Variations in H2O+/H2O ratios toward massive star-forming regions
de Graauw, Th.; Falgarone, E.; Liseau, R.; Braine, J.; Codella, C.; Dominik, C.; Ossenkopf, V.; Bontemps, S.; Benedettini, M.; van Dishoeck, E. F.; Bachiller, R.; Larsson, B.; Cernicharo, J.; Daniel, F.; Encrenaz, P.; Gerin, M.; Goicoechea, J. R.; Johnstone, D.; Pearson, J. C.; Plume, R.; Stutzki, J.; Olberg, M.; Melnick, G.; Risacher, C.; Fuente, A.; Benz, A. O.; Bruderer, S.; van der Tak, F.; Wyrowski, F.; Black, J. H.; Shipman, R.; Beintema, D.; Dieleman, P.; Fich, M.; Herpin, F.; de Jonge, A.; McCoey, C.; Whyborn, N.; Bjerkeli, P.; Marseille, M.; Nisini, B.; Caselli, P.; Lis, D.; Kristensen, L. E.; Hogerheijde, M. R.; Tafalla, M.; Giannini, T.; Saraceno, P.; Herczeg, G. J.; Doty, S. D.; Baudry, A.; Bergin, E.; di Giorgio, A. M.; Helmich, F.; Jacq, T.; Jørgensen, J. K.; Parise, B.; van Kempen, T. A.; Visser, R.; Yıldız, U. A.; Frieswijk, W.; Roelfsema, P.; Chavarria, L.; Blake, G.; Santiago, J.; Wampfler, S.
Germany, Netherlands, France, Switzerland, United Kingdom, Canada, Sweden, Spain, Italy, United States, Chile, Denmark
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 H2O+ are found in the range of 1012 to a few 1013 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.
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.