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Detection of CH+, SH+, and their C-13- and S-34-isotopologues toward PKS 1830-211

Sebastien Muller (Institutionen för rymd-, geo- och miljövetenskap, Onsala rymdobservatorium) ; H. S. P. Muller ; John H. Black (Institutionen för rymd-, geo- och miljövetenskap, Astronomi och plasmafysik) ; M. Gerin ; F. Combes ; S. Curran ; E. Falgarone ; M. Guelin ; C. Henkel ; S. Martin ; K. M. Menten ; E. Roueff ; Susanne Aalto (Institutionen för rymd-, geo- och miljövetenskap, Astronomi och plasmafysik) ; A. Beelen ; T. Wiklind ; M. A. Zwaan
Astronomy and Astrophysics (0004-6361). Vol. 606 (2017),
[Artikel, refereegranskad vetenskaplig]

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 C-13- and S-34-isotopologues, as potential tracers of energetic processes in the interstellar medium. CH+ and (CH+)-C-13 are detected toward both images of PKS 1830-211, CH+ showing the deepest and broadest absorption among all species observed so far. The [CH+]/[(CH+)-C-13] abundance ratio is similar to 100 in the south-west line of sight. This value is larger than any previous [(CX)-C-12]/[(CX)-C-13] 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+]/[(CH+)-C-13], 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 C-13 isotopologue, SH+ and (SH+)-S-34 are only detected on the south-west sightline. These are the first detections of extragalactic SH+ and interstellar (SH+)-S-34. The spectroscopic parameters of SH+ are reevaluated and improved rest frequencies of (SH+)-S-34 are obtained. The [CH+]/[SH+] column density ratios show a large difference between the two lines of sight: similar to 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 greater than or similar to 10%, with SH+ tracing significantly higher molecular fractions than CH+.

Nyckelord: quasars: absorption lines, quasars: individual: PKS 1830-211, galaxies: ISM, galaxies: abundances, ISM: molecules, radio lines: galaxies

Denna post skapades 2017-11-16. Senast ändrad 2017-11-16.
CPL Pubid: 253179


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