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

Abstract

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 pspulation 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 108a; 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. K e y words: galaxies: NGC 2976 --stellar populations -dust A A A subject classification: 157 IntroductionThe population content of galaxies and its development with time has since long attracted considerable attention. T h e distribution (and kinematics) of stars of different age and of different metal content bears valuable information about the history of galaxy evolution. Observed intensity profiles of the old population, trends in the ellipticity of the isophotes, systematic variations of metallicity and colours can be compared with predictions from evolutionary models t o get insight into the past history of the systems (for instance Larson 1975, Larson and Tinsley 1978, Arimoto and Yoshii 1986, 1987, Katz and Gunn 1991. The occurence and the distribution of young stars and their relation to the interstellar gas and dust are indicative of the processes which trigger star formation. Irregularities in the distribution of stars and interstellar matter may be signatures of recent interactions with neighbouring systems. Since every galaxy has its special history determined by environmental and initial conditions, discussion of individual galaxies is of its own value and is supplementary to the observation of selected parameters of a great number of objects for statistical discussion. Our interest in NGC 2976 is twofold. First, this Sc(pec) galaxy (de Vaucouleurs et al. 1976) is a member of the M81/M82 group of galaxies. It contains a large number of young concentrated star forming regions in its inner disk; many of them are conspicuous Ha-regions (Hodge and Kennicut 1983). T w o other members of this group, NGC 3077 and M82, suffered close encounters with M81 during the last 109a (for instance Cottrell 1977, Kilian 1980, Brouillet et al. 1991a. A huge cloud of interstellar matter, now enshrouding these galaxies, was probably generated by these events. A faint extension of the cloud links NGC 2976 t o the central group (Appleton et al. 1981(Appleton e...

The Advanced Camera for Surveys Nearby Galaxy Survey Treasury. Iv. The Star Formation History of NGC 2976

“…It is possible that the old stars are dominated by a spheroidal component of the galaxy (Bronkalla et al 1992) and only the young stars are truly sampling the disk. Alternatively, the old stars may simply be a well-mixed old disk population.…”

H kinematics of the SINGS nearby galaxies survey -- I

“…Stil & Israel (2002) observed that in H I the rotation curve seems to flatten near the edge of the H I disc. According to Bronkalla, Notni & Mutter (1992), the outer parts of NGC 2976 have been undisturbed for a long time and are very old (5 Gy, probably up to 15 Gy).…”

Magnetic fields and star formation in low-mass Magellanic-type and peculiar galaxies

“…The magnetic field B-vectors can be seen outside the galactic disc as parallel to its southern edge. Since the outer parts of NGC 2976 were probably undisturbed for a long time (Bronkalla et al 1992), this configuration of the ordered field can indicate that the magnetic field was stretched or compressed by external forces acting long ago. We will analyse higher resolution VLA data for this galaxy in a future paper (Drzazga et al, in prep.…”