2025A&A...693A..91L

The gas dynamics of galaxies provide critical insights into the evolution of both baryons and dark matter (DM) across cosmic time. In this context, galaxies at cosmic noon, that is, in the period characterized by the most intense star formation and black hole activities, are particularly significant. We present an analysis of the gas dynamics of PKS 0529-549. This galaxy lies at z ≃ 2.6 and hosts a radio-loud active galactic nucleus (AGN). We used new ALMA observations of the [C I] (2-1) line at a spatial resolution of 0.18″ (∼1.5 kpc). We found that (1) the molecular gas forms a rotation-supported disk with V_rot/σ_v = 6 ± 3 and displays a flat rotation curve out to 3.3 kpc; (2) there are several noncircular components, including a kinematically anomalous structure near the galaxy center, a gas tail to the southwest, and possibly a second weaker tail to the east; and finally, (3) the dynamical estimates of the gas and stellar masses from fitting the rotation curve are inconsistent with photometric estimates made using standard gas conversion factors and stellar population models, respectively. These discrepancies may be due to systematic uncertainties in the photometric masses or in the dynamical masses, or they might be caused by a more massive radio-loud AGN-host galaxy that is hidden behind the gas-rich [C I] emitting starburst galaxy along the line of sight. Our work shows that in-depth investigations of 3D line cubes are crucial for revealing the complexity of gas dynamics in high-z galaxies, in which regular rotation may coexist with noncircular motions and possibly tidal structures.