Dust Extinction and Metallicities of Star-Forming Lyman Alpha Emitting Galaxies at Low Redshift

TL;DR

This study analyzes low-redshift Lyman alpha emitting galaxies, revealing their dust extinction levels, metallicities, and stellar populations, and compares these properties to other star-forming galaxies at similar redshifts.

Contribution

It provides new insights into the dust, metallicity, and stellar ages of low-redshift LAEs, highlighting their lower metallicities compared to typical galaxies at the same epoch.

Findings

Most galaxies have metallicity Z < 0.4 Z_sun.

Dust extinction is similar to high-redshift LAEs with Av ~ 0.3 mag.

LAEs are systematically more metal-poor than other star-forming galaxies at similar stellar masses.

Abstract

We present the results of an optical spectroscopic study of 12 GALEX-discovered star-forming Lyman alpha 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 AGNs lowers the typical stellar population age and stellar mass of this sample to ~ 300 Myr and ~ 4 x 10^9 Msol, 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 many high-redshift LAEs. Comparing the ratio of Lyalpha/Halpha and the Lyman alpha equivalent widths to the measured dust extinction, we find that the ISMs in these objects appear to be neither enhancing nor seriously attenuating the Lyman alpha 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 Zsol. We find that at a fixed stellar mass, these low-redshift LAE analogs are offset by ~ 0.6 dex lower in metallicity from the general galaxy population at similar redshifts based on the local mass-metallicity relationship. This implies that galaxies with Lyman alpha 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.