arXiv subjects

Kastytis Zubovas

Publications and source records attributed to Kastytis Zubovas.

39 records · Page 3Linked to original sources

arXiv2012

AGN Winds and the Black-Hole - Galaxy Connection

During the last decade, wide-angle powerful outflows from AGN, both on parsec and kpc scales, have been detected in many galaxies. These outflows are widely suspected to be responsible for sweeping galaxies clear of their gas. We present the analytical model describing the propagation of such outflows and calculate their observable properties. Large-scale AGN-driven outflows should have kinetic luminosities \sim ηL_Edd/2 \sim 0.05L_Edd and momentum rates \sim 20L_Edd/c, where L_Edd is the Eddington luminosity of the central black hole and η \sim 0.1 its radiative accretion efficiency. This creates an expanding two-phase medium in which molecular species coexist with hot gas, which can persist after the central AGN has switched off. This picture predicts outflow velocities \sim 1000 - 1500 km/s and mass outflow rates up to 4000 M_\odot/yr on kpc scales, fixed mainly by the host galaxy velocity dispersion (or equivalently black hole mass). We compare our prediction with recent observational data, finding excellent agreement, and suggest future observational tests of this picture.

astro-ph.GA↗

arXiv2012

Clearing Out a Galaxy

It is widely suspected that AGN activity ultimately sweeps galaxies clear of their gas. We work out the observable properties required to achieve this. Large-scale AGN-driven outflows should have kinetic luminosities $\sim η\le/2 \sim 0.05\le$ and momentum rates $\sim 20\le/c$, where $\le$ is the Eddington luminosity of the central black hole and $η\sim 0.1$ its radiative accretion efficiency. This creates an expanding two-phase medium in which molecular species coexist with hot gas, which can persist after the central AGN has switched off. This picture predicts outflow velocities $\sim 1000 - 1500$ km\,s$^{-1}$ and mass outflow rates up to $4000 \msun\,{\rm yr}^{-1}$ on kpc scales, fixed mainly by the host galaxy velocity dispersion (or equivalently black hole mass). All these features agree with those of outflows observed in galaxies such as Mrk231. This strongly suggests that AGN activity is what sweeps galaxies clear of their gas on a dynamical timescale and makes them red and dead. We suggest future observational tests of this picture.

astro-ph.GA↗

arXiv2011

Sgr A* flares: tidal disruption of asteroids and planets?

It is theoretically expected that a supermassive black hole (SMBH) in the centre of a typical nearby galaxy disrupts a Solar-type star every ~ 10^5 years, resulting in a bright flare lasting for months. Sgr A*, the resident SMBH of the Milky Way, produces (by comparison) tiny flares that last only hours but occur daily. Here we explore the possibility that these flares could be produced by disruption of smaller bodies - asteroids. We show that asteroids passing within an AU of Sgr A* could be split into smaller fragments which then vaporise by bodily friction with the tenuous quiescent gas accretion flow onto Sgr A*. The ensuing shocks and plasma instabilities may create a transient population of very hot electrons invoked in several currently popular models for Sgr A* flares, thus producing the required spectra. We estimate that asteroids larger than ~ 10 km in size are needed to power the observed flares, with the maximum possible luminosity of the order 10^39 erg s^-1. Assuming that the asteroid population per parent star in the central parsec of the Milky Way is not too dissimilar from that around stars in the Solar neighbourhood, we estimate the asteroid disruption rates, and the distribution of the expected luminosities, finding a reasonable agreement with the observations. We also note that planets may be tidally disrupted by Sgr A* as well, also very infrequently. We speculate that one such disruption may explain the putative increase in Sgr A* luminosity ~ 300 yr ago.

astro-ph.GA↗