Discovery of Hydrogen Fluoride in the Cloverleaf Quasar at z = 2.56

TL;DR

This paper reports the first detection of hydrogen fluoride in a high redshift quasar, demonstrating HF as a promising probe of molecular gas in the early universe and providing insights into fluorine nucleosynthesis.

Contribution

It presents the first observation of HF in a high redshift quasar, establishing HF as a useful tool for studying molecular gas at early cosmic times.

Findings

HF detected at ~6 sigma significance in the Cloverleaf quasar

HF accounts for at least 10% of fluorine in the gas phase

Lower limit of HF abundance estimated at 1.7 x 10^-9

Abstract

We report the first detection of hydrogen fluoride (HF) toward a high redshift quasar. Using the Caltech Submillimeter Observatory (CSO) we detect the HF J = 1 - 0 transition in absorption toward the Cloverleaf, a broad absorption line (BAL) quasi-stellar object (QSO) at z=2.56. The detection is statistically significant at the ~ 6 sigma level. We estimate a lower limit of 4 \times 1014 cm-2 for the HF column density and using a previous estimate of the hydrogen column density, we obtain a lower limit of 1.7 \times 10-9 for the HF abundance. This value suggests that, assuming a Galactic N(HF)/NH ratio, 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).