1996A&A...309..416I

Previous searches for far-infrared line emission from high-redshift objects have concentrated on C⁺ at 158-µm which, for the furthest known (z>4) systems, falls in the atmospheric window between 300 and 380GHz. Here, we describe a search for the ³P₁->³P₀ ground state fine-structure N⁺ line at 205-µm, which is shifted into the same window for 2.85<z<3.87. This redshift range contains several well-known systems, including 4C41.17, a radiogalaxy undergoing rapid star formation, and PC2047+0123, a radio-quiet quasar which appears to contain a large quantity of dust. This N⁺ search was intended to complement our search for CO(J=1->0) from 4C41.17 using the Very Large Array (Ivison et al. 1996), and to test the ability of the James Clerk Maxwell Telescope to detect faint lines. Our data cover 2000km/s for 4C41.17, centred at the expected position of N⁺ for z=3.800; for PC2047+0123 the velocity coverage is 1380kms^–1, centred at the line position for z=3.799. We set a 3-σ upper limit of 1.6K.km/s on the N⁺ integrated line intensity for 4C41.17, and 1.8K.km/s for PC2047+0123, for an assumed line width of 400km/s. These values correspond to N⁺ line-luminosity limits several orders of magnitude above those of M82 and the Milky Way, and astronomically useful progress would therefore seem to be dependent on the commissioning of large submillimetre arrays and further advances in receiver technology.