Bending instability in galaxies: the stellar disk thickness and the mass of spheroidal component

We present results of numerical N-body simulations of a galactic stellar disk embedded into a spherical dark halo. The non-linear dynamics of bending instabilities developing in the disk is studied. The bending modes, axisymmetric and not, are considered as main factors increasing the disk thickness. The relation between the disk vertical scale height and the halo+bulge-to-disk mass ratio is inferred. The method of estimation of the spherical-to-disk mass ratio for edgeon spiral galaxies based on this relation is studied and applied to constrain the spherical subsystem mass and the mass of dark halos (Mh/Md) in seven edge-on galaxies. The values of Mh/Md are of order 1 for our galaxies. Subject headings: edge-on galaxies, bending instability, halo, N-body simulations, galactic structure Sternberg Astronomical Institute, Moscow, 119899, Russia Volgograd State University, Volgograd, 400062, Russia Physics Department, University of Texas at El Paso, TX, USA