Weighing obscured and unobscured quasar hosts with the CMB

TL;DR

This study uses CMB lensing cross-correlations to measure and compare the halo masses of obscured and unobscured quasars, confirming that obscured quasars reside in significantly more massive halos, with implications for quasar evolution models.

Contribution

It applies CMB lensing cross-correlation to distinguish halo masses of quasar subclasses, providing independent validation of previous clustering results.

Findings

Obscured quasars have higher bias and reside in more massive halos than unobscured quasars.

Halo mass difference is approximately a factor of 3.

Results are consistent with angular clustering measurements within 1 sigma.

Abstract

We cross-correlate a cosmic microwave background (CMB) lensing map with the projected space densities of quasars to measure the bias and halo masses of a quasar sample split into obscured and unobscured populations, the first application of this method to distinct quasar subclasses. Several recent studies of the angular clustering of obscured quasars have shown that these objects likely reside in higher-mass halos compared to their unobscured counterparts. This has important implications for models of the structure and geometry of quasars, their role in growing supermassive black holes, and mutual quasar/host galaxy evolution. However, the magnitude and significance of this difference has varied from study to study. Using data from \planck, \wise, and SDSS, we follow up on these results using the independent method of CMB lensing cross-correlations. The region and sample are identical to that used for recent angular clustering measurements, allowing for a direct comparison of the CMB-lensing and angular clustering methods. At $z \sim 1$, we find that the bias of obscured quasars is $b_q = 2.57 \pm 0.24$, while that of unobscured quasars is $b_q = 1.89 \pm 0.19$. This corresponds to halo masses of $\log (M_h / M_{\odot} h^{-1}) = 13.24_{-0.15}^{+0.14}$ (obscured) and $\log (M_h / M_{\odot} h^{-1}) = 12.71_{-0.13}^{+0.15}$ (unobscured). These results agree well with with those from angular clustering (well within $1\sigma$), and confirm that obscured quasars reside in host halos $\sim$3 times as massive as halos hosting unobscured quasars. This implies that quasars spend a significant portion of their lifetime in an obscured state, possibly more than one half of the entire active phase.