A SEARCH FOR N+ AT Z

Previous searches for far-infrared line emission from high-redshift ob jects have concentrated on C+ at 158-mu m which, for the furthest know n (z > 4) systems, falls in the atmospheric window between 300 and 380 GHz. Here, we describe a search for the P-3(1) --> P-3(0) ground stat e fine-structure N+ line at 205-mu m, which is shifted into the same w indow for 2.85 < z < 3.87. This redshift range contains several well-k nown systems, including 4C41.17, a radiogalaxy undergoing rapid star f ormation, and PC 2047+0123, a radio-quiet quasar which appears to cont ain a large quantity of dust. This N+ search was intended to complemen t our search for CO(J = I --> 0) from 4C41.17 using the Very Large Arr ay (Ivison et al. 1996), and to test the ability of the James Clerk Ma xwell Telescope to detect faint lines. Our data cover 2000 km s(-1) fo r 4C 41.17, centred at the expected position of N+ for z = 3.800; for PC 2047+0123 the velocity coverage is 1380 km s(-1), centred at the li ne position for z = 3.799. We set a 3-sigma upper limit of 1.6 K km s( -1) on the N+ integrated line intensity for 4C 41.17, and 1.8 K km s(- 1) for PC 2047+0123, for an assumed line width of 400 km s(-1) These v alues correspond to N+ line-luminosity limits several orders of magnit ude above those of M82 and the Milky Way, and astronomically useful pr ogress would therefore seem to be dependent on the commissioning of la rge submillimetre arrays and further advances in receiver technology.