English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We combine Herschel observations of a total of 12 sources to construct themost uniform survey of HF and H2O in our Galactic disk. Both molecules aredetected in absorption along all sight lines. The high spectral resolution ofthe Heterodyne Instrument for the Far-Infrared (HIFI) allows us to compare theHF and H2O distributions in 47 diffuse cloud components sampling the disk. Wefind that the HF and H2O velocity distributions follow each other almostperfectly and establish that HF and H2O probe the same gas-phase volume. Ourobservations corroborate theoretical predictions that HF is a sensitive tracerof H2 in diffuse clouds, down to molecular fractions of only a few percent.Using HF to trace H2 in our sample, we find that the N(H2O)-to-N(HF) ratioshows a narrow distribution with a median value of 1.51. Our results furthersuggest that H2O might be used as a tracer of H2 -within a factor 2.5- in thediffuse interstellar medium. We show that the measured factor of ~2.5 variationaround the median is driven by true local variations in the H2O abundancerelative to H2 throughout the disk. The latter variability allows us to testour theoretical understanding of the chemistry of oxygen-bearing molecules inthe diffuse gas. We show that both gas-phase and grain-surface chemistry arerequired to reproduce our H2O observations. This survey thus confirms thatgrain surface reactions can play a significant role in the chemistry occurringin the diffuse interstellar medium n_H < 1000 cm^-3.

A Herschel/HIFI Legacy Survey of HF and H2O in the Galaxy: Probing Diffuse Molecular Cloud Chemistry