# Resolved [CII] Emission from z>6 Quasar Host -- Companion Galaxy Pairs

## TL;DR

This study uses high-resolution ALMA observations to analyze the interstellar medium and dynamics of z>6 quasar host and companion galaxies, revealing turbulence, ordered rotation in some, and tidal interactions, with implications for black hole fueling.

## Contribution

First detailed high-resolution [CII] and dust continuum study of z>6 quasar host-companion pairs, showing diverse ISM properties and interaction effects at early cosmic times.

## Key findings

- [CII] emission is resolved with extents of 3.2-5.4 kpc.
- Galaxies exhibit high velocity dispersions (~80-200 km/s).
- Tidal interactions are observed in close pairs.

## Abstract

We report on ~0.35"(~2 kpc) resolution observations of the [CII] and dust continuum emission from five z>6 quasar host-companion galaxy pairs obtained with the Atacama Large Millimeter/submillimeter Array. The [CII] emission is resolved in all galaxies, with physical extents of 3.2-5.4 kpc. The dust continuum is on-average 40% more compact, which results in larger [CII] deficits in the center of the galaxies. However, the measured [CII] deficits are fully consistent with those found at lower redshifts. Four of the galaxies show [CII] velocity fields that are consistent with ordered rotation, while the remaining six galaxies show no clear velocity gradient. All galaxies have high (~80-200 km/s) velocity dispersions, consistent with the interpretation that the interstellar medium (ISM) of these high redshift galaxies is turbulent. By fitting the galaxies with kinematic models, we estimate the dynamical mass of these systems, which range between (0.3 -> 5.4) x 1E10 Msun. For the three closest separation galaxy pairs, we observe dust and [CII] emission from gas in between and surrounding the galaxies, which is an indication that tidal interactions are disturbing the gas in these systems. Although gas exchange in these tidal interactions could power luminous quasars, the existence of quasars in host galaxies without nearby companions suggests that tidal interactions are not the only viable method for fueling their active centers. These observations corroborate the assertion that accreting supermassive black holes do not substantially contribute to the [CII] and dust continuum emission of the quasar host galaxies, and showcase the diverse ISM properties of galaxies when the universe was less than one billion years old.