THE HOST GALAXY OF THE SUPER-LUMINOUS SN 2010gx AND LIMITS ON EXPLOSIVE 56Ni PRODUCTION

Super-luminous supernovae have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. While these extremely luminous explosions have been observed from z = 0.1 to 1.55, the closest explosions allow more detailed investigations of their host galaxies. We present a detailed analysis of the host galaxy of SN 2010gx (z = 0.23), one of the best studied super-luminous type Ic supernovae. The host is a dwarf galaxy (M-g = -17.42 +/- 0.17) with a high specific star formation rate. It has a remarkably low metallicity of 12 + log (O/H) = 7.5 +/- 0.1 dex as determined from the detection of the [OIII] lambda 4363 line. This is the first reliable metallicity determination of a super-luminous stripped-envelope supernova host. We collected deep multi-epoch imaging with Gemini + GMOS between 240 and 560 days after explosion to search for any sign of radioactive Ni-56, which might provide further insights on the explosion mechanism and the progenitor's nature. We reach griz magnitudes of m(AB) similar to 26, but do not detect SN 2010gx at these epochs. The limit implies that any Ni-56 production was similar to or below that of SN 1998bw (a luminous type Ic SN that produced around 0.4 M-circle dot of Ni-56). The low volumetric rates of these supernovae (similar to 10(-4) of the core-collapse population) could be qualitatively matched if the explosion mechanism requires a combination of low-metallicity (below 0.2 Z(circle dot)), high progenitor mass (>60 M-circle dot) and high rotation rate (fastest 10% of rotators).