SDSS 0809+1729: Connections Between Extremely Metal-Poor Galaxies and Gamma-Ray Burst Hosts

Abstract

We discuss the serendipitous discovery of an extremely metal-poor galaxy, SDSS 0809+1729, classified as a star in the Sloan Digital Sky Survey (SDSS). The galaxy has a redshift z=0.0441 and a B-band absolute magnitude M B =-17.1. With a metallicity of log(O/H)+12~7.44 or ~1/20 solar, this galaxy is among the 10 most metal-poor emission-line galaxies known. SDSS 0809+1729 is a blue compact galaxy (BCG) with a stellar age of ~4.5 Myr, a star formation rate of 0.18 M solar yr -1, and a large gas-phase electron density (~367 cm -3). Similar values of these parameters are common among other extremely metal-poor galaxies, including I Zw 18. SDSS 0809+1729 is, however, unusual among BCGs because it lies in the same region of the luminosity-metallicity diagram as the two lowest metallicity long-duration gamma-ray burst (GRB) hosts. For a given B-band luminosity, both nearby GRB hosts and SDSS 0809+1729 have systematically lower metallicities than dwarf irregulars, the majority of BCGs, and normal star-forming galaxies. Because the star formation properties of SDSS 0809+1729 are similar to nearby long-duration GRB hosts, SDSS 0809+1729 may be a potential GRB host. Identification of larger samples of similar extremely metal-poor objects may provide important insights into the conditions required to produce long-duration GRBs.