The Decoupled Kinematics of high-z QSO Host Galaxies and their Lya halos

TL;DR

This study compares the spatial and kinematic properties of Lya halos and host galaxy interstellar medium in high-redshift QSOs, revealing that halo gas kinematics are decoupled from the galaxy, indicating complex halo dynamics.

Contribution

First detailed comparison of Lya halo and [CII] kinematics in z~6 QSOs, showing decoupled halo and galaxy dynamics with implications for galaxy evolution models.

Findings

Lya halos extend 3-30 times beyond host galaxy ISM.

Most Lya halos lack ordered velocity fields.

Kinematics of Lya halos do not align with host galaxy [CII] emission.

Abstract

We present a comparison of the interstellar medium traced by [CII] (ALMA), and ionised halo gas traced by Lya (MUSE), in and around QSO host galaxies at z~6. To date, 18 QSOs at this redshift have been studied with both MUSE and high-resolution ALMA imaging; of these, 8 objects display a Lya halo. Using datacubes matched in velocity resolution, we compare and contrast the spatial and kinematic information of the Lya halos and the host galaxies' [CII] (and dust-continuum) emission. We find that the Lya halos extend typically 3-30 times beyond the interstellar medium of the host galaxies. The majority of the Lya halos do not show ordered motion in their velocity fields, whereas most of the [CII] velocity fields do. In those cases where a velocity gradient can be measured in Lya, the kinematics do not align with those derived from the [CII] emission. This implies that the Lya emission is not tracing the outskirts of a large rotating disk that is a simple extension of the central galaxy seen in [CII] emission. It rather suggests that the kinematics of the halo gas are decoupled from those of the central galaxy. Given the scattering nature of Lya, these results need to be confirmed with JWST IFU observations that can constrain the halo kinematics further using the non-resonant Ha line.