Measuring the Dark Matter Halo Mass of X-ray AGN at z~1 using photometric redshifts

TL;DR

This study estimates the dark matter halo mass of X-ray AGN at z~1 using a novel method that combines spectroscopic and photometric redshift data, revealing most AGN reside in moderate mass haloes and supporting cold gas accretion as a growth mechanism.

Contribution

It introduces a new cross-correlation method that uses photometric redshift PDFs for galaxies, reducing the need for galaxy spectroscopy in halo mass measurements.

Findings

Estimated halo mass of ~13h^{-1} M_solar for X-ray AGN at z~1.

Removing AGN in X-ray groups decreases halo mass estimate by 0.5 dex.

Most AGN are found in moderate mass dark matter haloes.

Abstract

Data from the AEGIS, COSMOS and ECDFS surveys 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 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 ~13h-1M_solar, 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 favour cold gas accretion as the main channel of supermassive black hole growth for most X-ray AGN.