# Indiana University

 dc.contributor.author Berg, D.A. en dc.contributor.author Skillman, E.D. en dc.contributor.author Marble, A.R. en dc.contributor.author Van Zee, L. en dc.contributor.author Engelbracht, C.W. en dc.contributor.author Lee, J.C. en dc.contributor.author Kennicutt, R.C. en dc.contributor.author Calzetti, D. en dc.contributor.author Dale, D.A. en dc.contributor.author Johnson, B.D. en dc.date.accessioned 2014-11-03T18:42:05Z en dc.date.available 2014-11-03T18:42:05Z en dc.date.issued 2012 en dc.identifier.citation Berg, D. A., Skillman, E. D., Marble, A. R., Van Zee, L., Engelbracht, C. W., Lee, J. C., . . . Johnson, B. D. (2012). Direct oxygen abundances for low-luminosity LVL galaxies. Astrophysical Journal, 754(2), 98. http://dx.doi.org/10.1088/0004-637X/754/2/98 en dc.identifier.uri https://hdl.handle.net/2022/19103 dc.description.abstract We present MMT spectroscopic observations of H II regions in 42 low luminosity galaxies in the Spitzer Local Volume Legacy survey. For 31 of the 42 galaxies in our sample, we were able to measure the temperature sensitive [O III] $\lambda$4363 line at a strength of $4\sigma$ 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 $\mu$m 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 abundances 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 $\mu$m luminosity-metallicity relationships for the 38 objects were found to be$12 + log(O/H) = (6.27 \pm 0.21) + (- 0.11 \pm 0.01)M_{B}$and$12+log(O/H) = (6.10 \pm 0.21) + (- 0.10 \pm 0.01)M_{[4.5]}$with dispersions of $\sigma$ = 0.15 and 0.14, respectively. The slopes of the optical and near-IR L-Z relationships have been reported to be different for galaxies with luminosities greater than that of the LMC. However, the similarity of the slopes of the optical and near-IR L-Z relationships for our sample probably reflects little influence by dust extinction in the low luminosity galaxies. For this sample, we derive a mass-metallicity relationship of $12 + log\big(O/H\big) = \big(5.61 \pm 0.24\big) + \big(0.29 \pm 0.03\big)log \big(M_{\star}\big)$, which agrees with previous studies; however, the dispersion ($\sigma$ = 0.15) is not significantly lower than that of the L-Z relationships. Because of the low dispersions in these relationships, if an accurate distance is available, the luminosity of a low luminosity galaxy is often a better indicator of metallicity than that derived using certain "strong-line" methods, so significant departures from the L-Z relationships may indicate that caution is prudent in such cases. With these new "direct" metallicities we also revisit the 70/160 $\mu$m color metallicity relationship. Additionally, we examine N/O abundance trends with respect to oxygen abundance and B - V color. We find a positive correlation between N/O ratio and B - V color for $0.05 \lesssim B - V \lesssim 0.75: log (N/O) = (1.18 \pm 0.9\big) × (B - V) + (- 1.92 \pm 0.08)$, with a dispersion of $\sigma$ = 0.14, which is in agreement with previous studies. en dc.language.iso en_US en dc.publisher The American Astronomical Society en dc.relation.isversionof https://doi.org/10.1088/0004-637X/754/2/98 en dc.rights © 2012 The American Astronomical Society en dc.subject galaxies: abundances en dc.subject galaxies: dwarf en dc.subject galaxies: evolution en dc.title Direct oxygen abundances for low-luminosity LVL galaxies en dc.type Article en dc.altmetrics.display false en
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