Letter to the Editor

Detection of HNC and tentative detection of CN at z = 3.9

¹ IRAM, Domaine Universitaire, 300 rue de la piscine, St Martin d'Hères, 38400, France e-mail: guelin@iram.fr
² Observatorio Astronómico Nacional, Calle Alfonso XII 3, 28014 Madrid, Spain
³ IEM-DAMIR, CSIC, Serrano 121, 28006, Spain
⁴ Dept. of Physics and Astronomy, State Univ. of N.Y., Stony Brook, NY 11974, USA
⁵ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
⁶ NRAO, 520 Edgemont road, Charlottesville, VA 22903, USA

Received: 12 October 2006
Accepted: 7 December 2006

Abstract

Aims.Molecular line emission from high-redshift galaxies holds great promise for the study of galaxy formation and evolution.

Methods.The weak signals can only be detected with the largest mm-wave telescopes, such as the IRAM interferometer.

Results.We report the detection of the line of HNC and the tentative detection of the line of CN in the quasar APM 08279+5255 at . These are the 4th and 5th molecular species detected at such a high redshift. The derived HNC and CN line intensities are 0.6 and 0.4 times that of HCN . If HNC and HCN are co-spatial and if their lines are collisionally excited, the [HNC]/[HCN] abundance ratio must be equal to 0.6 within a factor of 2, similar to its value in the cold Galactic clouds and much larger than in the hot molecular gas associated with Galactic HII regions. It is possible, however, that fluorescent infrared radiation plays an important role in the excitation of HNC and HCN.