6 HI mass and angular momentum

For the disks of gas-rich galaxies, where the active star formation is going on, the amount of hydrogen mass and angular momentum, proportional to ($V_{\rm m}\cdot A_{25})$, must follow a linear regression: $M_{\rm HI}\propto V_{\rm m} A_{25}$ [29, (Zasov 1974).] For 134 spiral galaxies [30, Zasov & Rubtzova (1989)] derived a relation ${\rm log}M_{\rm HI}\propto(1.3\pm0.1){\rm log}(V_{\rm m}\cdot A_{25})$. Considering a sample of 535 thin (buldgeless) edge-on galaxies [14, Karachentsev et al. (1999)] found that the slope of this relation is close to unity, $k = 1.08\pm0.03$, in the range of angular momentum covering two orders.

 

Figure 9: The HI mass as a function of angular momentum represented by a product of rotational velocity of the galaxy on its standard linear diameter. The solid line shows the least-squares regression. The quantities "r" and "k" in a corner correspond to the regression parameters in the Cols. (4) and (7) of Table 1

Figure 9 shows the relation between hydrogen mass and angular momentum for the LV galaxies. Because of the presence of a large number of small nearby galaxies, the range of their angular momentum extends over three orders. In this wide range the relation has a slope $k = 0.99\pm0.04$, correlation coefficient r = 0.89, and the standard deviation $\sigma({\rm log}M_{\rm HI})= 0.36$.Therefore, we may consider that the gaseous disks of giant spiral galaxies as well as dwarf irregular ones are situated, apparently, near the threshold of gravitational instability, favouring active star formation in them.