Direct Oxygen Abundances for Low-Luminosity LVL Galaxies

We present MMT spectroscopic observations of H II regions in 42 low luminosity galaxies in the Spitzer Local Volume Legacy (LVL) survey. For 31 of the 42 galaxies in our sample, we were able to measure the temperature sensitive O III λ4363 line at a strength of 4σ or greater, and thus determine oxygen abundances using the “direct” method. Our results provide the first “direct ” estimates of oxygen abundance for 19 of these galaxies. “Direct ” oxygen abundances were compared to B-band luminosities, 4.5 µm luminosities, and stellar masses in order to characterize the luminosity-metallicity and mass-metallicity relationships at low-luminosity. We present and analyze a “Combined Select ” sample composed of 38 objects (drawn from a sub-set of our parent sample and the literature) with “direct ” oxygen abun-dances and reliable distance determinations (based on the tip of the red giant branch or Cepheid variables). Consistent with previous studies, the B-band and 4.5 µm luminosity-metallicity relationships for the 38 objects were found to be 12 + log(O/H) =