  The results of the stellar photometry of the images ACS/WFC and WFPC2 of the
HST are used to study stellar population and spatial distribution of stars in
three edge-on galaxies: NGC 891, NGC 4144 and NGC 4244. The measuring of the
number density of the old stars revealed two stellar substructures in these
galaxies: thick disk and halo. The borders of these substructures consisting
mainly of red giants, are determined by the change of number density gradient
of the old stars. The revealed halos have flattened shapes and extend up to 25
kpc from the galaxy planes. The obtained results of number density
distributions of different type stars perpendicular to the galaxy planes allow
us to verify our stellar model of spiral galaxies. Using the determination of
the tip of red giant branch (TRGB method) we have derived the following
distances: D = 9.82 Mpc (NGC 891), D = 7.24 Mpc (NGC 4144), D = 4.29 Mpc (NGC
4244).
