Abstract:
Galaxy mass-metallicity (M-Z) relations provide important diagnostics to evaluate galaxy evolution over a wide range in masses to help discriminate among various models for the histories of galaxy assembly. While a variety of observational and theoretical studies have focused on M-Z relations for nearby and distant massive galaxies, the shapes of these relations can be anchored by similar M-Z relations for dwarf galaxies in the nearby universe, which provide "zero-points" at low-mass and low-redshift. The Spitzer Local Volume Legacy (LVL) survey has gathered homogeneous near- and mid-infrared fluxes of 258 galaxies in a volume-complete sample within 11 Mpc. For a subsample of 50 star-forming dwarf galaxies with well-measured gas-phase metallicities, we construct and examine optical and near-infrared luminosity-metallicity (L-Z) relations. We show that the slope of the L-Z relation varies little from the optical to near-infrared wavelengths, and the dispersion generally decreases with increasing wavelength. With a prescription to compute stellar masses, the resulting M-Z relation has slope consistent with predictions, although the slope is shallower than the slope for the relation derived for more massive galaxies. With their measured gas contents, dwarf galaxies follow chemical evolution tracks with effective yields in the range between 10 and 80% of the solar value, which suggests that dwarf galaxies experience some but not complete loss of their metals.