Science Highlight: All quiet at z=4.5

Standard galaxy formation models expect that young galaxies should be highly turbulent and kinematically chaotic, as a result of violent gas accretion and frequent mergers. Observations appear to tell a very different story. In this paper, Roman-Oliveira (Kapteyn Institute), Fraternali and Rizzo (2023, MNRAS 521, 1045) show archival ALMA data of the [C II] 158 micron line of five galaxies at z ~ 4.5 at 0.1-0.2 arcsec resolution (~1 kpc). All these galaxies show clear velocity gradients in the [C II] line. Four of these can be explained as rotationally supported disk, and only one is a likely unresolved merger. Turbulent velocities are low, showing that quiescent disks are common even at z ~ 4.5. This paper also shows that the high resolutions offered by ALMA are essential to separate the quiescent disks from localized kinematic features such as inflow/outflow. It also illustrates the potential for discovery through publicly accessible ALMA archival data, even for previously published data that were never interpreted together.


Figure: Observed and modeled velocity patterns of ALMA archival [C II] line emission of the five galaxies at z~4.5 studied by Roman-Oliveira et al. (2023).