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  ≳ 6, only one object, J0100+2802 ( z  = 6.327), was found hosting a >10 10 M ⊙ supermassive black hole. In order to investigate the host galaxy properties of J0100+2802, we performed multi-band ALMA observations, aiming at mapping the dust continuum, [C ii ] and CO(6–5) emission lines with subkiloparsec 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 major  = 3.6 ± 0.2 kpc from the high-resolution continuum observations. No ordered motion on kiloparsec scales was found in either the [C ii ] or the CO(6–5) emission. The velocity dispersion is measured to be 161 ± 7 km s −1 , which is about three times smaller than that estimated from the local M – σ relation. In addition, we found that the CO emission is more concentrated (a factor of 1.8 ± 0.4) than the [C ii ] emission. Together with CO(2–1) detected by the Very Large Array (VLA), we measured the CO spectral line energy distribution, which is best fit by a two-component model that includes a cool component at ∼24 K with a density of cm −3 , and a warm component at ∼224 K with a density of cm −3 . We also fit the dust continuum with a graybody model. This indicated that the continuum has either a high dust emissivity β  ≳ 2 or a hot dust temperature T dust  ≳ 60 K, or a combination of these two factors. The highly excited CO emission and hot dust temperature suggest that the powerful active galactic nucleus in J0100+2802 could contribute to the gas and dust heating, but future observations are needed to confirm this.