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Title: New constraints on the sulfur reservoir in the dense interstellar medium provided by Spitzer observations of S I in shocked gas

We present observations of fine-structure line emission of atomic sulfur, iron, and rotational lines of molecular hydrogen in shocks associated with several Class 0 protostars obtained with the Infrared Spectrograph of the Spitzer Space Telescope. We use these observations to investigate the 'missing sulfur problem', that significantly less sulfur is found in dense regions of the interstellar medium (ISM) than in diffuse regions. For sources where the sulfur fine-structure line emission is co-spatial with the detected molecular hydrogen emission and in the presence of weak iron emission, we derive sulfur and H{sub 2} column densities for the associated molecule-dominated C-shocks. We find the S I abundance to be ≳5%-10% of the cosmic sulfur abundance, indicating that atomic sulfur is a major reservoir of sulfur in shocked gas. This result suggests that in the quiescent dense ISM sulfur is present in some form that is released from grains as atoms, perhaps via sputtering, within the shock.
Authors:
;  [1] ;  [2] ;  [3]
  1. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States)
  2. UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041 (France)
  3. Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac (France)
Publication Date:
OSTI Identifier:
22348418
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ATOMS; DENSITY; EMISSION; FINE STRUCTURE; HYDROGEN; IRON; LIMITING VALUES; MOLECULES; PROTOSTARS; SPACE; SULFUR; TELESCOPES