Herschel-HIFI observations of H2O in high-mass star-forming regions: first results

TL;DR

This study presents initial Herschel-HIFI observations of water in high-mass star-forming regions, identifying different gas-phase water components and their varying abundances influenced by environmental conditions.

Contribution

It provides the first observational results of water emission in high-mass star-forming regions using Herschel-HIFI, categorizing water into cloud, envelope, and outflow components.

Findings

Low water abundance in clouds and envelopes due to photodissociation and freeze-out.

Higher water abundance in outflows from grain mantle evaporation and reactions.

Identification of three distinct water components in star-forming regions.

Abstract

This paper reviews the first results of observations of H2O line emission with Herschel-HIFI towards high-mass star-forming regions, obtained within the WISH guaranteed time program. The data reveal three kinds of gas-phase H2O: `cloud water' in cold tenuous foreground clouds, `envelope water' in dense protostellar envelopes, and `outflow water' in protostellar outflows. The low H2O abundance (1e-10 -- 1e-9) in foreground clouds and protostellar envelopes is due to rapid photodissociation and freeze-out on dust grains, respectively. The outflows show higher H2O abundances (1e-7 -- 1e-6) due to grain mantle evaporation and (probably) neutral-neutral reactions.