SiO: Not the perfect outflow tracer

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 H 13 CO + emission with high angular resolution. SiO is known to trace shocked gas, which is often associated with young energetic outflows. With the H 13 CO + 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 H 13 CO + 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 H 2 data. Results. The SiO observations do not trace the previously in CO and H 2 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 H 2 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.

Methanol and water maser observations separate disc and outflow sources in IRAS 19410+2336

“…5) Beuther et al (2003). The peak of the thermal SiO clump is shown by a square (measured in a beam size of 4") (Widmann et al 2016). This shows that the 12-GHz masers observed by Minier et al (2000), have an angular separation of ∼ 0.…”

“…Figure 6 (right) shows the positions of other emission detected in this region.The thermal SiO (Widmann et al 2016) was observed with a 4-arcsec beam, larger than the total maser extent. Millimetre source mm1, position accuracy 0.…”

“…The line widths of the SiO detected by Widmann et al (2016) in the region (typically 18 km s −1 ) along with a Gaussian profile, but with an additional signal in the line wings, strongly suggests that SiO traces dynamical gas in jets and/or outflows (Widmann et al 2016).…”

“…The outflow activity in IRAS 19410+2336 has been studied extensively by Beuther et al (2003); Martín-Hernández et al (2008) and Widmann et al (2016). Beuther et al (2003) observed CO (J = 1-0) in addition to the 2.6 mm continuum using the IRAM 30 m telescope and the Plateau de Bure interferometer, and the H2 line at 2.12 µm, using the Calar Alto 3.5 m telescope.…”

“…On the other hand, the core accretion model, which is considered as a scaled-up version of low-mass star formation, suggests well-collimated outflows similar to those associated with low mass protostars (Widmann et al 2016, and references therein). According to Arce et al (2007) the opening angles for well-collimated outflows in massive star forming regions are between 25 • and 30 • .…”