Letter to the Editor

Galactic cold cores: Herschel study of first Planck detections ^*,**

¹ Department of Physics, F00014, University of Helsinki, Finland e-mail: mika.juvela@helsinki.fi
² Observatory, University of Helsinki, Finland 1
³ CESR, Observatoire Midi-Pyrénées (CNRS-UPS), Université de Toulouse, BP 44346, 31028 Toulouse Cedex 04, France
⁴ IPAC, Caltech, Pasadena
⁵ Loránd Eötvös University, Department of Astronomy, Pázmány P.s. 1/a, 1117 Budapest, Hungary (OTKA K62304)
⁶ Laboratoire AIM, CEA/DSM - INSU/CNRS - Université Paris Diderot,IRFU/SAp CEA-Saclay, 91191 Gif-sur-Yvette, France
⁷ Laboratoire d'Astrophysique de Marseille, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
⁸ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
⁹ LPSC, Université Joseph Fourier Grenoble I, CNRS/IN2P3, Institut National Polytechnique de Grenoble, 53 Avenue des Martyrs, 38026 Grenoble Cedex, France
¹⁰ University of Toronto, CITA, Canada
¹¹ LERMA & UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
¹² INAF/IASF, Bologna, Italy

Received: 31 March 2010
Accepted: 20 April 2010

Abstract

Context. We present the first results from the project Galactic cold cores, where the cold interstellar clouds detected by the Planck satellite are studied with Herschel photometric observations. The final Planck catalogue is expected to contain several thousand sources. The Herschel observations during the science demonstration phase provided the first glimpse into the nature of these sources.

Aims. The main goal of the project is to derive the physical properties of the cold core population revealed by Planck. We examine three fields and confirm the Planck detections with Herschel data, which we also use to establish the evolutionary stage of the identified cores.

Methods. We study the morphology and spectral energy distribution of the sources using the combined wavelength coverage of Planck and Herschel. The dust colour temperatures and emissivity indices are determined. The masses of the cores are determined with distance estimates which are taken from the literature and are confirmed by kinematic and extinction information.

Results. The observations reveal extended regions of cold dust with dust colour temperatures down to T_dust ~ 11 K. The fields represent different evolutionary stages ranging from a quiescent, cold filament in Musca to regions of active star formation in Cepheus.

Conclusions. The Herschel observations confirm that the all-sky survey of Planck is capable of making a large number of new cold core detections. Our results suggest that many of the sources may already have left the pre-stellar phase or are at least closely associated with active star formation. High-resolution Herschel observations are needed to establish the true nature of the Planck detections.