2011ApJ...742L..21M

We report the first detection of hydrogen fluoride (HF) toward a high-redshift quasar. Using the Caltech Submillimeter Observatory, we detect the HF J = 1-0 transition in absorption toward the Cloverleaf, a broad absorption line quasi-stellar object at z = 2.56. The detection is statistically significant at the ∼6σ level. We estimate a lower limit of 4x10¹⁴/cm2 for the HF column density and using a previous estimate of the hydrogen column density, we obtain a lower limit of 1.7x10^–9 for the HF abundance. This value suggests that, assuming a Galactic N(HF)/N_Hratio, HF accounts for at least ∼10% of the fluorine in the gas phase along the line of sight to the Cloverleaf quasar. This observation corroborates the prediction that HF should be a good probe of the molecular gas at high redshift. Measurements of the HF abundance as a function of redshift are urgently needed to better constrain the fluorine nucleosynthesis mechanism(s).