2014A&A...566A..29S


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.04CEST01:16:51

2014A&A...566A..29S - Astronomy and Astrophysics, volume 566A, 29-29 (2014/6-1)

Ubiquitous argonium (ArH+) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas.

SCHILKE P., NEUFELD D.A., MUELLER H.S.P., COMITO C., BERGIN E.A., LIS D.C., GERIN M., BLACK J.H., WOLFIRE M., INDRIOLO N., PEARSON J.C., MENTEN K.M., WINKEL B., SANCHEZ-MONGE A., MOELLER T., GODARD B. and FALGARONE E.

Abstract (from CDS):

We describe the assignment of a previously unidentified interstellar absorption line to ArH+ and discuss its relevance in the context of hydride absorption in diffuse gas with a low H2 fraction. The confidence of the assignment to ArH+ is discussed, and the column densities are determined toward several lines of sight. The results are then discussed in the framework of chemical models, with the aim of explaining the observed column densities. We fitted the spectral lines with multiple velocity components, and determined column densities from the line-to-continuum ratio. The column densities of ArH+ were compared to those of other species, tracing interstellar medium (ISM) components with different H2 abundances. We constructed chemical models that take UV radiation and cosmic ray ionization into account. Thanks to the detection of two isotopologues, 36ArH+ and 38ArH+, we are confident about the carrier assignment to ArH+. NeH+ is not detected with a limit of [NeH+]/[ArH+]≤0.1. The derived column densities agree well with the predictions of chemical models. ArH+ is a unique tracer of gas with a fractional H2 abundance of 10–4-10–3 and shows little correlation to H2O+, which traces gas with a fractional H2 abundance of ≃0.1. A careful analysis of variations in the ArH+, OH+, H2O+, and HF column densities promises to be a faithful tracer of the distribution of the H2 fractional abundance by providing unique information on a poorly known phase in the cycle of interstellar matter and on its transition from atomic diffuse gas to dense molecular gas traced by CO emission. Abundances of these species put strong observational constraints upon magnetohydrodynamical (MHD) simulations of the interstellar medium, and potentially could evolve into a tool characterizing the ISM. Paradoxically, the ArH+ molecule is a better tracer of almost purely atomic hydrogen gas than Hi itself, since Hi can also be present in gas with a significant molecular content, but ArH+ singles out gas that is >99.9% atomic.

Abstract Copyright:

Journal keyword(s): astrochemistry - line: identification - molecular processes - ISM: abundances - ISM: molecules - ISM: structure

Simbad objects: 16

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Number of rows : 16

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 M 1 SNR 05 34 31.94 +22 00 52.2           ~ 5594 4
2 NGC 4355 Sy2 12 26 54.628 -00 52 39.51   14.21 13.37     ~ 404 2
3 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2679 4
4 NAME Nor Arm PoG 16 00 -50.0           ~ 338 0
5 NAME Gal Center reg 17 45 40.04 -29 00 28.1           ~ 11533 0
6 NAME Sgr B2 (North) Rad 17 47 20.2 -28 22 21           ~ 514 1
7 NAME Sgr B2 MoC 17 47 20.4 -28 23 07           ~ 1909 1
8 NAME Sgr B2 Main Rad 17 47 20.5 -28 23 06           ~ 331 1
9 W 31c HII 18 10 29.1 -19 56 05           ~ 301 0
10 OH 34.26 +0.15 SFR 18 53 18.54 +01 14 57.9           ~ 460 0
11 NAME Sgr Arm PoG 19 00 -30.0           ~ 523 1
12 W 49n HII 19 10 13.2 +09 06 12           ~ 411 3
13 W 49 SFR 19 10 20 +09 07.7           ~ 508 1
14 NAME W 51 IRS 1 PoC 19 23 41.9 +14 30 36           ~ 96 0
15 W 51 SNR 19 23 50 +14 06.0           ~ 1143 1
16 NAME Scutum Spiral Arm PoG ~ ~           ~ 275 0

    Equat.    Gal    SGal    Ecl

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2020.07.04-01:16:51

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