2024MNRAS.533.1321N

The circumgalactic medium (CGM) hosts many physical processes with different kinematic signatures that affect galaxy evolution. We address the CGM-galaxy kinematic connection by quantifying the fraction of H I that is aligned with galaxy rotation with the equivalent width co-rotation fraction, $f_{\rm EWcorot}$. Using 70 quasar sightlines having Hubble Space Telescope/Cosmic Origins Spectrograph H I absorption (${12\lt \log (N(\rm{{\rm H}\,{\small I}})/{\rm cm}^{-2})\lt 20}$) within $5R_{\rm vir}$ of $z\lt 0.6$ galaxies we find that $f_{\rm EWcorot}$ increases with increasing H I column density. $f_{\rm EWcorot}$ is flat at $\sim 0.6$ within $R_{\rm vir}$ and decreases beyond $R_{\rm vir}$ to $f_{\rm EWcorot}$$\sim 0.35$. $f_{\rm EWcorot}$ also has a flat distribution with azimuthal and inclination angles within $R_{\rm vir}$, but decreases by a factor of two outside of $R_{\rm vir}$ for minor axis gas and by a factor of 2 for edge-on galaxies. Inside $R_{\rm vir}$, co-rotation dominated H I is located within $\sim 20$ deg of the major and minor axes. We surprisingly find equal amounts of H I absorption consistent with co-rotation along both major and minor axes within $R_{\rm vir}$. However, this co-rotation disappears along the minor axis beyond $R_{\rm vir}$, suggesting that if this gas is from outflows, then it is bound to galaxies. $f_{\rm EWcorot}$ is constant over two decades of halo mass, with no decrease for log(M$_{\rm h}/{\rm M}_{\odot })\gt 12$ as expected from simulations. Our results suggest that co-rotating gas flows are best found by searching for higher column density gas within $R_{\rm vir}$ and near the major and minor axes.