Journal: Transactions of IAA RAS vol. 41
Keywords: Galaxies, high-redshift, radio-lines.
Molecular lines have been widely used for the study of galaxy formation and evolution at high-redshift. Of special interest is how the relation between the star formation rate and the dense-gas content varies with redshift. Fair tracers of the dense gas are key to understanding the first phases of galaxy formation. We present for the first time, the detection of the two rotational transitions CN(5–4)@115 GHz and CN(6–5)@138 GHz, in the z ∼ 4 quasar APM 08279 with the IRAM Plateau de Bure interferometer (PdBI). Together with current information on the CN(4–3) line, we have modelled the Spectral Line Energy Distribution (SLED) of CN and derived its molecular abundance in APM 08279. Based on the previous model of the CO molecular emission from APM 08279 we have performed a preliminary analysis of the CN molecular excitation using the radiative transfer code RADEX. To reproduce the observed CN line intensities and the overall SLED, molecular abundances of 5 · 10¯⁸ − 5 · 10¯⁶ are needed. We conclude that the CN emission in APM 08279 is mostly free from IR pumping, and therefore is a fair tracer of the dense-molecular gas at high redshift.