The Atacama Cosmology Telescope: measuring radio galaxy bias through
  cross-correlation with lensing
  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 $\log(M_{\rm halo} / M_\odot) = 13.6^{+0.3}_{-0.4}$.
