A view of the M81 galaxy group via the H-alpha window

Abstract

We present images for 36 galaxies of the M81 group obtained in the H-alpha line. Estimates of the H-alpha flux and star formation rate, SFR, are avialable now for all the known members of the group with absolute magnitudes down to M_B = -10^m. The character of distribution of the galaxies over three paremeters: M_B, SFR, and total hydrogen mass permits us to draw the following conclusions as to evolution status of the group population. a) Spiral and irregular type galaxies would have time to generate their luminosity (baryon mass) during the cosmological time T_0=13.7 Gyr, but dwarf spheroidal objects are capable of reproducing only ~5% of their observed luminosity. b) S and Im, BCD galaxies possess the supply of gas sufficient to maintain their observed SFRs during only next (1/4 -1/3)T_0 years, while dIr and dSph populations have the mean gas depletion time about 3 T_0. c) There is indirect evidence that the star formation in Im, BCD and dIr galaxies proceeds in a mode of vigorous burst activity rather than in the form of a sluggish process. We note the dwarf tidal system near NGC 3077, the Garland, to have the highest SFR per unit luminosity among 150 galaxies of the Local volume with known SFRs. Being averaged over the local "cell of homogeneity" of 4 Mpc in diameter around M 81, the rate of star formation of the group, rho(SFR)= 0.165 M_sun/year*Mpc^3, proves to be 5-8 times higher than, that of the average global rate at Z =0.