Volume 606, October 2017
|Number of page(s)||10|
|Published online||20 October 2017|
Detection of CH+, SH+, and their 13C- and 34S-isotopologues toward PKS 1830−211
1 Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
2 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
3 LERMA/LRA, École Normale Supérieure, Observatoire de Paris, CNRS UMR 8112, PSL Research University, Sorbonne Universités, UPMC Université Paris, 24 rue Lhomond, 75005 Paris, France
4 Observatoire de Paris, LERMA, Collège de France, CNRS, PSL Univ., UPMC, Sorbonne Univ., 75014 Paris, France
5 School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, 6140 Wellington, New Zealand
6 Institut de Radioastronomie Millimétrique, 300 rue de la piscine, 38406 St Martin d’ Hères, France
7 Max-Planck-Institut für Radioastonomie, Auf dem Hügel 69, 53121 Bonn, Germany
8 Astron. Dept., King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
9 European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago, Chile
10 Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, 7630355 Santiago, Chile
11 Institut d’Astrophysique Spatiale, Bât. 121, Université Paris-Sud, 91405 Orsay Cedex, France
12 Department of Physics, Catholic University of America, 620 Michigan Ave NE, Washington DC 20064, USA
13 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
Received: 19 June 2017
Accepted: 21 July 2017
The z = 0.89 molecular absorber toward PKS 1830−211 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 PKS 1830−211, 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. This value is larger than any previous [12CX]/[13CX] ratios determined from other species toward this source and suggests either that the latter might be affected by fractionation or that CH+ might be tracing a different gas component. 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 between the two sightlines toward PKS 1830−211 suggest that their absorptions arise from gas with a molecular fraction of ≳10%, with SH+ tracing significantly higher molecular fractions than CH+.
Key words: quasars: absorption lines / quasars: individual: PKS 1830 / 211 / galaxies: ISM / galaxies: abundances / ISM: molecules / radio lines: galaxies
© ESO, 2017
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