CO(1-0) detection of molecular gas in the massive Spiderweb Galaxy (z=2)
  The high-redshift radio galaxy MRC 1138-262 (`Spiderweb Galaxy'; z = 2.16),
is one of the most massive systems in the early Universe and surrounded by a
dense `web' of proto-cluster galaxies. Using the Australia Telescope Compact
Array, we detected CO(1-0) emission from cold molecular gas -- the raw
ingredient for star formation -- across the Spiderweb Galaxy. We infer a
molecular gas mass of M(H2) = 6x10^10 M(sun) (for M(H2)/L'(CO)=0.8). While the
bulk of the molecular gas coincides with the central radio galaxy, there are
indications that a substantial fraction of this gas is associated with
satellite galaxies or spread across the inter-galactic medium on scales of tens
of kpc. In addition, we tentatively detect CO(1-0) in the star-forming
proto-cluster galaxy HAE 229, 250 kpc to the west. Our observations are
consistent with the fact that the Spiderweb Galaxy is building up its stellar
mass through a massive burst of widespread star formation. At maximum star
formation efficiency, the molecular gas will be able to sustain the current
star formation rate (SFR ~ 1400 M(sun)/yr, as traced by Seymour et al.) for
about 40 Myr. This is similar to the estimated typical lifetime of a major
starburst event in infra-red luminous merger systems.
