Comparing molecular gas across cosmic time-scales: the Milky Way as both
  a typical spiral galaxy and a high-redshift galaxy analogue
  Detailed observations of the nearest star-forming regions in the Milky Way
(MW) provide the ultimate benchmark for studying star formation. The extent to
which the results of these Galaxy-based studies can be extrapolated to
extragalactic systems depends on the overlap of the environmental conditions
probed. In this paper, we compare the properties of clouds and star-forming
regions in the MW with those in nearby galaxies and in the high-redshift
Universe. We find that in terms of their baryonic composition, kinematics, and
densities, the clouds in the solar neighbourhood are similar to those in nearby
galaxies. The clouds and regions in the Central Molecular Zone (CMZ, i.e. the
inner 250 pc) of the MW are indistinguishable from high-redshift clouds and
galaxies. The presently low star formation rate in the CMZ therefore implies
that either (1) its gas represents the initial conditions for high-redshift
starbursts or (2) some yet unidentified process consistently suppresses star
formation over >100 Myr time-scales. We conclude that the MW contains large
reservoirs of gas with properties directly comparable to most of the known
range of star formation environments and is therefore an excellent template for
studying star formation across cosmological time-scales.
