Spatially Resolved Interstellar Medium and Highly-Excited Dense Molecular Gas in the Most Luminous Quasar at z=6.327

Abstract

Among more than 200 quasars known at $z\gtrsim 6$, only one object, J0100+2802 (z=6.327), was found hosting a $>10^{10}{M}_{\odot }$ super-massive black hole (SMBH). In order to investigate the host galaxy properties of J0100+2802, we performed multi-band ALMA observations, aiming at mapping the dust continuum, [CII] and CO(6-5) emission lines with sub-kiloparsec scale resolution, as well as detecting high-J CO lines in CO(11-10), CO(10-9), and CO(7-6). The galaxy size is measured to be $R_{\mathrm{major}}=3.6\pm 0.2$ kpc from the high resolution continuum observations. No ordered motion on kilo-parsec scales was found in both [CII] and CO(6-5) emissions. The velocity dispersion is measured to be 161$\pm$7 km s${}^{-1}$, $\sim$3 times smaller than that estimated from the local M-$\ddot{I}ƒ$ relation. In addition, we found that the CO emission is more concentrate (a factor of 1.8$\pm$0.4) than the [CII] emission. Together with CO(2-1) detected by VLA, we measured the CO Spectral Line Energy Distribution (SLED), which is best fit by a two-components model, including a cool component at $\sim 24$ K with a density of $n_{({\mathrm{H}}_2)}$=10${}^{4.5}$ cm${}^{-3}$, and a warm component at $\sim 224$ K with a density of $n_{({\mathrm{H}}_2)}$=10${}^{3.6}$ cm${}^{-3}$. We also fitted the dust continuum with a graybody model, which indicates that it has either a high dust emissivity ${\hat{I}}^2\gtrsim 2$ or a hot dust temperature $T_{\mathrm{dust}}\gtrsim 60$ K, or a combination of both factors. The highly excited CO emission and hot dust temperature suggest that the powerful AGN in J0100+2802 could contribute to the gas and dust heating although future observations are needed to confirm this.

accepted for publication in The Astrophysical Journal