2000A&A...354L...1A

CO J=5-4 and J=2-1 emission lines were detected towards the extremely red galaxy (ERG) HR 10 (J164502+4626.4) at z=1.44. The CO intensities imply a molecular gas mass M(H₂) of 1.6x10¹¹h^–2₅₀M_☉, and, combined with the intensity of the dust continuum, a gas-to-dust mass ratio around 200-400 (assuming galactic values for the conversion factors). The peak of the CO lines are at the same redshift as the [OII]3727 line, but blue-shifted by 430km/s from the Hα line. These CO detections confirm the previous results that HR 10 is a highly obscured object with a large thermal far-infrared luminosity and a high star-formation rate. The overall properties of HR 10 (CO detection, L_FIR to L'_CO ratio, and FIR to radio flux ratio) clearly favour the hypothesis that its extreme characteristics are related to star-formation processes rather than to a hidden AGN.