Dust opacities in dense regions

We report the detection of OH+ and H2O+ in the z=0.89 absorber toward the lensed quasar PKS1830-211. The abundance ratio of OH+ and H2O+ is used to quantify the molecular hydrogen fraction (fH2) and the cosmic-ray ionization rate of atomic hydrogen (zH) along two lines of sight, located at ~2 kpc and ~4 kpc to either side of the absorber's center. The molecular fraction decreases outwards, from ~0.04 to ~0.02, comparable to values measured in the Milky Way at similar galactocentric radii. For zH, we find values of ~2x10^-14 s^-1 and ~3x10^-15 s^-1, respectively, which are slightly higher than in the Milky Way at comparable galactocentric radii, possibly due to a higher average star formation activity in the z=0.89 absorber. The ALMA observations of OH+, H2O+, and other hydrides toward PKS1830-211 reveal the multi-phase composition of the absorbing gas. Taking the column density ratios along the southwest and northeast lines of sight as a proxy of molecular fraction, we classify the species ArH+, OH+, H2Cl+, H2O+, CH, and HF as tracing gases increasingly more molecular. Incidentally, our data allow us to improve the accuracy of H2O+ rest frequencies and thus refine the spectroscopic parameters.

/pdf/oh-and-h2o-absorption-toward-pks1830-211-1o1bcexs4v.pdf

OH+ and H2O+ absorption toward PKS1830-211

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+.

/pdf/detection-of-ch-sh-and-their-13-c-and-34-s-isotopologues-4h93ntjgbx.pdf

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

We report the first extragalactic detection of the fluoromethylidynium ion CF+ in the z = 0.89 absorber toward PKS 1830-211. We estimate an abundance of similar to 3 x 10(-10) relative to H-2 and that similar to 1% of fluorine is captured in CF+. The absorption line profile of CF+ is found to be markedly different from that of other species observed within the same tuning, and is notably anticorrelated with CH3OH. On the other hand, the CF+ profile resembles that of [CI]. Our results are consistent with expected fluorine chemistry and point to chemical differentiation in the column of absorbing gas.

/pdf/detection-of-extragalactic-cf-toward-pks-1830-211-chemical-3ouxr80slf.pdf

Detection of extragalactic CF+ toward PKS 1830−211 - Chemical differentiation in the absorbing gas

We report the first extragalactic detection of CF+, the fluoromethylidynium ion, in the z=0.89 absorber toward PKS1830-211. We estimate an abundance of ~3E-10 relative to H2 and that ~1% of fluorine is captured in CF+. The absorption line profile of CF+ is found to be markedly different from that of other species observed within the same tuning, and is notably anti-correlated with CH3OH. On the other hand, the CF+ profile resembles that of [C I]. Our results are consistent with expected fluorine chemistry and point to chemical differentiation in the column of absorbing gas.

/pdf/detection-of-extragalactic-cf-toward-pks1830-211-chemical-1cnl7qzmni.pdf

Detection of extragalactic CF+ toward PKS1830-211 -- Chemical differentiation in the absorbing gas

Based on measurements with the Effelsberg 100-m telescope, a multiline study of molecular species is presented toward the southwestern source of the gravitational lens system PKS 1830–211, which is by far the best known target for studying molecular gas in absorption at intermediate redshift. Determining line parameters and optical depths and performing large velocity gradient radiative transfer calculations, the aims of this study are (1) to evaluate physical parameters of the absorbing foreground gas at z ~ 0.89, in particular its homogeneity; and (2) to monitor the spectroscopic time variability caused by fluctuations in the z ~ 2.5 background continuum source. We find, that the gas is quite inhomogeneous with n(H2) ~ 2 × 103 cm-3 for most molecular species but with higher values for H2CO and lower ones for SO. Measuring the CS J = 1 ← 0 transition during a time interval of more than a decade, from 2001 to 2012, the peak absorption depth of the line remains approximately constant, while the line shape undergoes notable variations. Covering the time between 1996 and 2013, CS, HCO+, and CH3OH data indicate maximum integrated optical depths in ~2001 and 2011/2012. This is compatible with a ~10 yr periodicity, which, however, needs confirmation by substantially longer time monitoring. Comparing molecular abundances with those of different types of Galactic and nearby extragalactic clouds we find that the observed cloud complex does not correspond to one particular type but to a variety of cloud types with more diffuse and denser components as can be expected for an observed region with a transverse linear scale of several parsec and a likely greater depth along the line of sight. A tentative detection of Galactic absorption in the c-C3H2 110−101 line at 18.343 GHz is also reported.

/pdf/the-inhomogeneous-ism-toward-pks-1830-211-sw-a-detailed-view-1kclw76ug4.pdf

The inhomogeneous ISM toward PKS 1830–211 SW: A detailed view of molecular gas at a look-back time of 7.5 Gyr

We performed a multi-line NH 3 and CS excitation study with the highest possible single-dish resolution to analyze the temperature and density structure of the NGC 2024 molecular cloud core. A physically consistent picture is presented that matches both the presently available molecular line and dust continuum data

Dense clumps in NGC 2024 ― protostellar condensations ?

It has been suggested that in NGC 2024 star forming processes are still going on, and dense cores found by 1.3 mm continuum observations are identified as possible protostellar condensations. To trace the molecular gas of high density, we observed the CS (J=7-6) line using the 30 m IRAM MRT for the first time at submillimetre frequencies (spat, resol. 8.5”). These and complementary observations of lower J CS/C 34 S transitions as well as the temperature probing NH3(1,1) and (2,2) non-metastable lines enable us to determine temperature and density of 3 selected cores, their kinematics and their masses. These parameters are compared with what is expected for protostellar condensations.

/pdf/dense-clumps-in-ngc-2024-protostellar-condensations-4164nwwx95.pdf

Dense clumps in NGC 2024 — Protostellar condensations?

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The inhomogeneous ISM toward PKS 1830–211 SW: A detailed view of molecular gas at a look-back time of 7.5 Gyr

Dense clumps in NGC 2024 ― protostellar condensations ?

Dense clumps in NGC 2024 — Protostellar condensations?