ATCA detections of massive molecular gas reservoirs in dusty, high-z
  radio galaxies
  Observations using the 7 mm receiver system on the Australia Telescope
Compact Array have revealed large reservoirs of molecular gas in two
high-redshift radio galaxies: HATLAS J090426.9+015448 (z = 2.37) and HATLAS
J140930.4+003803 (z = 2.04). Optically the targets are very faint, and
spectroscopy classifies them as narrow-line radio galaxies. In addition to
harbouring an active galactic nucleus the targets share many characteristics of
sub-mm galaxies. Far-infrared data from Herschel-ATLAS suggest high levels of
dust (>10^9 M_solar) and a correspondingly large amount of obscured star
formation (~1000 M_solar / yr). The molecular gas is traced via the J = 1-0
transition of 12CO, its luminosity implying total H_2 masses of (1.7 +/- 0.3) x
10^11 and (9.5 +/- 2.4) x 10^10 (alpha_CO/0.8) M_solar in HATLAS
J090426.9+015448 and HATLAS J140930.4+003803 respectively. Both galaxies
exhibit molecular line emission over a broad (~1000 km/s) velocity range, and
feature double-peaked profiles. We interpret this as evidence of either a large
rotating disk or an on-going merger. Gas depletion timescales are ~100 Myr. The
1.4 GHz radio luminosities of our targets place them close to the break in the
luminosity function. As such they represent `typical' z > 2 radio sources,
responsible for the bulk of the energy emitted at radio wavelengths from
accretion-powered sources at high redshift, and yet they rank amongst the most
massive systems in terms of molecular gas and dust content. We also detect 115
GHz rest-frame continuum emission, indicating a very steep high-radio-frequency
spectrum, possibly classifying the targets as compact steep spectrum objects.
