Gas phase Elemental abundances in Molecular cloudS (GEMS). IV. Observational results and statistical trends

Author(s): M. Rodriguez-Baras, A. Fuente, P. Rivière-Marichalar, D. Navarro-Almaida, P. Caselli, Alvaro Hacar Gonzalez
Abstract: 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 T_k ~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⁺, H¹³CN, and HNC; and (3) the S-bearing molecules. The abundances of the CO isotopologs increase with the gas kinetic temperature until T_K ~ 15 K. For higher temperatures, the abundance remains constant with a scatter of a factor of ~3. The abundances of H¹³CO+, HC¹⁸O⁺, H¹³CN, 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 H¹³CO⁺/H¹³CN abundance ratios as chemical diagnostics of star formation in external galaxies.
Organisation(s): Department of Astrophysics
External organisation(s): Observatorio Astronómico Nacional (OAN-IGN), Max-Planck-Institut für extraterrestrische Physik
Journal: Astronomy & Astrophysics
Volume: 648
No. of pages: 26
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/202040112
Publication date: 04-2021
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/08b6cb9b-766b-43b0-ba25-978f62d05564

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