SDSS 0809+1729: Connections between extremely metal-poor galaxies and gamma-ray burst hosts

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 similar to 7.44 or similar to 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 similar to 4.5 Myr, a star formation rate of 0.18 M-circle dot yr(-1), and a large gas-phase electron density (similar to 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.