Abstract Details

Name: Dipanweeta Bhattacharyya
Affiliation: Indian Institute of Astrophysics, Bangalore
Conference ID: ASI2021_433
Title : Cosmic evolution of black holes and the $M_{\bullet}-\sigma$ relation
Authors and Co-Authors : Dipanweeta Bhattacharyya, Indian Institute of Astrophysics, Bangalore. Thesis supervisor: Prof. Arun Mangalam, Indian Institute of Astrophysics, Bangalore.
Abstract Type : Oral
Abstract Category : Thesis
Abstract : The thesis is devoted to a study of the evolution of black holes and the $M_{\bullet} \propto \sigma^{p}$ relation. We have considered realistic elliptical (spherical) galaxy profiles that are taken to follow a single power-law density profile or the Nuker intensity profile. Assuming a proportionality relation between the black hole mass and bulge mass, $ M_{\bullet} =f_{b} M_b$, and applying this to several galaxies, we found the best fit global $p$ and $f_{b}$, by minimizing $\chi^{2}$, which are consistent with the observed ranges. We have built an evolution model of the central black hole that depends on the processes of gas accretion, stellar capture, mergers, and electromagnetic torque. In the case of gas accretion in the presence of cooling sources, the flow is momentum-driven, after which the black hole reaches a saturated mass; subsequently, it grows only by stellar capture and mergers. We model the evolution of the mass and spin with the initial seed mass and spin in $\Lambda$CDM cosmology. For stellar capture, we have assumed a power-law density profile for the stellar cusp in a framework of relativistic loss cone theory that includes the effects of black hole spin, Carter's constant, loss cone angular momentum, and capture radius. We have considered the merger activity to be effective for $z \lesssim 4$, and we self-consistently include the Blandford--Znajek torque. We calculate these effects on the black hole growth individually and in combination, for deriving the evolution. Before saturation, accretion dominates the black hole growth ($\sim 95\%$ of the final mass), and subsequently, stellar capture and mergers take over with roughly equal contributions. The applications of this model include the evolution of the $M_{\bullet} - \sigma$ relation, black hole archaeology, and formation of supermassive black hole seeds from stellar-mass black holes by stellar capture.