Why are AGN found in High Mass Galaxies?

Abstract

We use semi-analytic models implemented in the Millennium Simulation to analyze the merging histories of dark matter haloes and of the galaxies that reside in them. We assume that supermassive black holes only exist in galaxies that have experienced at least one major merger. Only a few percent of galaxies with stellar masses less than $M_{\ast }<10^{10}{M}_{\odot }$ are predicted to have experienced a major merger and to contain a black hole. The fraction of galaxies with black holes increases very steeply at larger stellar masses. This agrees well with the observed strong mass dependence of the fraction of nearby galaxies that contain either low-luminosity (LINER-type) or higher-luminosity (Seyfert or composite-type) AGN. We then investigate when the major mergers that first create the black holes are predicted to occur. High mass galaxies are predicted to have formed their black holes at very early epochs. The majority of low mass galaxies never experience a major merger and hence do not contain a black hole, but a significant fraction of the supermassive black holes that do exist in low mass galaxies are predicted to have formed recently.

7 pages,7 figures, MNRAS submitted

References in corpus (4)

• Galaxy Evolution from Halo Occupation Distribution Modeling of DEEP2 and SDSS Galaxy Clustering
• Ram pressure stripping the hot gaseous halos of galaxies in groups and clusters
• Modelling and interpreting the dependence of clustering on the spectral energy distributions of galaxies
• Morphologies of AGN host galaxies using HST/ACS in the CDFS-GOODS field

Cited by in corpus (1)

• Simulating Subhalos at High Redshift: Merger Rates, Counts, and Types