The Atacama Cosmology Telescope: measuring radio galaxy bias through cross-correlation with lensing

TL;DR

This study measures the bias of radio-loud AGN by cross-correlating radio galaxy positions from the FIRST survey with CMB lensing data from the Atacama Cosmology Telescope, revealing their typical halo masses.

Contribution

It provides the first measurement of radio galaxy bias through cross-correlation with CMB lensing, constraining halo masses of radio-loud AGN at high redshift.

Findings

Bias of radio-loud AGN is approximately 3.5 at redshift 1.5.

Radio AGN reside in halos with mass around 10^13.6 solar masses.

Cross-correlation detection significance is 4.4 sigma.

Abstract

We correlate the positions of radio galaxies in the FIRST survey with the CMB lensing convergence estimated from the Atacama Cosmology Telescope over 470 square degrees to determine the bias of these galaxies. We remove optically cross-matched sources below redshift $z=0.2$ to preferentially select Active Galactic Nuclei (AGN). We measure the angular cross-power spectrum $C_l^{\kappa g}$ at $4.4\sigma$ significance in the multipole range $100<l<3000$, corresponding to physical scales between $\approx$ 2--60 Mpc at an effective redshift $z_{\rm eff}= 1.5$. Modelling the AGN population with a redshift-dependent bias, the cross-spectrum is well fit by the Planck best-fit $\Lambda$CDM cosmological model. Fixing the cosmology we fit for the overall bias model normalization, finding $b(z_{\rm eff}) = 3.5 \pm 0.8$ for the full galaxy sample, and $b(z_{\rm eff})=4.0\pm1.1 (3.0\pm1.1)$ for sources brighter (fainter) than 2.5 mJy. This measurement characterizes the typical halo mass of radio-loud AGN: we find $\log(M_{\rm halo} / M_\odot) = 13.6^{+0.3}_{-0.4}$.