Reconciling the GRB rate and star formation histories
  While there are numerous indications that GRBs arise from the death of
massive stars, the GRB rate does not follow the global cosmic star formation
rate and, within their hosts, GRBs are more concentrated in regions of very
high star formation. We explain both puzzles here. Using the publicly available
VESPA database of SDSS Data Release 7 spectra, we explore a multi-parameter
space in galaxy properties, like stellar mass, metallicity, dust etc. to find
the sub-set of galaxies that reproduce the recently obtained GRB rate by
Wanderman & Piran (2010). We find that only galaxies with present stellar
masses below < 10^{10} Msun and low metallicity reproduce the observed GRB
rate. This is consistent with direct observations of GRB hosts and provides an
independent confirmation of the nature of GRB hosts. Because of the
significantly larger sample of SDSS galaxies, we compute their correlation
function and show that they are anti-biased with respect to the dark matter:
they are in filaments and voids. Using recent observations of massive stars in
local dwarfs we show how the fact that GRB hosts galaxies are dwarfs can
explain the observation that GRBs are more concentrated in regions of high star
formation than SNe. Finally we explain these results using new theoretical
advances in the field of star formation.
