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Astron. Astrophys. 321, 389-396 (1997)

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A search for molecular gas in high redshift radio galaxies

R. van Ojik 1, H.J.A. Röttgering 1, 2, 3, P.P. van der Werf 1, G.K. Miley 1, C.L. Carilli 1, 4, A. Visser 1, K.G. Isaak 2, M. Lacy 5, T. Jenness 2, J. Sleath 2 and J. Wink 6

1 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands
2 Mullard Radio Astronomy Observatory, Cavendish Laboratory, Cambridge CB3 0HE, UK
3 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
4 NRAO, P.O. Box 0, Socorro, NM 87801, USA
5 Astrophysics, Department of Physics, Keble Road, Oxford, OX1 3RH, UK
6 Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, F-38406 St. Martin d'Hères Cedex, France

Received 18 December 1995 / Accepted 27 September 1996


We present results of an extensive search for molecular gas in 14 high redshift ([FORMULA]) radio galaxies. Radio galaxies with redshifts between 2.0 and 4.3 were observed during several sessions on two different single-dish telescopes (IRAM and JCMT) and two interferometric arrays (VLA and OVRO). No significant CO emission to a 2 [FORMULA] limit of a few times [FORMULA] K km s-1 pc2 was detected in any of these objects. The limits on the CO emission achieved indicate that, assuming a CO-H2 conversion factor similar to the Galactic value, the mass of enriched molecular gas in these galaxies is less than [FORMULA] M [FORMULA]. This suggests that distant radio galaxies may not be forming stars at the extremely high rates that have earlier been proposed, although they may still be forming stars at rates comparable to those of local starburst galaxies.

Key words: galaxies: active – galaxies: ISM – radio lines: galaxies – radio continuum: galaxies

Send offprint requests to: H.J.A. Röttgering (Leiden address)

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998