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arXiv · 1707.07446

Detection of CH+, SH+, and their 13C- and 34S- isotopologues toward PKS1830-211

S. Muller·H. S. P. M"uller·J. H. Black·M. G'erin·F. Combes·S. Curran·E. Falgarone·M. Gu'elin·C. Henkel·S. Mart'in·K. M. Menten·E. Roueff·S. Aalto·A. Beelen·T. Wiklind·M. A. Zwaan
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Abstract

The z=0.89 molecular absorber toward PKS1830-211 provides us with the opportunity to probe the chemical and physical properties of the interstellar medium in the disk of a galaxy at a look-back time of half the present age of the Universe. Recent ALMA observations of hydrides have unveiled the multi-phase composition of this source's interstellar medium along two absorbing sightlines. Here, we report ALMA observations of CH+ and SH+, and of their 13C- and 34S- isotopologues, as potential tracers of energetic processes in the interstellar medium. CH+ and 13CH+ are detected toward both images of PKS1830-211, CH+ showing the deepest and broadest absorption among all species observed so far. The [CH+]/[13CH+] abundance ratio is ~100 in the south-west line of sight. [...] Toward the north-east image, we find an even larger value of [CH+]/[13CH+], 146 +/- 43, although with a large uncertainty. This sightline intercepts the absorber at a larger galactocentric radius than the southwestern one, where material might be less processed in stellar nucleosynthesis. In contrast to CH+ and its 13C isotopologue, SH+ and 34SH+ are only detected on the south-west sightline. These are the first detections of extragalactic SH+ and interstellar 34SH+. The spectroscopic parameters of SH+ are reevaluated and improved rest frequencies of 34SH+ are obtained. The [CH+]/[SH+] column density ratios show a large difference between the two lines of sight: ~25 and >600 toward the SW and NE image, respectively. We are not able to shed light on the formation process of CH+ and SH+ with these data, but the differences in the two sightlines toward PKS1830-211 suggest that their absorptions arise from gas with molecular fraction gtrsim 10%, with SH+ tracing significantly higher molecular fractions than CH+.

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S. Muller, H. S. P. M"uller, J. H. Black, M. G'erin, F. Combes, S. Curran, E. Falgarone, M. Gu'elin, C. Henkel, S. Mart'in, K. M. Menten, E. Roueff, S. Aalto, A. Beelen, T. Wiklind, M. A. Zwaan. 2017-07-24. Detection of CH+, SH+, and their 13C- and 34S- isotopologues toward PKS1830-211. https://doi.org/10.1051/0004-6361%2F201731405

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