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Astron. Astrophys. 354, L1-L5 (2000)

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Letter to the Editor

CO detection of the extremely red galaxy HR10

Paola Andreani 1, Andrea Cimatti 2, Laurent Loinard 3 and Huub Röttgering 4

1 Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy (andreani@pd.astro.it)
Present-address: Max-Planck-Institut fü Extraterrestrische Physik, Postfach 1603, 85740 Garching, Germany
2 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy (cimatti@arcetri.astro.it)
3 Institut de Radioastronomie Millimétrique, 300, rue de la Piscine, St. Martin d'Hères, France (loinard@iram.fr)
4 Sterrewacht Leiden, Sterrewacht, Postbus 9513, Leiden 2300 RA, The Netherlands (rottgeri@strw.leidenuniv.nl)

Received 2 July 1999 / Accepted 14 January 2000


CO [FORMULA] and [FORMULA] emission lines were detected towards the extremely red galaxy (ERG) HR10 (J164502+4626.4) at [FORMULA]. The CO intensities imply a molecular gas mass M(H2) of [FORMULA] h[FORMULA] [FORMULA], 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 430 km s-1 from the H[FORMULA] line. These CO detections confirm the previous results that HR10 is a highly obscured object with a large thermal far-infrared luminosity and a high star-formation rate. The overall properties of HR10 (CO detection, [FORMULA] to L[FORMULA] 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.

Key words: galaxies: formation – galaxies: ISM – galaxies: starburst

Send offprint requests to: P. Andreani

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© European Southern Observatory (ESO) 2000

Online publication: January 31, 2000