difference from the isolated systems. Anyway, pair, group and cluster membership is not always connected with the stellar velocity dispersion exceeding the level needed for marginal gravitational stability. It seems that only a strong gravitation perturbation can be a cause of disk dynamical overheating. This conclusion also follows, for example, from the higher mean thickness of stellar disks in interacting edge-on galaxies (Reshetnikov, Combes (1997)).

The position of our Galaxy in the diagrams is shown by the open circle. For our Galaxy $(M/L_B)_d$ ratio was calculated using the local values of surface density and brightness measured for solar vicinity and accepting $h=3$ kpc. The surface brightness data in $B$-band was taken from Portinari et al. (2005).. Note, that the value of surface density in the Solar neighborhood obtained on the basis of marginal stability condition is in a good agreement with the direct estimates (Korchagin et al. (2003), Holmberg, Flynn (2004), Kuijken, Gilmore (1991)). This gives evidences of marginal stability of disk of Galaxy at least at the galactocentric distance of a few radial scalelenghts. This conclusion conforms with the idea of the absence of major merger events in the history of our Galaxy (see e.g. Wyse, 2009)).

In Fig. 