The W43-MM1 mini-starburst ridge, a test for star formation efficiency models^⋆

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 Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA
³ Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St. Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK
⁴ OASU/LAB-UMR 5804, CNRS/INSU – Université Bordeaux 1, 2 rue de l’Observatoire, BP 89, 33270 Floirac, France
⁵ LERMA, UMR 8112 du CNRS, Observatoire de Paris, École Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France
⁶ Joint ALMA ObservatoryAlonso de Cordova 3107, 763 0355 Vitacura Santiago Chile
⁷ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d’Hères, France
⁸ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
⁹ School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
¹⁰ Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
¹¹ LERMA2, Observatoire de Paris, 61 Av. de l’Observatoire, 75014 Paris, France
¹² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹³ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada
¹⁴ California Institute of Technology, Pasadena CA 91125, USA
¹⁵ Sorbonne Universités, Université Pierre et Marie Curie, Paris 6, CNRS, Observatoire de Paris, UMR 8112, LERMA, Paris, France

Received: 9 February 2014
Accepted: 23 May 2014

Abstract

Context. Star formation efficiency (SFE) theories are currently based on statistical distributions of turbulent cloud structures and a simple model of star formation from cores. They remain poorly tested, especially at the highest densities.

Aims. We investigate the effects of gas density on the SFE through measurements of the core formation efficiency (CFE). With a total mass of ~2 × 10⁴ M_⊙, the W43-MM1 ridge is one of the most convincing candidate precursors of Galactic starburst clusters and thus one of the best places to investigate star formation.

Methods. We used high-angular resolution maps obtained at 3 mm and 1 mm within the W43-MM1 ridge with the IRAM Plateau de Bure Interferometer to reveal a cluster of 11 massive dense cores, and, one of the most massive protostellar cores known. A Herschel column density image provided the mass distribution of the cloud gas. We then measured the “instantaneous” CFE and estimated the SFE and the star formation rate (SFR) within subregions of the W43-MM1 ridge.

Results. The high SFE found in the ridge (~6% enclosed in ~8 pc³) confirms its ability to form a starburst cluster. There is, however, a clear lack of dense cores in the eastern part of the ridge, which may be currently assembling. The CFE and the SFE are observed to increase with volume gas density, while the SFR per free fall time steeply decreases with the virial parameter, α_vir. Statistical models of the SFR may describe the outskirts of the W43-MM1 ridge well, but struggle to reproduce its inner part, which corresponds to measurements at low α_vir. It may be that ridges do not follow the log-normal density distribution, Larson relations, and stationary conditions forced in the statistical SFR models.