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