A direct measurement of the linear bias of mid-infrared-selected quasars at z~1 using cosmic microwave background lensing

TL;DR

This study directly measures the linear bias of mid-infrared-selected quasars at redshift ~1 using cosmic microwave background lensing, finding that obscured and unobscured quasars trace matter similarly, which informs quasar evolution models.

Contribution

It provides the first direct measurement of quasar bias at z~1 through CMB lensing, confirming that obscured and unobscured quasars have similar clustering properties.

Findings

Bias of quasars measured as 1.67±0.24

Excellent agreement between SPT and Planck lensing maps

Obscured and unobscured quasars trace matter similarly

Abstract

We measure the cross-power spectrum of the projected mass density as traced by the convergence of the cosmic microwave background lensing field from the South Pole Telescope (SPT) and a sample of Type 1 and 2 (unobscured and obscured) quasars at z~1 selected with the Wide-field Infrared Survey Explorer, over 2500 deg^2. The cross-power spectrum is detected at ~7-sigma, and we measure a linear bias b=1.67+/-0.24, consistent with clustering analyses. Using an independent lensing map, derived from Planck observations, to measure the cross-spectrum, we find excellent agreement with the SPT analysis. The bias of the combined sample of Type 1 and 2 quasars determined in this work is similar to that previously determined for Type 1 quasars alone; we conclude that that obscured and unobscured quasars must trace the matter field in a similar way. This result has implications for our understanding of quasar unification and evolution schemes.