Supermassive Black Holes and Their Environments

TL;DR

This study uses high-resolution hydrodynamic simulations to explore the relationships between supermassive black holes, their host halos, and large-scale environments, revealing environmental influences on black hole growth and activity.

Contribution

It provides the first detailed simulation-based analysis of black hole-environment relations across different cosmic densities and redshifts, highlighting environmental effects on black hole evolution.

Findings

Black hole and halo mass relations are well-defined at low redshifts.

High-redshift black holes are more prevalent in group environments.

Star formation correlates more strongly with local density than black hole activity.

Abstract

We make use of the first high--resolution hydrodynamic simulations of structure formation which self-consistently follows the build up of supermassive black holes introduced in Di Matteo et al. (2007) to investigate the relation between black holes (BH), host halo and large--scale environment. There are well--defined relations between halo and black hole masses and between the activities of galactic nuclei and halo masses at low redshifts. A large fraction of black holes forms anti--hierarchically, with a higher ratio of black hole to halo mass at high than at low redshifts. At $z=1$, we predict group environments (regions of enhanced local density) to contain the highest mass and most active (albeit with a large scatter) BHs while the rest of the BH population to be spread over all densities from groups to filaments and voids. Density dependencies are more pronounced at high rather than low redshift. These results are consistent with the idea that gas rich mergers are likely the main regulator of quasar activity. We find star formation to be a somewhat stronger and tighter function of local density than BH activity, indicating some difference in the triggering of the latter versus the former. There exists a large number of low--mass black holes, growing slowly predominantly through accretion, which extends all the way into the most underdense regions, i.e. in voids.