Journal Article

Parsec-scale SiO emission in an infrared dark cloud

I. Jiménez-Serra, P. Caselli, J. C. Tan, A. K. Hernandez, F. Fontani, M. J. Butler and S. van Loo

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 1, pages 187-196
Published in print July 2010 | ISSN: 0035-8711
Published online July 2010 | e-ISSN: 1365-2966 | DOI:
Parsec-scale SiO emission in an infrared dark cloud

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We present high-sensitivity 2 × 4 arcmin2 maps of the J= 2→1 rotational lines of SiO, CO, 13CO and C18O, observed towards the filamentary infrared dark cloud (IRDC) G035.39−00.33. Single-pointing spectra of the SiO J= 2→1 and J= 3→2 lines towards several regions in the filament are also reported. The SiO images reveal that SiO is widespread along the IRDC (size ≥2 pc), showing two different components: one bright and compact arising from three condensations (N, E and S) and the other weak and extended along the filament. While the first component shows broad lines (linewidths of ∼4–7 km s−1) in both SiO J= 2→1 and SiO J= 3→2, the second one is only detected in SiO J= 2→1 and has narrow lines (∼0.8 km s−1). The maps of CO and its isotopologues show that low-density filaments are intersecting the IRDC and appear to merge towards the densest portion of the cloud. This resembles the molecular structures predicted by flow-driven, shock-induced and magnetically-regulated cloud formation models. As in outflows associated with low-mass star formation, the excitation temperatures and fractional abundances of SiO towards N, E and S increase with velocity from ∼6 to 40 K and from ∼10−10 to ≥10−8, respectively, over a velocity range of ∼7 km s−1. Since 8 μm and 24 μm sources and/or extended 4.5 μm emission are detected in N, E and S, broad SiO is likely produced in outflows associated with high-mass protostars. The excitation temperatures and fractional abundances of the narrow SiO lines, however, are very low (∼9 K and ∼10−11, respectively), and consistent with the processing of interstellar grains by the passage of a shock with vs∼ 12 km s−1. This emission could be generated (i) by a large-scale shock, perhaps remnant of the IRDC formation process, (ii) by decelerated or recently processed gas in large-scale outflows driven by 8- and 24-μm sources or (iii) by an undetected and widespread population of lower mass protostars. High-angular-resolution observations are needed to disentangle between these three scenarios.

Keywords: stars: formation; ISM: individual objects: G035.39−00.33; ISM: molecules

Journal Article.  7587 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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