Gas phase Elemental abundances in Molecular cloudS (GEMS)
Astronomy and Astrophysics, vol. 670, pp. A114
Abstract
Context. Gas phase Elemental abundances in molecular CloudS (GEMS) is an IRAM 30-m Large Program aimed at determining the elemental abundances of carbon (C), oxygen (O), nitrogen (N), and sulfur (S) in a selected set of prototypical star-forming filaments. In particular, the elemental abundance of S remains uncertain by several orders of magnitude, and its determination is one of the most challenging goals of this program. Aims. This paper aims to constrain the sulfur elemental abundance in Taurus, Perseus, and Orion A based on the GEMS molecular database. The selected regions are prototypes of low-mass, intermediate-mass, and high-mass star-forming regions, respectively, providing useful templates for the study of interstellar chemistry. Methods. We have carried out an extensive chemical modeling of the fractional abundances of CO, HCO + , HCN, HNC, CS, SO, H 2 S, OCS, and HCS + to determine the sulfur depletion toward the 244 positions in the GEMS database. These positions sample visual extinctions from A V ~ 3 mag to >50 mag, molecular hydrogen densities ranging from a few × 10 3 cm −3 to 3 × 10 6 cm −3 , and T k ~ 10–35 K. We investigate the possible relationship between sulfur depletion and the grain charge distribution in different environments. Results. Most of the positions in Taurus and Perseus are best fitted assuming early-time chemistry, t = 0.1 Myr, ζ H 2 ~ (0.5−1) × 10 −16 s −1 , and [S/H] ~ 1.5 × 10 −6 . On the contrary, most of the positions in Orion are fitted with t = 1 Myr and ζ H 2 ~ 10 −17 s −1 . Moreover, ~40% of the positions in Orion are best fitted assuming the undepleted sulfur abundance, [S/H] ~ 1.5 × 10 −5 . We find a tentative trend of sulfur depletion increasing with density. Conclusions. Our results suggest that sulfur depletion depends on the environment. While the abundances of sulfur-bearing species are consistent with undepleted sulfur in Orion, a depletion factor of ~20 is required to explain those observed in Taurus and Perseus. We propose that differences in the grain charge distribution might explain these variations. Grains become negatively charged at a visual extinction of A V ~ 3.5 mag in Taurus and Perseus. At this low visual extinction, the S + abundance is high, X (S + ) > 10 −6 , and the electrostatic attraction between S + and negatively charged grains could contribute to enhance sulfur depletion. In Orion, the net charge of grains remains approximately zero until higher visual extinctions ( A V ~ 5.5 mag), where the abundance of S + is already low because of the higher densities, thus reducing sulfur accretion. The shocks associated with past and ongoing star formation could also contribute to enhance [S/H].
Authors 21
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Affiliation as printed
Observatorio Astronomico Nacional (OAN), Alfonso XII 3, 28014 Madrid, Spain
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Affiliation as printed
Observatorio Astronomico Nacional (OAN), Alfonso XII 3, 28014 Madrid, Spain
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Universidad Complutense de Madrid · Spanish National Observatory
Affiliation as printed
Departamento de Física de la Tierra y Astrofísica, Facultad de CC. Matemáticas, Universidad Complutense de Madrid, Plaza de las Ciencias 3, 28040 Madrid, Spain
Observatorio Astronomico Nacional (OAN), Alfonso XII 3, 28014 Madrid, Spain
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Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Centre for Astrochemical Studies, Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
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Centre National de la Recherche Scientifique · Laboratoire d'Astrophysique de Bordeaux
Affiliation as printed
Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
Laboratoire d'astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
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Affiliation as printed
Observatorio Astronomico Nacional (OAN), Alfonso XII 3, 28014 Madrid, Spain
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Affiliation as printed
Observatorio Astronomico Nacional (OAN), Alfonso XII 3, 28014 Madrid, Spain
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Commissariat à l'Énergie Atomique et aux Énergies Alternatives · Université Paris-Saclay · Astrophysique, Instrumentation et Modélisation · CEA Paris-Saclay
Affiliation as printed
Université Paris-Saclay, CEA, AIM, Département d’Astrophysique (DAp), 91191 Gif-sur-Yvette, France
Université Paris-Saclay, CEA, AIM, Département d'Astrophysique (DAp), 91191 Gif-sur-Yvette, France
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Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · École Normale Supérieure - PSL · Sorbonne Université · Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères · Université Pierre-et-Marie-Curie
Affiliation as printed
LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR8112, Place Janssen, 92190, Meudon Cedex, France
Observatoire de Paris, PSL Research University, CNRS, École Normale Supérieure, Sorbonne Université, UPMC Univ. Paris 6, 75005 Paris, France
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Institut de Radioastronomie Millimétrique · Instituto de Radioastronomía Milimétrica
Affiliation as printed
Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France
Instituto de Radioastronomía Milimétrica (IRAM), Av. Divina Pastora 7, Nucleo Central, 18012 Granada, Spain
Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin-d'Hères, France
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Affiliation as printed
Observatorio Astronomico Nacional (OAN), Alfonso XII 3, 28014 Madrid, Spain
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Instituto de Física Fundamental
Affiliation as printed
Instituto de Física Fundamental (CSIC), Calle Serrano 121–123, 28006 Madrid, Spain
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Consejo Superior de Investigaciones Científicas · Centro de Astrobiología
Affiliation as printed
Centro de Astrobiología (CSIC-INTA), Ctra. de Ajalvir, km 4, Torrejon de Ardoz, 28850, Madrid, Spain
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Centre National de la Recherche Scientifique · Institut des Sciences Moléculaires
Affiliation as printed
Institut des Sciences Moléculaires (ISM), CNRS, Univ. Bordeaux, 351 cours de la Libération, 33400 Talence, France
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Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Centre for Astrochemical Studies, Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
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Center for Astrophysics Harvard & Smithsonian
Affiliation as printed
Center for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
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Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Centre for Astrochemical Studies, Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
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Instituto de Física Fundamental
Affiliation as printed
Instituto de Física Fundamental (CSIC), Calle Serrano 121–123, 28006 Madrid, Spain
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Consejo Superior de Investigaciones Científicas · Centro de Astrobiología
Affiliation as printed
Centro de Astrobiología (CSIC-INTA), Ctra. de Ajalvir, km 4, Torrejon de Ardoz, 28850, Madrid, Spain
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Stéphanie M. Cazaux Aachen
Leiden University · Delft University of Technology
Affiliation as printed
Faculty of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands
University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
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Affiliation as printed
Observatorio Astronomico Nacional (OAN), Alfonso XII 3, 28014 Madrid, Spain
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