CO LINES FROM GIANT ARCS IN CLUSTERS

We present observations of the CO emission from 4 giant arcs in cluste rs of galaxies, made with the IRAM 30m telescope. These arcs are the i mages of distant galaxies magnified by the gravitational lensing effec t of the foreground cluster. The redshifts of the observed objects ran ge from 0.7 to 2.2. We have detected the CO(2-1) line associated with the bright are in the cluster Abell 370, at a redshift of 0.725. With reasonable assumptions the molecular mass in this object can be estima ted to be 1.410(9) M., similar to that found in our own galaxy. For th e three other arcs we get upper limits which range between 410(9) M. a nd 710(9) M.. Among the few objects at cosmological distances which ha ve confirmed detections of CO lines in emission, gravitational lensing is at play in at least two: the Cloverleaf and IRAS10214+4724. In bot h sources the amplification factor is still very uncertain. Our detect ion of CO emission in A370 shows that with the the help of ''gravitati onal telescopes'' one can study the gaseous content of normal galaxies at look back times of one third of the age of the Universe.