Gravitational Lensing of CMB by Quasars in SDSS-IV

In this paper we study the cross-correlation between the textit{Planck} CMB lensing convergence map and the eBOSS quasar overdensity obtained from the Sloan Digital Sky Survey (SDSS) IV, in the redshift range $0.9 u003c z u003c 2.2$. We detect a CMB lensing convergence-quasar angular cross power spectrum with $5.4 sigma$ significance. The cross power spectrum provides a measurement of the quasar clustering bias with little to no systematics. The redshift distribution of the quasar sample has a median redshift $z approx 1.55$, and an effective redshift about $1.51$. The best fit bias of the quasar sample is $b_q = 2.43 pm 0.45$, corresponding to halo mass of $log_{10}left( frac{M}{h^{-1} M_odot} right) = 12.54^{+0.25}_{-0.36}$. This is broadly consistent with the previous literature on quasars within the similar redshift range and selection. However, being obtained in cross-correlation with CMB lensing, we expect it to be robust to a wide range of possible systematic effects that may contaminate the auto correlation of quasars. We check for various systematic effects from both CMB lensing and Quasar overdensity maps, and found that all systematics to be consistent with null within $2 sigma$. The data is not sensitive to a possible scale dependence of the bias at present, but we expect that as the number surveyed quasars increases (in future surveys such as DESI), it is likely that strong constraints on the scale dependence of the bias can be obtained.