SiO: Not the perfect outflow tracer

Outflow studies of the massive star formation region IRAS 19410+2336^⋆

¹ Max Planck Institute for Astronomy Königstuhl 17 69117 Heidelberg Germany
e-mail: f.widmann@stud.uni-heidelberg.de
² I. Physikalisches Institut, University of Cologne, Zülpicher Strasse 77, 50937 Köln, Germany
³ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany

Received: 14 May 2015
Accepted: 24 February 2016

Abstract

Aims. Previous observations of the young massive star formation region IRAS 19410+2336 have revealed strong outflow activity with several interacting outflows. We aim to get a better understanding of the outflow activity in this region by observing the SiO and H¹³CO⁺ emission with high angular resolution. SiO is known to trace shocked gas, which is often associated with young energetic outflows. With the H¹³CO⁺ data, we intend to better understand the distribution of the quiescent gaseous component of the region.

Methods. The SiO observations in the J = 2–1 v = 0 transition and H¹³CO⁺J = 1–0 observations were performed by the Plateau de Bure Interferometer, combined with IRAM 30 m single-dish observations, in order to get the missing short-spacing information. We complement this new high-resolution observation with earlier CO and H₂ data.

Results. The SiO observations do not trace the previously in CO and H₂ identified outflows well. Although we identify regions of highly increased SiO abundance indicative of shock interaction, there are hardly any bipolar structures in the data. The southern part of the region, which exhibits strong H₂ emission, shows almost no SiO. The CO and SiO data show only weak similarities, and the main SiO emission lies between the two dominating dust clumps of the region.

Conclusions. Most SiO emission is likely to be a result of high-velocity shocks due to protostellar jets. However, this does not explain all the emission features and additional effects; for example, colliding gas flows at the interface of the two main regions may play an important role in the origin of the emission. The present SiO data show that several different effects can influence SiO emission, which makes the interpretation of SiO data more difficult than often assumed.