Galaxies with Abnormally High Gas Content in the Disk by Anatoly. V. Zasov et al. on Monday 28 November

The content of gas in galaxies with an anomalously high relative mass of

hydrogen $M_{HI}/M_*$ for a given mass of the stellar population $M_*$

(VHR-galaxies) is considered, using the available samples of such galaxies. It

is shown that, within the optical diameter $D_{25}$, the mass of HI in VHR

galaxies, as well as in galaxies with "normal" HI content, is limited by a

value that depends on the specific angular momentum of the disk. Outer gaseous

disks beyond $D_{25}$, which contain the main amount of HI in most of the

galaxies we consider, are gravitationally stable, and, as a rule, they retain

an approximately constant value of the stability parameter $Q_{gas}$ over a

large range of radial distances. It allows to propose that the outer disks of

VHR galaxies are not recently acquired, but are of great age, and their

gravitational instability was the main regulator of star formation during their

formation. In this case, the extended disks of galaxies should also include a

low-brightness stellar components of old stars extending far beyond their

optical diameter $D_{25}$.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.14001v1