Spatially resolved molecular interstellar medium in a $z=6.6$ quasar host galaxy

TL;DR

This study uses high-resolution observations of multiple ISM tracers in a $z=6.6$ quasar host galaxy to analyze the spatial distribution, kinematics, and properties of different gas phases, revealing that CO and dust trace similar regions while [CII] is more extended.

Contribution

First detailed spatially resolved analysis of multiple ISM phases in a $z=6.6$ quasar host galaxy, comparing their distributions and ratios.

Findings

CO and dust continuum are less extended than [CII]

Radial ratios suggest decreasing dust optical depth with radius

No significant ISM differences between quasar and companion galaxies

Abstract

We present high spatial resolution (0.4", 2.2kpc) observations of the CO(6-5), CO(7-6) and [CI] lines and dust continuum emission from the interstellar medium in the host galaxy of the quasar J0305$-$3150 at $z=6.6$. These, together with archival [CII] data at comparable spatial resolution, enable studies of the spatial distribution and kinematics between the ISM in different phases. When comparing the radial profiles of CO, [CII] and the dust continuum, we find that the CO and dust continuum exhibit similar spatial distributions, both of which are less extended than the [CII], indicating that the CO and dust continuum are tracing the same gas component, while the [CII] is tracing a more extended one. In addition, we derive the radial profiles of the [CII]/CO, [CII]/far-infrared (FIR), CO/FIR, and dust continuum $S_{98.7 \rm GHz}/S_{258.1 \rm GHz}$ ratios. We find a decreasing $S_{98.7 \rm GHz}/S_{258.1 \rm GHz}$ ratio with radius, possibly indicating a decrease of dust optical depth with increasing radius. We also detect some of the ISM lines and continuum emission in the companion galaxies previously discovered in the field around J0305$-$3150. Through comparing the line-to-line and line-to-FIR ratios, we find no significant differences between the quasar and its companion galaxies.