Detection of CH+, SH+, and their C-13- and S-34-isotopologues toward PKS 1830-211
Artikel i vetenskaplig tidskrift, 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 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+.

radio lines: galaxies

galaxies: ISM

quasars: absorption lines

ISM: molecules

quasars: individual: PKS 1830-211

galaxies: abundances


Sebastien Muller

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

Holger Muller

Universität zu Köln

John H Black

Astronomi och plasmafysik

M. Gerin

Ecole Normale Superieure (ENS)

F. Combes

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

S. Curran

Victoria University of Wellington

E. Falgarone

Ecole Normale Superieure (ENS)

M. Guelin

Institut de RadioAstronomie Millimetrique (IRAM)

Ecole Normale Superieure (ENS)

C. Henkel

King Abdulaziz University

Max Planck-institutet

S. Martin

European Southern Observatory Santiago

Atacama Large Millimeter-submillimeter Array (ALMA)

K. M. Menten

Max Planck-institutet

E. Roueff

Ecole Normale Superieure (ENS)

Susanne Aalto

Astronomi och plasmafysik

A. Beelen

Université Paris-Sud

Tommy Wiklind

Catholic University of America

M. A. Zwaan

European Southern Observatory (ESO)

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 606 A109


Astronomi, astrofysik och kosmologi