Slow Cooling in Low Metallicity Clouds: An Origin of Globular Cluster
  Bimodality?
  We explore the relative role of small-scale fragmentation and global collapse
in low-metallicity clouds, pointing out that in such clouds the cooling time
may be longer than the dynamical time, allowing the cloud to collapse globally
before it can fragment. This, we suggest, may help to explain the formation of
the low-metallicity globular cluster population, since such dense stellar
systems need a large amount of gas to be collected in a small region (without
significant feedback during the collapse). To explore this further, we carry
out numerical simulations of low-metallicity Bonner-Ebert stable gas clouds,
demonstrating that there exists a critical metallicity (between 0.001 and 0.01
$Z_\odot$) below which the cloud collapses globally without fragmentation. We
also run simulations including a background radiative heating source, showing
that this can also produce clouds that do not fragment, and that the critical
metallicity -- which can exceed the no-radiation case -- increases with the
heating rate.
