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

Abstract

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 13 C-and 34 S-isotopologues, as potential tracers of energetic processes in the interstellar medium. CH + and 13 CH + are detected toward both images of PKS 1830−211, CH + showing the deepest and broadest absorption among all species observed so far. The [CH + ]/[ 13 CH + ] abundance ratio is ∼100 in the southwest line of sight. This value is larger than any previous [ 12 CX]/[ 13 CX] 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 northeast image, we find an even larger value of [CH + ]/[ 13 CH + ], 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 13 C isotopologue, SH + and 34 SH + are only detected on the southwest sightline. These are the first detections of extragalactic SH + and interstellar 34 SH +. The spectroscopic parameters of SH + are reevaluated and improved rest frequencies of 34 SH + 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 + .

Cool outflows in galaxies and their implications

“…The CH + molecule is a very useful tracer of turbulence in interstellar gas (e.g., Falgarone and Puget 1995;Myers et al 2015). Only few extragalactic studies of CH + have been carried out (e.g., Welty et al 2014;Muller et al 2017). One concerns the discovery of large turbulent reservoirs of molecular gas surrounding some highredshift galaxies through the detection of the CH + (J =1-0) transition, both in emission and absorption (Falgarone et al 2017).…”

The First Laboratory Detection of Vibration-rotation Transitions of 12CH+ and 13CH+ and Improved Measurement of Their Rotational Transition Frequencies

“…The observation of the CH + J = 1 − 0 rotational transition at ~ 835 GHz from ground, however, is hindered by a strong telluric oxygen line. One way out is the observation of the 13 CH + isotopologue at ~ 830 GHz, which has been detected with the CSO and APEX telescopes under very good weather conditions (Falgarone et al 2005; Menten et al 2011), or the observation of CH + in red-shifted extragalactic sources in the mm-wave region, as detected with ALMA towards the blazar PKS 1830-211 (Muller et al 2017) and a group of starburst galaxies (Falgarone et al 2017). Local observations of the rotational lines of CH + require satellite missions.…”

The Role of Terahertz and Far-IR Spectroscopy in Understanding the Formation and Evolution of Interstellar Prebiotic Molecules

“…Other instruments and telescopes have also aided greatly in the elucidation of the chemical complexity of the diffuse interstellar medium. For example, APEX, the Atacama Large Millimeter/ Submillimeter Array (ALMA), and the GREAT instrument aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) have all been used in the detection of sulfur-bearing molecules, including isotopologues (Menten et al, 2011;Neufeld et al, 2012bNeufeld et al, , 2015Muller et al, 2017). Perhaps the most exciting of all has been the series of recent ALMA observations of complex molecules.…”