No evidence for [CII] halos or high-velocity outflows in z>6 quasar host galaxies

TL;DR

This study uses ALMA observations to analyze the interstellar medium in z>6 quasar host galaxies, finding no evidence for [CII] halos or high-velocity outflows, and characterizing the spatial distribution of gas and dust.

Contribution

It provides the first detailed analysis of the spatial extent of [CII] and dust emission in high-redshift quasar hosts, showing no signs of halos or outflows.

Findings

Surface brightness profiles are steep within 2kpc and shallower up to 10kpc.

No broad [CII] line emission indicative of outflows was detected.

Extended emission is consistent with star formation-driven dust emission.

Abstract

We study the interstellar medium in a sample of 27 high-redshift quasar host galaxies at z>6, using the [CII] 158um emission line and the underlying dust continuum observed at ~1kpc resolution with ALMA. By performing uv-plane spectral stacking of both the high and low spatial resolution data, we investigate the spatial and velocity extent of gas, and the size of the dust-emitting regions. We find that the average surface brightness profile of both the [CII] and the dust continuum emission can be described by a steep component within a radius of 2kpc, and a shallower component with a scale length of 2kpc, detected up to ~10kpc. The surface brightness of the extended emission drops below ~1% of the peak at radius of ~5kpc, beyond which it constitutes 10-20% of the total measured flux density. Although the central component of the dust continuum emission is more compact than that of the [CII] emission, the extended components have equivalent profiles. The observed extended components are consistent with those predicted by hydrodynamical simulations of galaxies with similar infrared luminosities, where the dust emission is powered by star formation. The [CII] spectrum measured in the mean uv-plane stacked data can be described by a single Gaussian, with no observable [CII] broad-line emission (velocities in excess of >500km/s), that would be indicative of outflows. Our findings suggest that we are probing the interstellar medium and associated star formation in the quasar host galaxies up to radii of 10kpc, whereas we find no evidence for halos or outflows.