Are the kinematics of DLAs in agreement with their arising in the gas disks of galaxies?

TL;DR

This paper shows that the gas kinematics in high-redshift Damped Ly Alpha systems do not match those of local galaxy disks, suggesting they originate from more dynamic, interaction-related gas rather than stable rotating disks.

Contribution

It provides a comparative analysis of gas kinematics in local galaxies and high-redshift DLAs, highlighting the role of non-rotational gas processes in DLAs.

Findings

Median velocity width of local HI gas is ~30 km/s.

DLA velocity widths are about twice as high as local HI gas.

Gas in high-redshift DLAs likely influenced by galaxy interactions and outflows.

Abstract

We demonstrate in this paper that the velocity widths of the neutral gas in Damped Ly Alpha (DLA) systems are inconsistent with these systems originating in gas disks of galaxies similar to those seen in the local Universe. We examine the gas kinematics of local galaxies using the high quality HI 21-cm data from the HI Nearby Galaxies Survey (THINGS) and make a comparison with the velocity profiles measured in the low-ionization metal lines observed in DLAs at high redshifts. The median velocity width of z=0 HI gas above the DLA column density limit of N=2x10^20 cm-2 is approximately 30 km/s, whereas the typical value in DLAs is a factor of two higher. We argue that the gas kinematics at higher redshifts are increasingly influenced by gas that is not participating in ordered rotation in cold disks, but is more likely associated with tidal gas related to galaxy interactions or processes such as superwinds and outflows. An analysis of the HI in the local interacting star-burst galaxy M82 shows that the velocity widths in this galaxy are indeed similar to what is seen in DLAs.