  Constraints on the molecular gas content of galaxies at high redshift are
crucial to further our understanding of star formation and galaxy evolution
through cosmic times, as molecular gas is the fuel for star formation. Since
its initial detection at large cosmic distances almost two decades ago, studies
of molecular gas in the early universe have come a long way. We have detected
CO emission from >100 galaxies, covering a range of galaxy populations at z>1,
reaching out to z>6, down to sub-kpc scale resolution, and spanning ~2 orders
of magnitude in gas mass (aided by gravitational lensing). Recently, it has
even become possible to directly identify distant galaxies through their
molecular emission lines without prior knowledge of their redshifts. The new
generation of powerful long wavelength interferometers such as the Expanded
Very Large Array (EVLA) and Atacama Large (sub)Millimeter Array (ALMA) thus
hold the promise to liberate studies of molecular gas in high redshift galaxies
from their heavy pre-selection. This will enable more systematic studies of the
molecular gas content in star-forming galaxies back to the earliest cosmic
times.

Cosmology and Nongalactic Astrophysics