MOLECULAR GAS CONTENT OF THE PRIMEVAL GALAXY IRAS-10214+4724

THE faint IRAS source 10214 + 4724, identified 1 with a distant galaxy at redshift z = 2.286, is one of the most intrinsically luminous objects in the Universe, with L almost-equal-to 10(14) L. (where L. is the solar luminosity). The remarkable detection of emission from neutral CO (ref. 2) leads, by comparison with similar detections in nearby galaxies, to an estimate of 2-6 x 10(11) M. for the mass of neutral molecular hydrogen in this galaxy. This is 30-90 times less than the estimate given in ref. 2, but still comparable to the total mass (gas, dust and stars) of a large spiral galaxy. This gas mass is consistent with the dynamical mass of the galaxy inferred from the CO emission line-width. The CO line luminosity is twenty times larger than is seen in nearby (z < 0.3) ultra-luminous (L > 3 x 10(11) M.) galaxies 3-5. Although it is extremely gas-rich, with a higher CO luminosity than any other galaxy, the infrared to CO luminosity ratio of 10214 + 4724 is twice that of most infrared-luminous galaxies, and approximately 30 times higher than that of normal spirals. Its infrared colours and high infrared/CO luminosity ratio indicate that 10214 + 4724 is similar to nearby ultra-luminous galaxies 5 that are known to be merging. This galaxy is a primaeval molecular galaxy with the mass of a large spiral, but with most of the mass in molecular gas rather than stars.