Masses of Isolated Spiral KIG Galaxies, Determined by the Motions of Their Faint Companions

We have updated the classification of late-type galaxies presented in the Catalog of Isolated Galaxies (KIG) using the advanced digital sky surveys. Our search for companions around 959 KIG galaxies revealed 141 neighbors associated with 111 KIG galaxies within the mutual projection separation of less than 330 kpc and the radial velocity difference not exceeding 500 km s –1 . Typical luminosity of the companions turned out to be weaker than the luminosity of the main galaxies by more than an order of magnitude. Considering these small companions as test particles that move around the KIG galaxies along the Keplerian orbits with eccentricity of e ≃ 0.7, we estimated the total (orbital) masses of spiral KIG galaxies. Their average orbital mass-to- K -band luminosity ratio, (20.9 ± 3.1)M_⊙/L_⊙, is in a good agreement with the corresponding value for the nearby Milky Way, M 31 and M 81-type massive spirals. Isolated disk-shaped galaxies have an on the average 2–3 times smaller total-mass-to-stellar-mass ratio than those of isolated bulge-shaped galaxies.