The Decoupled Kinematics of High-z QSO Host Galaxies and Their Lyα Halos

Abstract

We present a comparison of the interstellar medium traced by [C ii ] (Atacama Large Millimeter/submillimeter Array), and ionized halo gas traced by Ly α (Multi Unit Spectroscopic Explorer), 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 Ly α halo. Using data cubes matched in velocity resolution, we compare and contrast the spatial and kinematic information of the Ly α halos and the host galaxies’ [C ii ] (and dust-continuum) emission. We find that the Ly α halos extend typically 3−30 times beyond the interstellar medium of the host galaxies. The majority of the Ly α halos do not show ordered motion in their velocity fields, whereas most of the [C ii ] velocity fields do. In those cases where a velocity gradient can be measured in Ly α , the kinematics do not align with those derived from the [C ii ] emission. This implies that the Ly α emission is not tracing the outskirts of a large rotating disk, which is a simple extension of the central galaxy seen in [C ii ] emission. It rather suggests that the kinematics of the halo gas are decoupled from those of the central galaxy. Given the scattering nature of Ly α , these results need to be confirmed with James Webb Space Telescope Integral Field Unit observations that can constrain the halo kinematics further using the nonresonant H α line.