HI content in galactic disks: The role of gravitational instability

• Published in: Astronomy letters 2017-07, Vol.43 (7), p.439-451
• Main Authors: Zasov, A. V., Zaitseva, N. A.
• Format: Article
• Language: English
• Subjects: Accretion disks; Angular momentum; Astronomy; Astrophysics; Astrophysics and Astroparticles; Brightness; Deposition; Galactic disk; Galactic rotation; Galaxies; Gravitation; Gravitational instability; Gravitational waves; Hydrogen; Hydrogen storage; Instability; Observations and Techniques; Physics; Physics and Astronomy; Star & galaxy formation; Star formation; Stars; Stellar rotation
• ISSN: 1063-7737; 1562-6873
• DOI: 10.1134/S1063773717070052

We examine the dependence of the total hydrogen mass M HI in late-type star-forming galaxies on rotation velocity V rot and optical size D 25 or radial scale length R 0 of the disk for two samples of galaxies: (i) isolated galaxies (AMIGA) and (ii) galaxies with edge-on disks (flat galaxies according to Karachentsev et al.). M HI given in the HYPERLEDA database for flat galaxies have turned out to be, on average, overestimated by ~0.2 dex compared to isolated galaxies with similar V rot or D 25 , which is apparently due to an overestimation of the self-absorption in the HI line. The hydrogen mass in the galaxies of both samples closely correlates with the total specific angular momentum of the galactic disk J , which is proportional to V rot D 25 or V rot R 0 , with the low-surface-brightness galaxies lying along the common V rot R 0 sequence. We discuss the possibility of explaining the relationship between M HI and V rot D 25 by assuming that the gas mass in the disk is regulated by the marginal gravitational stability condition for the gas layer. Comparison of the observed and theoretically expected dependences leads us to conclude that either the gravitational stability corresponds to higher values of the Toomre parameter than is usually assumed, or the threshold stability condition formost galaxies was fulfilled only in the past, when the gasmass in the disks was a factor of 2–4 higher than that at present (except for the galaxies with an anomalously high observed HI content). The latter condition requires that for most galaxies the conversion of gas into stars be not compensated by the external accretion of gas onto the disk.