  Recent observations reveal galaxies in the early Universe (2<z<6.4) with
large reservoirs of molecular gas and extreme star formation rates. For a very
large range of sources, a tight relationship exists between star formation rate
and the luminosity of the HCN J=1-0 spectral line, but sources at redshifts of
z~2 and beyond do not follow this trend. The deficit in HCN is conventionally
explained by an excess of infrared (IR) radiation due to active galactic nuclei
(AGN). We show in this letter not only that the presence of AGN cannot account
for the excess of IR over molecular luminosity, but also that the observed
abundance of HCN is in fact consistent with a population of stars forming from
near-primordial gas.
