The host galaxy of the super-luminous SN 2010gx and limits on explosive
  nickel-56 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] 4363 Angs 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 240-560 days
after explosion to search for any sign of radioactive nickel-56, which might
provide further insights on the explosion mechanism and the progenitor's
nature. We reach griz magnitudes of m_AB~26, but do not detect SN 2010gx at
these epochs. The limit implies that any nickel-56 production was similar to or
below that of SN 1998bw (a luminous type Ic SN that produced around 0.4 M_sun
of nickel-56). The low volumetric rates of these supernovae (~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_sun), high
progenitor mass (>60 M_sun) and high rotation rate (fastest 10% of rotators).
