nuclei. PhD thesis, Universität zu Köln.

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Abstract

Supermassive Black Holes (SMBHs) located at the center of the galaxies and their activities in their immediate surroundings impact the properties and evolution of their host galaxy. This influence can be attributed to various factors, including radiation pressure, the interaction of radio plasma with Interstellar Medium (ISM), Active Galactic Nucleus outflows, and/or relativistic jets that inject energy and transport gas from the center to the other regions of the galaxy. In my thesis, I explore the physical processes and interactions in three different black hole environments: AGNs with HMBHs, the Galactic Centre, and Green Pea/Bean galaxies with fading AGNs. Black holes with masses over $10^{10} M_{\odot}$ have ionizing UV spectra that create broad and narrow emission lines in quasars by interacting with the surrounding medium. We examined if this phenomenon introduces a statistical bias against detecting Hypermassive black holes (HMBH). We used a correlation between $L_{X}/L_{UV}$ to create spectral energy distributions for black holes with masses $10^{6}-10^{12} M_{\odot}$ This set of SEDs was then used in the photoionization code CLOUDY to predict emission line strengths of numerous clouds using the ‘locally optimally emitting cloud’ model. We discovered that the commonly used optical lines H$\beta$ and H$\alpha$ decline rapidly at higher BH masses. Instead, the UV lines O VI 1034 \AA $ $ and C IV 1549 \AA $ $ are better suited to detect HMBH. Using the ratio of the narrow emission lines in BPT diagrams, we found that HMBH may be misclassified as star-forming galaxies instead of AGN. We studied the Galactic Center using MIR emission, observing dust features along the mini-spiral and detecting several resolved filaments and clumps. We report the proper motions, temperatures, spectral indices, and flux densities of these sources. We also identified stream-like motion of extended clumps along the mini-spiral, and MIR counterparts of the radio tail components of the IRS7 source. Additionally, we analyzed the shape and orientation of the extended late-type IRS3 star, which is consistent with the ALMA sub-mm detection of the source. We studied 'Green Peas' or 'Green Beans' galaxies with strong [OIII] 5007\AA $ $ emissions. We selected high [OIII] emitting galaxies from a larger sample and conducted LBT-MODS long-slit spectroscopy on the 12 closest sources. We found that there is no preferential direction for NLR extension, indicating no impact of jets on the EELR. The extension in [OII] is extended much further along the galactic plane when compared to [OIII].

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Bhat, Harshitha K. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-712762
Date:	12 October 2023
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	Natural sciences and mathematics Physics
Uncontrolled Keywords:	Keywords Language Observational Astrophysics English Galactic Center English Active Galactic Nuclei English
Date of oral exam:	8 March 2023
Referee:	Name Academic Title Eckart, Andreas Prof. Dr. Labadie, Lucas Prof. Dr. Zensus, Anton Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/71276