A Spatially Resolved [C ii] Survey of 31 z ∼ 7 Massive Galaxies Hosting Luminous Quasars

Abstract

The [C ii ] 158 μ m emission line and the underlying far-infrared (FIR) dust continuum are important tracers for studying star formation and kinematic properties of early galaxies. We present a survey of the [C ii ] emission lines and FIR continua of 31 luminous quasars at z > 6.5 using the Atacama Large Millimeter Array (ALMA) and the NOrthern Extended Millimeter Array at sub-arcsec resolution. This survey more than doubles the number of quasars with [C ii ] and FIR observations at these redshifts and enables statistical studies of quasar host galaxies deep into the epoch of reionization. We detect [C ii ] emission in 27 quasar hosts with a luminosity range of L _[C _II _] = (0.3–5.5) × 10 ^9 L _⊙ and detect the FIR continuum of 28 quasar hosts with a luminosity range of L _FIR = (0.5–13.0) × 10 ^12 L _⊙ . Both L _[C _II _] and L _FIR are correlated ( ρ ≃ 0.4) with the quasar bolometric luminosity, albeit with substantial scatter. The quasar hosts detected by ALMA are clearly resolved with a median diameter of ∼5 kpc. About 40% of the quasar host galaxies show a velocity gradient in [C ii ] emission, while the rest show either dispersion-dominated or disturbed kinematics. Basic estimates of the dynamical masses of the rotation-dominated host galaxies yield M _dyn = (0.1–7.5) × 10 ^11 M _⊙ . Considering our findings alongside those of literature studies, we found that the ratio between M _BH and M _dyn is about 10 times higher than that of local M _BH – M _dyn relation on average but with substantial scatter (the ratio difference ranging from ∼0.6 to 60) and large uncertainties.

Keywords

• Early universe
• Galaxies
• Quasars
• Supermassive black holes