Measuring the dark matter halo mass of X-ray agn at Z ∼ 1 using photometric redshifts

Abstract

Data from the All Wavelength Extended Groth strip International Survey (AEGIS), Cosmological evolution Survey (COSMOS) and Extended Chandra Deep Field-South Survey (ECDFS) are combined to infer the bias and dark matter halo mass of moderate luminosity [LX(2-10 keV)=42.9 erg s-1] X-ray active galactic nuclei (AGN) at z ≈ 1 via their cross-correlation function with galaxies. In contrast to standard cross-correlation function estimators, we present a method that requires spectroscopy only for the AGN and uses photometric redshift probability distribution functions for galaxies to determine the projected real-space AGN/galaxy cross-correlation function. The estimated dark matter halo mass of X-ray AGN in the combined AEGIS, COSMOS and ECDFS fields is ≈13 h-1 M⊙, in agreement with previous studies at similar redshift and luminosity ranges. Removing from the sample the 5 per cent of the AGN associated with X-ray selected groups results in a reduction by about 0.5 dex in the inferred AGN dark matter halo mass. The distribution of AGN in dark matter halo mass is therefore skewed and the bulk of the population lives in moderate mass haloes. This result favours cold gas accretion as the main channel of supermassive black hole growth for most X-ray AGN. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.