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arXiv · 1004.1342

The Metal-Enriched Outer Disk of NGC 2915

Jessica K. Werk·Mary E. Putman·Gerhardt R. Meurer·David A. Thilker·Ronald J. Allen·Joss Bland-Hawthorn·Andrey V. Kravtsov·Kenneth C. Freeman
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Abstract

We present optical emission-line spectra for outlying HII regions in the extended neutral gas disk surrounding the blue compact dwarf galaxy NGC 2915. Using a combination of strong-line R23 and direct oxygen abundance measurements, we report a flat, possibly increasing, metallicity gradient out to 1.2 times the Holmberg radius. We find the outer-disk of NGC 2915 to be enriched to a metallicity of 0.4 Z_solar. An analysis of the metal yields shows that the outer disk of NGC 2915 is overabundant for its gas fraction, while the central star-foming core is similarly under-abundant for its gas fraction. Star formation rates derived from very deep ~14 ks GALEX FUV exposures indicate that the low-level of star formation observed at large radii is not sufficient to have produced the measured oxygen abundances at these galactocentric distances. We consider 3 plausible mechanisms that may explain the metal-enriched outer gaseous disk of NGC 2915: radial redistribution of centrally generated metals, strong galactic winds with subsequent fallback, and galaxy accretion. Our results have implications for the physical origin of the mass-metallicity relation for gas-rich dwarf galaxies.

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Jessica K. Werk, Mary E. Putman, Gerhardt R. Meurer, David A. Thilker, Ronald J. Allen, Joss Bland-Hawthorn, Andrey V. Kravtsov, Kenneth C. Freeman. 2010-04-08. The Metal-Enriched Outer Disk of NGC 2915. https://doi.org/10.1088/0004-637x%2F715%2F1%2F656

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