Stellar populations and dust in the galaxy NGC 2976, a low-luminosity member of the M81 group

Photographic UBV photometry of NGC 2976, a low-luminosity member of the central M81 group of galaxies, is presented. Young stars in the central disk determine the optical view and the classification of this Sc(pec) galaxy. It is surrounded by a halo of an old population which contains nearly all the mass and half the luminosity of the system. This halo has some properties typical of spheroidal dwarf galaxies: an exponential brightness profile, an ellipticity trend of the isophotes typical of low-mass systems, and mass and luminosity near the upper limit of typical dwarfs. In the central population I disk, star formation proceeds in dense associations scattered irregularly in a broad ringlike region of 1.2 kpc radius just inside the turnover of the rotation curve. This star formation episode may last since some 10⁸ a; it is possibly triggered by gas infall from the interstellar cloud generated during encounters between other group members in the central M81 group. A direct triggering by recent encounters is excluded since NGC 2976 is undisturbed in its outer parts.