Herschel/HIFI Observations of Hydrogen Fluoride Toward Sagittarius B2(M)

TL;DR

This study uses Herschel/HIFI to observe hydrogen fluoride absorption toward Sagittarius B2(M), revealing its distribution, abundance, and unique spectral features, and comparing it with other molecules like water and CO.

Contribution

First detailed HF absorption analysis toward Sagittarius B2(M), showing its widespread presence and unique spectral features compared to other molecules.

Findings

HF abundance relative to H2 is ~1.3×10^-8

HF shows unique absorption features not seen in other molecules

Water is more abundant than HF across many velocities

Abstract

Herschel/HIFI observations have revealed the presence of widespread absorption by hydrogen fluoride (HF) J = 1-0 rotational transition, toward a number of Galactic sources. We present observations of HF J = 1-0 toward the high-mass star-forming region Sagittarius B2(M). The spectrum obtained shows a complex pattern of absorption, with numerous features covering a wide range of local standard of rest velocities (-130 to 100 km -1). An analysis of this absorption yields HF abundances relative to H2 of ~1.3 {\times}10-8, in most velocity intervals. This result is in good agreement with estimates from chemical models, which predict that HF should be the main reservoir of gas-phase fluorine under a wide variety of interstellar conditions. Interestingly, we also find velocity intervals in which the HF spectrum shows strong absorption features that are not present, or are very weak, in spectra of other molecules, such as 13CO (1-0) and CS (2-1). HF absorption reveals components of diffuse clouds with small extinction that can be studied for the first time. Another interesting observation is that water is significantly more abundant than hydrogen fluoride over a wide range of velocities toward Sagittarius B2(M), in contrast to the remarkably constant H2O/HF abundance ratio with average value close to unity measured toward other Galactic sources.