SUITES OF DWARFS AROUND NEARBY GIANT GALAXIES

Abstract

We consider a sample of the Updated Nearby Galaxy Catalog that contains eight hundred objects within 11 Mpc. Environment of each galaxy was characterized by a tidal index $\Theta_1$ depending on the separation and mass of the galaxy's Main Disturber (=MD). We ascribed the UNGC galaxies with a common MD to its suite, and ranked suite members according to their $\Theta_1$. All suite members with positive $\Theta_1$ are assumed to be physical companions of the MD. The distribution of suites by the number of members, n, follows to a relation $N(n) \sim n^{-2}$. The twenty most populated suites contain 468 galaxies, i.e. 59% of the UNGC sample. About 58% of our sample are members of physical groups. The fraction of MDs among the brightest galaxies is almost 100% and drops to 50% at $M_B = -18^m$. We discuss various properties of MDs, as well as galaxies belonging to their suites. The suite abundance practically does not depend on morphological type, linear diameter or hydrogen mass of MD, revealing the tightest correlation with the MD dynamical mass. Dwarf galaxies around MDs exhibit well-known segregation effects: the members of outskirts have later morphological types, richer HI-contents and higher rates of star formation activity. Nevertheless, there are some intriguing cases when dwarf spheroidal galaxies occur at the far periphery of the suites, as well as some late-type dwarfs residing close to MDs. The multiplicity of nearby groups according to number of their physical members can be described by the Hirsh-like index $h_g = 9$, indicating that the Local Volume contains 9 groups with populations exceeding 9 members. (abridged)