X-rays from Blue Compact Dwarf Galaxies
  We measured the X-ray fluxes from an optically-selected sample of blue
compact dwarf galaxies (BCDs) with metallicities <0.07 and solar distances less
than 15 Mpc. Four X-ray point sources were observed in three galaxies, with
five galaxies having no detectable X-ray emission. Comparing X-ray luminosity
and star formation rate, we find that the total X-ray luminosity of the sample
is more than 10 times greater than expected if X-ray luminosity scales with
star formation rate according to the relation found for normal-metallicity
star-forming galaxies. However, due to the low number of sources detected, one
can exclude the hypothesis that the relation of the X-ray binaries to SFR in
low-metalicity BCDs is identical to that in normal galaxies only at the 96.6%
confidence level. It has recently been proposed that X-ray binaries were an
important source of heating and reionization of the intergalactic medium at the
epoch of reionization. If BCDs are analogs to unevolved galaxies in the early
universe, then enhanced X-ray binary production in BCDs would suggest an
enhanced impact of X-ray binaries on the early thermal history of the universe.
