ALMA Observations of Quasar Host Galaxies at z ≃ 4.8

Abstract

We present ALMA Band 7 data of the [C II] $\lambda 157.74\,\mu {\rm{m}}$ emission line and underlying far-IR (FIR) continuum for 12 luminous quasars at $z\simeq 4.8$ powered by fast-growing supermassive black holes (SMBHs). Our total sample consists of 18 quasars, 12 of which are presented here for the first time. The new sources consist of six Herschel/SPIRE-detected systems, which we define as "FIR-bright" sources, and six Herschel/SPIRE-undetected systems, which we define as "FIR-faint" sources. We determine dust masses for the quasars hosts of ${M}_{\mathrm{dust}}\leqslant 0.2\mbox{--}25.0\times {10}^{8}{M}_{\odot }$ , implying interstellar medium gas masses comparable to the dynamical masses derived from the [C II] kinematics. It is found that, on average, the Mg II line is blueshifted by $\sim 500\,\mathrm{km}\,{{\rm{s}}}^{-1}$ with respect to the [C II] emission line, which is also observed when complementing our observations with data from the literature. We find that all of our FIR-bright subsample and most of the FIR-faint objects lie above the main sequence of star-forming galaxies at $z\sim 5$ . We detect companion submillimeter galaxies for two sources, both FIR-faint, with a range of projected distances of $\sim 20\mbox{--}60$ kpc and typical velocity shifts of $\left|{\rm{\Delta }}V\right|\lesssim 200\,\mathrm{km}\,{{\rm{s}}}^{-1}$ from the quasar hosts. Of our total sample of 18 quasars, 5/18 are found to have dust-obscured star-forming companions.