Tracing extended low-velocity shocks through SiO emission

Case study of the W43-MM1 ridge^⋆

¹ Laboratoire AIM Paris-Saclay, CEA/IRFU−CNRS/INSU−Université Paris Diderot, Service d’Astrophysique, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
e-mail: fabien.louvet@cea.fr
² Departamento de Astronomia de Chile, Universidad de Chile, 1058 Santiago, Chile
³ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁴ LERMA, UMR 8112 du CNRS, Observatoire de Paris, École Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France
⁵ ALMA Chile Observatory, National Observatory of Japan, 181-8588 Tokyo, Japan
⁶ School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁷ Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
⁸ Joint ALMA observatory, 3107 Santiago, Chile
⁹ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin d’Hères, France

Received: 9 June 2016
Accepted: 25 July 2016

Abstract

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 low-velocity 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.