A Hubble Space Telescope Survey of the Host Galaxies of Superluminous
  Supernovae
  We present Hubble Space Telescope (HST) WFC3 UV and near-IR (nIR) imaging of
21 Superluminous Supernovae (SLSNe) host galaxies, providing a sensitive probe
of star formation and stellar mass with the hosts. Comparing the photometric
and morphological properties of these host galaxies with those of core collapse
supernovae (CCSNe) and long-duration gamma-ray bursts (LGRBs), we find SLSN
hosts are fainter and more compact at both UV and nIR wavelengths, in some
cases we barely recover hosts with absolute magnitude around MV ~ -14. With the
addition of ground based optical observations and archival results, we produce
spectral energy distribution (SED) fits to these hosts, and show that SLSN
hosts possess lower stellar mass and star formation rates. This is most
pronounced for the hydrogen deficient Type-I SLSN hosts, although Type-II
H-rich SLSN host galaxies remain distinct from the bulk of CCSNe, spanning a
remarkably broad range of absolute magnitudes, with ~30% of SLSNe-II arising
from galaxies fainter than Mn I R ~ -14. The detection of our faintest SLSN
hosts increases the confidence that SLSNe-I hosts are distinct from those of
LGRBs in star formation rate and stellar mass, and suggests that apparent
similarities in metallicity may be due to the limited fraction of hosts for
which emission line metallicity measurements are feasible. The broad range of
luminosities of SLSN-II hosts is difficult to describe by metallicity cuts, and
does not match the expectations of any reasonable UV-weighted luminosity
function, suggesting additional environmental constraints are likely necessary
to yield hydrogen rich SLSNe.
