Evolution of gas velocity dispersion in discs from <i>z</i> ∼ 8 to <i>z</i> ∼ 0.5

ABSTRACT Together, optical/near-infrared integral field spectroscopy and resolved submillimetre interferometry data have mapped the ionized and molecular gas motions in nearly a thousand galaxies at redshifts $z&amp;gt;0.5$. While these measurements have revealed a number of key properties about the evolution of disc structure and kinematics, heterogeneous techniques and samples have led to disparate findings – especially when comparing different dynamical tracers (e.g. ${\rm H} \, \alpha$, [C ii], and CO). In this paper, we present a literature compilation of 233 disc galaxies with measurements of velocity dispersion and rotational velocity between $z=0.5 \!-\! 8$; a subset of 66 galaxies has measurements of molecular gas fractions. We explore the connection between disc velocity dispersion measurements over 8 Gyr as traced by multiple phases with the expectations from Toomre stability models. When sample properties are taken into account (e.g. stellar mass and tracer), there is little evolution in disc dispersions between $z\sim 1.5 \!-\! 8$, consistent with expectations from model assumptions. We find ionized gas dispersions are higher by ${\sim} 2$ times from molecular gas dispersions at a fixed gas mass. These results are sensitive to the molecular gas tracer, with results from [C ii] showing mixed behaviour indicative of its multiphase origin. The [C ii] kinematics can be reconciled with molecular and ionized gas tracers when star formation rates are taken into account.