The z=7.54 Quasar ULAS J1342+0928 Is Hosted by a Galaxy Merger

TL;DR

This study uses high-resolution ALMA observations to reveal that the host galaxy of the most distant known quasar at z=7.54 is undergoing a galaxy merger, evidenced by complex [CII] emission and chaotic gas motion.

Contribution

First detailed ALMA imaging of a z=7.54 quasar host showing merger signatures through resolved [CII] and dust emission.

Findings

[CII] emission is more extended than dust continuum.

The [CII] structure is elongated and complex.

Gas kinematics indicate a galaxy merger.

Abstract

We present ALMA 0.28"x0.20" (1.4kpc x 1.0kpc) resolution observations of the [CII] 158um line and underlying dust continuum in the host galaxy of the most distant quasar currently known, ULAS J1342+0928 at z=7.5413. Both the [CII] and continuum are detected and spatially resolved. The [CII] line is ~1.5 times more extended than the continuum emission, showing an elongated and complex structure of approximately 3.2kpc x 6.4kpc. Two separate peaks are clearly seen (>6sigma each) in three 100 km/s width [CII] channel maps. The velocity field of the [CII] gas does not show evidence of a coherent rotation field but rather chaotic motion, reminiscent of an on-going merger.