  Molecular line emission from high-redshift galaxies holds great promise for
the study of galaxy formation and evolution. The weak signals can only be
detected with the largest mm-wave telescopes, such as the IRAM interferometer.
We report the detection of the J = 5-4 line of HNC and the tentative detection
of the N= 4-3 line of CN in the quasar APM08279+5255 at z=3.9. 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 J= 5-4. If HNC and
HCN are co-spatial and if their J= 5-4 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.

Astrophysics