ALMA survey of massive cluster progenitors from ATLASGAL

Limited fragmentation at the early evolutionary stage of massive clumps^⋆

¹ Max Planck Institute for Radioastronomy, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: csengeri@mpifr-bonn.mpg.de
² OASU/LAB-UMR5804, CNRS, Université Bordeaux, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
³ Institut de Planétologie et d’Astrophysique de Grenoble, Univ. Grenoble Alpes – CNRS-INSU, BP 53, 38041 Grenoble Cedex 9, France
⁴ Laboratoire AIM Paris Saclay, CEA-INSU/CNRS-Université Paris Diderot, IRFU/SAp CEA-Saclay, 91191 Gif-sur-Yvette, France
⁵ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁶ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
⁷ Univ. Lyon, ENS de Lyon, Univ Lyon1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69007, Lyon, France
⁸ IRAM, 300 rue de la piscine, 38406 Saint-Martin-d’ Hères, France
⁹ School of Physics and Astronomy, University of Exeter, UK
¹⁰ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
¹¹ Astrophysics Research Institute, Liverpool John Moores University, UK
¹² Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Mexico
¹³ School of Physics & Astronomy, Cardiff University, UK
¹⁴ Departments of Astronomy and Physics, University of Florida, USA
¹⁵ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
¹⁶ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁷ IAPS–INAF, Via Fosso del Cavaliere, 100, 00133 Rome, Italy
¹⁸ School of Physical Sciences, University of Kent, Ingram Building, Canterbury, Kent CT2 7NH, UK

Received: 20 September 2016
Accepted: 1 March 2017

Abstract

The early evolution of massive cluster progenitors is poorly understood. We investigate the fragmentation properties from 0.3 pc to 0.06 pc scales of a homogenous sample of infrared-quiet massive clumps within 4.5 kpc selected from the ATLASGAL survey. Using the ALMA 7 m array we detect compact dust continuum emission towards all targets and find that fragmentation, at these scales, is limited. The mass distribution of the fragments uncovers a large fraction of cores above 40 M_⊙, corresponding to massive dense cores (MDCs) with masses up to ~400 M_⊙. Seventy-seven percent of the clumps contain at most 3 MDCs per clump, and we also reveal single clumps/MDCs. The most massive cores are formed within the more massive clumps and a high concentration of mass on small scales reveals a high core formation efficiency. The mass of MDCs highly exceeds the local thermal Jeans mass, and we lack the observational evidence of a sufficiently high level of turbulence or strong enough magnetic fields to keep the most massive MDCs in equilibrium. If already collapsing, the observed fragmentation properties with a high core formation efficiency are consistent with the collapse setting in at parsec scales.