Issue |
A&A
Volume 648, April 2021
|
|
---|---|---|
Article Number | A120 | |
Number of page(s) | 26 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202040112 | |
Published online | 26 April 2021 |
Gas phase Elemental abundances in Molecular cloudS (GEMS)
IV. Observational results and statistical trends
1
Observatorio Astronómico Nacional (OAN),
Alfonso XII, 3,
28014
Madrid, Spain
e-mail: m.rodriguez@oan.es
2
Centre for Astrochemical Studies, Max-Planck-Institute for Extraterrestrial Physics,
Giessenbachstrasse 1,
85748
Garching, Germany
3
Observatoire de Paris, PSL Research University, CNRS, École Normale Supérieure, Sorbonne Universités, UPMC Univ. Paris 06,
75005
Paris, France
4
Institut de Radioastronomie Millimétrique,
300 rue de la Piscine, Domaine Universitaire,
38406
Saint Martin d’Hères, France
5
LERMA, Observatoire de PARIS, PSL Research University, CNRS, Sorbonne Université,
92190
Meudon, France
6
Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire,
33615
Pessac, France
7
Harvard-Smithsonian Center for Astrophysics,
60 Garden St.,
Cambridge,
MA 02138, USA
8
Faculty of Aerospace Engineering, Delft University of Technology,
Delft, The Netherlands
9
University of Leiden,
PO Box 9513,
NL,
2300 RA
Leiden, The Netherlands
10
École Normale Supérieure de Lyon, CRAL, UMR CNRS 5574, Université Lyon I,
46 allée d’Italie,
69364
Lyon Cedex 07, France
11
Instituto de Física Fundamental (CSIC),
Calle Serrano 123,
28006
Madrid, Spain
12
Institut des Sciences Moléculaires (ISM), CNRS, Univ. Bordeaux,
351 cours de la Libération,
33400
Talence, France
13
Chalmers University of Technology, Department of Space,
Earth and Environment,
412 93
Gothenburg, Sweden
14
Centro de Astrobiología (CSIC-INTA),
Ctra. de Ajalvir, km 4,
Torrejón de Ardoz,
28850
Madrid, Spain
15
University of Vienna, Department of Astrophysics,
Tuerkenschanzstrasse 17,
1180
Vienna, Austria
16
Jeremiah Horrocks Institute, University of Central Lancashire,
Preston
PR1 2HE, UK
17
Observatorio de Yebes (IGN). Cerro de la Palera s/n,
19141
Yebes, Spain
18
Department of Physics, University of Helsinki,
PO Box 64,
00014
Helsinki, Finland
19
Institute of Physics I, University of Cologne,
Cologne, Germany
20
National Radio Astronomy Observatory,
520 Edgemont Rd.,
Charlottesville
VA 22901, USA
Received:
10
December
2020
Accepted:
10
February
2021
Gas phase Elemental abundances in Molecular CloudS (GEMS) is an IRAM 30 m Large Program designed to provide estimates of the S, C, N, and O depletions and gas ionization degree, X(e−), in a selected set of star-forming filaments of Taurus, Perseus, and Orion. Our immediate goal is to build up a complete and large database of molecular abundances that can serve as an observational basis for estimating X(e−) and the C, O, N, and S depletions through chemical modeling. We observed and derived the abundances of 14 species (13CO, C18O, HCO+, H13CO+, HC18O+, HCN, H13CN, HNC, HCS+, CS, SO, 34SO, H2S, and OCS) in 244 positions, covering the AV ~3 to ~100 mag, n(H2) ~ a few 103 to 106 cm−3, and Tk ~10 to ~30 K ranges in these clouds, and avoiding protostars, HII regions, and bipolar outflows. A statistical analysis is carried out in order to identify general trends between different species and with physical parameters. Relations between molecules reveal strong linear correlations which define three different families of species: (1) 13CO and C18O isotopologs; (2) H13CO+, HC18O+, H13 CN, and HNC; and (3) the S-bearing molecules. The abundances of the CO isotopologs increase with the gas kinetic temperature until TK ~ 15 K. For higher temperatures, the abundance remains constant with a scatter of a factor of ~3. The abundances of H13 CO+, HC18 O+, H13 CN, and HNC are well correlated with each other, and all of them decrease with molecular hydrogen density, following the law ∝ n(H2)−0.8 ± 0.2. The abundances of S-bearing species also decrease with molecular hydrogen density at a rate of (S-bearing/H)gas ∝ n(H2)−0.6 ± 0.1. The abundances of molecules belonging to groups 2 and 3 do not present any clear trend with gas temperature. At scales of molecular clouds, the C18O abundance is the quantity that better correlates with the cloud mass. We discuss the utility of the 13CO/C18O, HCO+/H13CO+, and H13 CO+/H13CN abundance ratios as chemical diagnostics of star formation in external galaxies.
Key words: astrochemistry / ISM: abundances / ISM: molecules / ISM: clouds / stars: formation / galaxies: ISM
© ESO 2021
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