Parsec-scale SiO emission in an infrared dark cloud

Abstract

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.

A MALT90 study of the chemical properties of massive clumps and filaments of infrared dark clouds

“…As supported by the observed line wings, SiO emission is probably caused by outflow activity which generates shocks releasing SiO into the gas phase. However, some of the widespread SiO emission could result from shocks associated with cloud formation as suggested in the IRDC G035.39-00.33 (Jiménez-Serra et al 2010). The SiO abundances derived for our clumps are mostly comparable to those seen in other IRDCs (Vasyunina et al 2011;Sanhueza et al 2012).…”

“…It is also worth noting that the submm peaks G1.87−SMM 28, 30, and 38 are coincident with the local SiO peak positions. Jiménez-Serra et al (2010) proposed that the extended SiO emission they observed along the filamentary IRDC G035.39-00.33 is the result of a low-velocity shock produced by colliding flows (see also Henshaw et al 2013). The widespread SiO emission could therefore originate in the cloud formation process instead of during star formation.…”

The Giant Molecular Cloud Environments of Infrared Dark Clouds

“…Theories involving production of dense gas in shocks have been supported by detection of large-scale SiO emission along IRDCs (Jiménez-Serra et al 2010;Nguyen-Lu'o'ng et al 2013). However, these studies focus only on a few individual clouds and are still confined to few-parsec scales in and around the filamentary molecular clouds.…”

SiO outflows in high-mass star forming regions: A potential chemical clock?

“…Motte et al 2007;Sakai et al 2010). However, an interesting recent study by Jiménez-Serra et al (2010) shows that the SiO emission towards the IR-dark cloud G35.39-0.33 is extended on parsec scale, suggesting widespread low-mass star formation. A&A 526, L2 (2011) Observations towards low-mass protostars so far point to an evolutionary picture in which jets are always associated with Class 0 objects (e.g.…”