A submillimetre search for pre- and proto-brown dwarfs in Chamaeleon II

¹ European Southern Observatory, Karl Schwarzschild Str 2, D-85748 Garching bei München, Germany
e-mail: idegrego@eso.org
² Joint ALMA office, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
³ Dpto. Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC Campus, PO Box 78, 28691 Villanueva de la Cañada, Spain
⁴ Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁵ Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, 5030 Casilla, Valparaíso, Chile
⁶ Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, PO Box 3-72, 58090 Morelia, Michoacán, México
⁷ Academia Sinica, Institute of Astronomy and Astrophysics, PO Box 23-141, 106 Taipei, Taiwan
⁸ Herschel Science Centre, ESAC-ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁹ Depto. Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain

Received: 6 May 2014
Accepted: 1 December 2015

Abstract

Context. The Chamaeleon II molecular cloud is an active star-forming region that offers an excellent opportunity to study the formation of brown dwarfs in the southern hemisphere.

Aims. Our aims are to identify a population of pre- and proto-brown dwarfs (5σ mass limit threshold of ~0.015 M_⊙) and provide information on the formation mechanisms of substellar objects.

Methods. We performed high sensitivity observations at 870 μm using the LABOCA bolometer at the APEX telescope towards an active star-forming region in Chamaeleon II. The data are complemented by an extensive multiwavelength catalogue of sources, which covers the optical to the far-infrared, to study the nature of the LABOCA detections.

Results. We detect 15 cores at 870 μm, and 11 of them show masses in the substellar regime. The most intense objects in the surveyed field correspond to the submillimetre counterparts of the well-known young stellar objects DK Cha and IRAS 12500-7658. We identify a possible proto-brown dwarf candidate (ChaII-APEX-L) with IRAC emission at 3.6 and 4.5 μm.

Conclusions. Our analysis indicates that most of the spatially resolved cores are transient, and that the point-like starless cores in the substellar regime (with masses between 0.016 M_⊙ and 0.066 M_⊙) could be pre-brown dwarfs cores that are gravitationally unstable if they have radii less than 220 AU to 907 AU (1.2′′ to 5′′ at 178 pc), respectively, for different masses. ALMA observations will be key to revealing the energetic state of these pre-brown dwarfs candidates.