1996A&A...306L..41C

We present observations of the CO emission from 4 giant arcs in clusters of galaxies, made with the IRAM 30m telescope. These arcs are the images of distant galaxies magnified by the gravitational lensing effect of the foreground cluster. The redshifts of the observed objects range from 0.7 to 2.2. We have detected the CO(2-1) line associated with the bright arc in the cluster Abell 370, at a redshift of 0.725. With reasonable assumptions the molecular mass in this object can be estimated to be 1.4x10⁹M_☉, similar to that found in our own galaxy. For the three other arcs we get upper limits which range between 4x10⁹M_☉ and 7x10⁹M_☉. Among the few objects at cosmological distances which have confirmed detections of CO lines in emission, gravitational lensing is at play in at least two: the Cloverleaf and IRAS10214+4724. In both sources the amplification factor is still very uncertain. Our detection of CO emission in A370 shows that with the the help of "gravitational telescopes" one can study the gaseous content of normal galaxies at look back times of one third of the age of the Universe.