RESOLVING IONIZATION AND METALLICITY ON PARSEC SCALES ACROSS MRK 71 WITH HST-WFC3

Blue compact dwarf (BCD) galaxies in the nearby universe provide a means for studying feedback mechanisms and star formation processes in low-metallicity environments in great detail. Owing to their vicinity, these local analogs to primordial young galaxies are well suited for high-resolution studies that are unfeasible for high-redshift galaxies. Here we present Hubble Space Telescope. Wide Field Camera 3 observations of one such BCD, Mrk. 71, one of the most powerful local starbursts known, in the light of [O II], HeII, H beta, [O III], H alpha, and [S II]. At D similar or equal to 3.44 Mpc, this extensive suite of emission-line images enables us to explore the chemical and physical conditions of Mrk. 71 on similar to 2 pc scales. We use emission-line diagnostics to distinguish ionization mechanisms on a pixel-by-pixel basis and show that despite the previously reported hypersonic gas and superbubble blowout, the gas in Mrk. 71 is photoionized, with no sign of shock-excited emission. He II emission line images are used to identify up to six Wolf-Rayet stars, three of which lie on the edge of a blowout region. Using strong-line metallicity diagnostics, we present the first "metallicity image" of a galaxy, revealing chemical inhomogeneity on scales of <50 pc. We additionally demonstrate that while chemical structure can be lost at large scales, metallicity diagnostics can break down on spatial scales smaller than an H II region. This study. highlights not only. the benefits of high-resolution spatially resolved observations in assessing the effects of feedback mechanisms. but also the potential limitations when employing emission-line diagnostics; these results are particularly relevant as we enter the era of extremely large telescopes.