MUSE-ALMA Haloes XV: Cold molecular, ionised, and stellar kinematics of HI-rich galaxies at z $\sim$ 0.5

Abstract

Spatially resolved galaxy kinematics are well studied at z $\sim$ 0 and z > 1, revealing that disks are common out to z $\sim 3-6$, albeit with higher velocity dispersions. z $\sim$ 0.5 marks a key transition in the drivers of disk turbulence and baryonic-dark matter mass budgets, yet multi-tracer resolved kinematic studies remain rare beyond the local Universe. We exploit a unique dataset combining ALMA CO observations with MUSE ionised gas and stellar continuum data to study the resolved kinematics of six galaxies at 0.43 < z < 0.83, part of the MUSE-ALMA Haloes program, selected via their association with H I absorption systems and spanning stellar masses from log$(M_{\star }/M_{\odot })=10.1-11.8$. Combining new ALMA/CO data with existing MUSE H$\beta$ kinematics and HST morphologies, we classify galaxies using morpho-kinematic criteria. For rotating disks, we jointly model H$\beta$ and CO(2-1) kinematics with DYSMALPY and compare results to theoretical predictions for pressure support, while pPXF is used to fit stellar absorption features. Four of the six galaxies are classified as disks, with two having known group members. These disks show elevated gas velocity dispersions relative to z $\sim$ 0 disks, consistent with interpolated trends between z $\sim$ 0 and z > 1. The results support marginally stable gaseous disks where gravitational instability still contributes alongside stellar feedback, with tentative evidence for a dynamically hotter warm ionised phase relative to cold gas (${\sigma }_{0,H\beta }\sim 1.7\times {\sigma }_{0,CO}$). We derive an average dark matter fraction $⟨f_{DM}⟩=0.42\pm 0.14$, consistent with observations at similar redshifts, stellar masses, and surface densities. This work demonstrates the value of self-consistent, multi-wavelength analyses for probing disk settling physics in a relatively unexplored redshift range.

Published in A&A, 17 pages + Appendix. Part of the MUSE-ALMA survey series, see simultaneously posted papers by Peroux et al. and O'Beirne et al