Tracing extended low-velocity shocks through SiO emission case study of the W43-MM1 ridge
2016
Aims. Previous literature suggests that the densest structures in the interstellar medium form through colliding flows, but patent
evidence of this process is still missing. Recent literature proposes using SiO line emission to trace low-velocity shocks associated
with cloud formation through collision. In this paper we investigate the bright and extended SiO(2−1) emission observed along the
∼5 pc-long W43-MM1 ridge to determine its origin.
Methods. We used high angular resolution images of the SiO(2−1) and HCN(1−0) emission lines obtained with the IRAM plateau
de Bure (PdBI) interferometer and combined with data from the IRAM 30 m radiotelescope. These data were complemented by
a Herschel column density map of the region. We performed spectral analysis of SiO and HCN emission line profiles to identify
protostellar outflows and spatially disentangle two velocity components associated with low- and high-velocity shocks. Then, we
compared the low-velocity shock component to a dedicated grid of one-dimensional (1D) radiative shock models.
Results. We find that the SiO emission originates from a mixture of high-velocity shocks caused by bipolar outflows and lowvelocity
shocks. Using SiO and HCN emission lines, we extract seven bipolar outflows associated with massive dense cores previously
identified within the W43-MM1 mini-starburst cluster. Comparing observations with dedicated Paris-Durham shock models constrains
the velocity of the low-velocity shock component from 7 to 12 km s−1
.
Conclusions. The SiO arising from low-velocity shocks spreads along the complete length of the ridge. Its contribution represents at
least 45% and up to 100% of the total SiO emission depending on the area considered. The low-velocity component of SiO is most
likely associated with the ridge formation through colliding flows or cloud-cloud collision.
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