DUST EXTINCTION AND METALLICITIES OF STAR-FORMING Lyα EMITTING GALAXIES AT LOW REDSHIFT*
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We present the results of an optical spectroscopic study of 12 GALEX-discovered star-forming Lyα emitting galaxies (LAEs) at z ∼ 0.3. We measure the emission-line fluxes from these galaxies by fitting their observed spectra to stellar population models in order to correct for underlying stellar absorption. We revisit earlier stellar population model fitting results, finding that excluding now-known active galactic nuclei lowers the typical stellar population age and stellar mass of this sample to ∼ 300 Myr and 4 × 109M⊙, respectively. We calculate their dust extinction using the Balmer decrement, and find a typical visual attenuation of AV 0.3 mag, similar to that seen in some high-redshift LAEs. Comparing the ratios of Lyα/Hα and the Lyα equivalent widths to the measured dust extinction, we find that the interstellar media (ISMs) in these objects appear to be neither enhancing nor seriously attenuatingthe Lyα equivalent widths, as would be the case in a quasi-clumpy ISM. Lastly, we perform a detailed analysis of the gas-phase metallicities of these galaxies, and we find that most galaxies in our sample have Z ≲0.4 Z⊙. We find that at a fixed stellar mass, these low-redshift LAE analogs are offset by 0.3-0.6 dex lower metallicity from the general galaxy population at similar redshifts based on the local mass-metallicity relationship. This implies that galaxies with Lyα in emission may be systematically more metal-poor than star-forming galaxies at the same stellar mass and redshift, similar to preliminary results at z ∼ 2. © 2011. The American Astronomical Society. All rights reserved.
author list (cited authors)
Finkelstein, S. L., Cohen, S. H., Moustakas, J., Malhotra, S., Rhoads, J. E., & Papovich, C.