ALMA observations of cool dust in a low-metallicity starburst,
  SBS0335-052
  We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 Band 7
observations of an extremely metal-poor dwarf starburst galaxy in the Local
Universe, SBS0335-052 (12+log(O/H)~7.2). With these observations, dust is
detected at 870micron (ALMA Band 7), but 87% of the flux in this band is due to
free-free emission from the starburst. We have compiled a spectral energy
distribution (SED) of SBS0335-052 that spans almost 6 orders of magnitude in
wavelength and fit it with a spherical dust shell heated by a single-age
stellar population; the best-fit model gives a dust mass of (3.8+/-0.6)x10^4
Msun. We have also constructed a SED including Herschel archival data for
IZw18, another low-metallicity dwarf starburst (12+log(O/H)=7.17), and fit it
with a similar model to obtain a dust mass of (3.4+/-1.0)x10^2 Msun. Compared
with their atomic gas mass, the dust mass of SBS0335-052 far exceeds the
prediction of a linear trend of dust-to-gas mass ratio with metallicity, while
IZw18 falls far below. We use gas scaling relations to assess a putative
missing gas component in both galaxies and find that the missing, possibly
molecular, gas in SBS0335-052 is a factor of 6 times higher than the value
inferred from the observed HI column density; in IZw18 the missing component is
4 times smaller. Ultimately, despite their similarly low metallicity, the
differences in gas and dust column densities in SBS0335-052 and IZw18 suggest
that metal abundance does not uniquely define star-formation processes. At some
level, self-shielding and the survival of molecules may depend just as much on
gas and dust column density as on metallicity. The effects of low metallicity
may at least be partially compensated for by large column densities in the
interstellar medium.
