Observation of H2O in a strongly lensed Herschel-ATLAS source at z=2.3
  The Herschel survey, H-ATLAS, with its large areal coverage, has recently
discovered a number of bright, strongly lensed high-z submillimeter galaxies.
The strong magnification makes it possible to study molecular species other
than CO, which are otherwise difficult to observe in high-z galaxies. Among the
lensed galaxies already identified by H-ATLAS, the source J090302.9-014127B
(SDP.17b) at z = 2.305 is remarkable due to its excitation conditions and a
tentative detection of the H2O 202-111 emission line (Lupu et al. 2010). We
report observations of this line in SDP.17b using the IRAM interferometer
equipped with its new 277- 371GHz receivers. The H2O line is detected at a
redshift of z = 2.3049+/-0.0006, with a flux of 7.8+/-0.5 Jy km s-1 and a FWHM
of 250+/-60 km s-1. The new flux is 2.4 times weaker than the previous
tentative detection, although both remain marginally consistent within
1.6-sigma. The intrinsic line luminosity and ratio of H2O(202-111)/CO8-7 seem
comparable with those of the nearby starburst/enshrouded-AGN Mrk 231,
suggesting that SDP.17b could also host a luminous AGN. The detection of a
strong H2O 202-111 line in SDP.17b implies an efficient excitation mechanism of
the water levels that must occur in very dense and warm interstellar gas.
