The Metal-Enriched Outer Disk of NGC 2915
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.
Keywords
Cite
@article{arxiv.1004.1342,
title = {The Metal-Enriched Outer Disk of NGC 2915},
author = {Jessica K. Werk and Mary E. Putman and Gerhardt R. Meurer and David A. Thilker and Ronald J. Allen and Joss Bland-Hawthorn and Andrey V. Kravtsov and Kenneth C. Freeman},
journal= {arXiv preprint arXiv:1004.1342},
year = {2015}
}
Comments
11 pages, 4 figures, accepted to ApJ April 8th, 2010