Molecular CO(1-0) gas in the z~2 radio galaxy MRC 0152-209

We report the detection of molecular CO(1-0) gas in the high-z radio galaxy MRC 0152-209 (z = 1.92) with the Australia Telescope Compact Array Broadband Backend (ATCA/CABB). This is the third known detection of CO(1-0) in a high-z radio galaxy to date. CO(1-0) is the most robust tracer of the overall molecular gas content (including the wide-spread, low-density and subthermally excited component), hence observations of CO(1-0) are crucial for studying galaxy evolution in the Early Universe. We derive L'(CO) = (6.6 +- 2.0) x 10^10 K km/s pc^2 for MRC 0152-209, which is comparable to that derived from CO(1-0) observations of several high-z submillimetre and starforming BzK galaxies. The CO(1-0) traces a total molecular hydrogen mass of M(H2) = 5 x 10^10 (alpha_x/0.8) Msun. MRC 0152-209 is an infra-red bright radio galaxy, in which a large reservoir of cold molecular gas has not (yet) been depleted by star formation or radio source feedback. Its compact radio source is reliably detected at 40 GHz and has a steep spectral index of alpha = -1.3 between 1.4 and 40 GHz (4-115 GHz in the galaxy's rest-frame). MRC 0152-209 is part of an ongoing systematic ATCA/CABB survey of CO(1-0) in high-z radio galaxies between 1.7 < z < 3.
Comment: Accepted for publication in ApJL -- 8 pages, 3 figures