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

Abstract

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