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 MRC0152-209 (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 widespread, low-density, and sub-thermally 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 × 1010 K km s-1 pc2 for MRC0152-209, which is comparable to that derived from CO(1-0) observations of several high-z submillimeter and star-forming BzK galaxies. The CO(1-0) traces a total molecular hydrogen mass of = 5 × 1010 (αx/0.8) M. MRC0152-209 is an infrared 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 α = -1.3 between 1.4 and 40 GHz (4-115 GHz in the galaxy's rest frame). MRC0152-209 is part of an ongoing systematic ATCA/CABB survey of CO(1-0) in high-z radio galaxies between 1.7 < z < 3.