ArH+ and p-H2O+ spectra towards 7 molecular clouds
Short Name:
J/A+A/643/A91
Date:
21 Oct 2021
Publisher:
CDS
Description:
One of the surprises of the Herschel mission was the detection of ArH+, toward the Crab Nebula in emission and in absorption toward strong Galactic background sources. Although, these detections were limited to the first quadrant of the Galaxy, the existing data suggests that ArH+ ubiquitously and exclusively probes the diffuse atomic regions of the interstellar medium. In this study we extend the coverage of ArH+ to other parts of the Galaxy with new observations of its J=1-0 transition along seven Galactic sight lines toward bright sub-millimetre continuum sources. We aim to benchmark its efficiency as a tracer of purely atomic gas by evaluating its correlation (or lack of correlation as suggested by chemical models) with other well known atomic gas tracers like OH+ and H_2_O+ and the molecular gas tracer CH. The observations of the J=1-0 line of ArH+ near 617.5GHz were made feasible with the new, sensitive SEPIA660 receiver on the APEX 12m telescope. Further, the two sidebands of this receiver allowed us to observe the N_KaKc_=1_1,0_-1_0,1_ transitions of para-H_2_O+ at 607.227GHz simultaneously with the ArH+ line. We model the optically thin absorption spectra of the different species and subsequently derived their column densities. By analysing the steady state chemistry of OH+ and o-H_2_O+ we derive on average a cosmic-ray ionisation rate of 2.3+/-0.3x10^-16^s^-1^, toward the sightlines studied in this work. Using the derived values of the cosmic-ray ionisation rates and the observed ArH+ abundances we constrain the molecular fraction of the gas traced by ArH+ to lie below 2x10^-2^ with a median value of 8.8x10^-4^. Combined, our observations of ArH+, OH+, H_2_O+ and CH probe different regimes of the interstellar medium, from diffuse atomic to diffuse and translucent molecular clouds. Over Galactic scales, we see that the distribution of N(ArH+) is associated with that of N(H), particularly in the inner Galaxy (within 7 kpc of the Galactic center) with potentially even contributions from the warm neutral medium phase of atomic gas at larger galactocentric distances. We derive an average ortho-to-para ratio for H_2_O+ of 2.1+/-1.0, which corresponds to a nuclear spin temperature of 41K, consistent with the typical gas temperatures of diffuse clouds.
The study of noble gas compounds has gained renewed interest thanks to the recent detection of ArH^+^ in the interstellar medium (ISM). The analysis of physical-chemical conditions in the regions of the ISM where ArH^+^ is observed requires accurate collisional data of ArH^+^ with He, H_2_, electrons, and H. The main goals of this work are to compute the first three-dimensional potential energy surface (PES) to study the interaction of ArH^+^ with He, analyze the influence of the isotopic effects in the rate coefficients, and evaluate the rovibrational relaxation rates. Two ab initio grids of energy were computed at the coupled cluster with single, double, and perturbative triple excitations (CCSD(T)) level of theory using the augmented correlation consistent polarized quadruple, and quintuple zeta basis sets (aug-cc-pVQZ, and aug-cc-pV5Z) and a grid at the complete basis set limit was determined. The analytical representation of the PES was performed using the reproducing kernel Hilbert space (RKHS). The dynamics of the system was studied using the close coupling method. The differences in the rate coefficients for the isotopes ^36^ArH^+^, ^38^ArH^+^, and ^40^ArH^+^ in collision with He are negligible. However, the rotational rates for the collision of ArD+ with He cannot be estimated from those for ArH^+^+He. Comparison with previous rates for the 36ArH++He collision showed discrepancies for |{Delta}j|>2, and in the case of high initial rotational states of 36ArH+ differences were found even for |{Delta}j|=1. The rates for transitions between different vibrational states were also examined. Finally, new sets of rotational rates for ^36^ArH^+^+He and ^36^ArD^+^+He are reported.
The catalogue ARIHIP has been constructed by selecting the 'best
data' for a given star from combinations of HIPPARCOS data with Boss'
GC and/or the Tycho-2 catalogue as well as the FK6. It provides 'best
data' for 90 842 stars with a typical mean error of 0.89 mas/year
(about a factor of 1.3 better than Hipparcos for this sample of
stars).
This service provides the data for the TGAS catalogue (Tycho-Gaia Astrometric Solution ; a subset of the Gaia DR1 catalogue providing parallaxes and proper motions from Tycho2 for a little more than 2 million sources).
This service provides Gaia data (currently DR1, DR2 and EDR3), with full-sky catalogues of high-precision positions down to about 20 mag, as a mirror of the original ESA archive with extra features (e.g., tables and column metadata).
We present the Arizona CDFS Environment Survey (ACES), a recently completed spectroscopic redshift survey of the Chandra Deep Field-South (CDFS) conducted using the Inamori-Magellan Areal Camera and Spectrograph on the Magellan-Baade telescope. In total, the survey targeted 7277 unique sources down to a limiting magnitude of R_AB_=24.1, yielding 5080 secure redshifts across the ~30'x30' extended CDFS region. The ACES data set delivers a significant increase to both the spatial coverage and the sampling density of the spectroscopic observations in the field. Combined with previously published spectroscopic redshifts, ACES now creates a highly complete survey of the galaxy population at R<23, enabling the local galaxy density (or environment) on relatively small scales (~1Mpc) to be measured at z<1 in one of the most heavily studied and data-rich fields in the sky. Here, we describe the motivation, design and implementation of the survey and present a preliminary redshift and environment catalogue. In addition, we utilize the ACES spectroscopic redshift catalogue to assess the quality of photometric redshifts from both the COMBO-17 and Multiwavelength Survey by Yale-Chile imaging surveys of the CDFS.
![ARIHIP is licensed under the `Creative Commons Attribution 4.0 License <http://creativecommons.org/licenses/by/4.0/>`_ .. image:: /static/img/ccby.png :alt: [CC-BY]](/registry-search/?f%5Brights_facet%5D%5B%5D=ARIHIP+is+licensed+under+the+%60Creative+Commons+Attribution+4.0+License+%3Chttp%3A%2F%2Fcreativecommons.org%2Flicenses%2Fby%2F4.0%2F%3E%60_%0A%0A..+image%3A%3A+%2Fstatic%2Fimg%2Fccby.png%0A+++%3Aalt%3A+%5BCC-BY%5D%0A%0A&f%5Btype_facet%5D%5B%5D=Catalog){kind=link}