NOEMA Observations of a Molecular Cloud in the low-metallicity Galaxy
  Kiso 5639
  A giant star-forming region in a metal-poor dwarf galaxy has been observed in
optical lines with the 10-m Gran Telescopio Canarias and in the emission line
of CO(1-0) with the NOEMA mm-wave interferometer. The metallicity was
determined to be 12+log(O/H)=7.83+-0.09, from which we estimate a conversion
factor of alpha_CO~100 Msun/pc2/(K km/s) and a molecular cloud mass of
~2.9x10^7 Msun. This is an enormous concentration of molecular mass at one end
of a small galaxy, suggesting a recent accretion. The molecular cloud
properties seem normal: the surface density, 120 Msun/pc2, is comparable to
that of a standard giant molecular cloud, the cloud's virial ratio of ~1.8 is
in the star-formation range, and the gas consumption time, 0.5 Gyr, at the
present star formation rate is typical for molecular regions. The low
metallicity implies that the cloud has an average visual extinction of only 0.8
mag, which is close to the threshold for molecule formation. With such an
extinction threshold, molecular clouds in metal-poor regions should have high
surface densities and high internal pressures. If high pressure is associated
with the formation of massive clusters, then metal-poor galaxies such as dwarfs
in the early universe could have been the hosts of metal-poor globular
clusters.
