that both numerical simulations (Sotnikova, Rodionov (2006), Khoperskov et al. (2010)) and the analysis of observations of edge-on galaxies (Mosenkov et al. (2010), Bizyaev, Mitronova (2009), Bizyaev (2010)) show that this correlation is rather sparse especially for galaxies with small bulges. Moreover, numerical dynamical models by far are not always compatible with the assumption of disk marginal stability (see, e.g., Zasov et al. (2008)).

A difficulty of estimation of the ratio of observed velocity dispersion $c_{obs}$ to its critical value $(c_r)_{cr}$ lies first of all in the difficulty of measurement of $c_{obs}$ at sufficiently large galactocentric distances and in addition is due to a number of factors hard to be taken into account even in the axissymmetrical galaxy model. Among the latter factors are the variation of critical Toomre parameter with radius, the ratio of radial to vertical velocity dispersion and the account of asymmetric drift in the estimation of disk angular velocity especially for the early type galaxies.

The main goal of this work is to find out how far the observed values of velocity dispersion at given $R$ are from the expected ones for marginally stable disks for different type galaxies. For this purpose, we analyze the velocity 