Water at z=2.286?

We have used the IRAM 30m telescope to search for rotational lines of water and molecular oxygen in the very distant galaxy IRAS 10214+4724 at a redshift of 2.286. We report the tentative detection of the 2 11 → 2 02 para transition of H 2 O at 752.0 GHz. This would be the first time that a thermal rotational line of water is detected. The ortho transitions 1 10 → 1 01 and 4 14 → 3 21 at 556.9 and 380.2 GHz are not detected with intensities at most twice that of the detected 752 GHz line. We cannot derive the water abundance since the line is likely optically thick. Assuming that the levels are thermalised at 100 K, the surface filling factor of the H 2 O emitting cores with respect to the total galaxy size of 8 kpc is about 3 10 −3