Companions around the nearest luminous galaxies: segregation and
  selection effects
  Using the "Updated Nearby Galaxy Catalog", we consider different properties
of companion galaxies around luminous hosts in the Local Volume. The data on
stellar masses, linear diameters,surface brightnesses, HI-richness, specific
star formation rate (sSFR), and morphological types are discussed for members
of the nearest groups, including the Milky Way and M 31 groups, as a function
of their separation from the hosts. Companion galaxies in groups tend to have
lower stellar masses, smaller linear diameters and fainter mean surface
brightnesses as the distance to their host decreases. The hydrogen-to-stellar
mass ratio of the companions increases with their linear projected separation
from the dominant luminous galaxy. This tendency is more expressed around the
bulge-dominated hosts. While linear separation of the companions decreases,
their mean sSFR becomes lower, accompanied with the increasing sSFR scatter.
Typical linear projected separation of dSphs around the bulge-dominated hosts,
350 kpc, is substantially larger than that around the disk-dominated ones, 130
kpc. This difference probably indicates the presence of larger hot/warm gas
haloes around the early-type host galaxies. The mean fraction of dSph
(quenched) companions in 11 the nearest groups as a function of their projected
separation R_p can be expressed as f(E) = 0.55 - 0.69 x R_p. The fraction of
dSphs around the Milky Way and M 31 looks much higher than in other nearby
groups because the quenching efficiency dramatically increases towards the
ultra-low mass companions. We emphasize that the observed properties of the
Local Group are not typical for other groups in the Local Volume due to the
role of selection effects caused by our location inside the Local Group.
