Variations in H2O+/H2O ratios toward massive star-forming regions

TL;DR

This study uses Herschel observations to analyze the ratios of H2O+ to H2O in various environments of high-mass star-forming regions, revealing significant variation and the presence of H2O+ in different astrophysical contexts.

Contribution

It provides new observational data on H2O+ and H2O ratios across diverse environments in massive star-forming regions, highlighting environmental dependence.

Findings

H2O+ detected in 9 of 10 sources across environments

H2O+/H2O ratios range from 0.01 to a few

Highest H2O+ column densities found in outflows

Abstract

Early results from the Herschel Space Observatory revealed the water cation H2O+ to be an abundant ingredient of the interstellar medium. Here we present new observations of the H2O and H2O+ lines at 1113.3 and 1115.2 GHz using the Herschel Space Observatory toward a sample of high-mass star-forming regions to observationally study the relation between H2O and H2O+ . Nine out of ten sources show absorption from H2O+ in a range of environments: the molecular clumps surrounding the forming and newly formed massive stars, bright high-velocity outflows associated with the massive protostars, and unrelated low-density clouds along the line of sight. Column densities per velocity component of H2 O+ are found in the range of 10^12 to a few 10^13 cm-2 . The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H2O+/H2O are determined in a range from 0.01 to a few and are found to differ strongly between the observed environments with much lower ratios in the massive (proto)cluster envelopes (0.01-0.1) than in outflows and diffuse clouds. Remarkably, even for source components detected in H2O in emission, H2O+ is still seen in absorption.