Letter to the Editor

Recent star formation in the Lupus clouds as seen by Herschel^⋆,⋆⋆

¹ Istituto di Astrofisica e Planetologia Spaziali (INAF-IAPS), via del Fosso del Cavaliere 100, 00133 Roma, Italy
e-mail: kazi.rygl@inaf.it
² Laboratoire AIM Paris-Saclay, CEA/IRFU CNRS/INSU Université Paris Diderot, 91191 Gif-sur-Yvette, France
³ CESR, Observatoire Midi-Pyrénées (CNRS-UPS), Université de Toulouse, BP 44346, 31028 Toulouse, France
⁴ Rutherford Appleton LIbrary, Chilton, Didcot, OX11 0NL, UK
⁵ Department of Physics and Astronomy, Open University, Milton Keynes, UK
⁶ University of Athens, Department of Astrophysics, Astronomy and Mechanics, Faculty of Physics, Panepistimiopolis, 15784 Zografos, Athens, Greece
⁷ CNRS/INSU, Laboratoire d’Astrophysique de Bordeaux UMR 5904, BP 89, 33271 Floirac, France
⁸ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁹ Department of Physics and Astronomy, University of Victoria, PO Box 355, STN CSC, Victoria BC, V8W 3P6, Canada
¹⁰ National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria BC, V9E 2E7, Canada
¹¹ Canadian Institute for Theoretical Astrophysics (CITA), University of Toronto, 60 St. George Street, Toronto, ON, M5S 3H8, Canada
¹² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 87548 Garching bei München, Germany
¹³ INAF-Osservatorio Astrofisico di Arcetri, Large E. Fermi 5, 50125 Firenze, Italy
¹⁴ Jeremiah Horrocks Institute, University of Central Lancashire, PR1 2HE, UK

Received: 30 April 2012
Accepted: 16 November 2012

Abstract

We present a study of the star formation histories of the Lupus I, III, and IV clouds using the Herschel 70–500 μm maps obtained by the Herschel Gould Belt Survey Key Project. By combining the new Herschel data with the existing Spitzer catalog we obtained an unprecedented census of prestellar sources and young stellar objects in the Lupus clouds, which allowed us to study the overall star formation rate (SFR) and efficiency (SFE). The high SFE of Lupus III, its decreasing SFR, and its large number of pre-main sequence stars with respect to proto- and prestellar sources, suggest that Lupus III is the most evolved cloud, and after having experienced a major star formation event in the past, is now approaching the end of its current star-forming cycle. Lupus I is currently undergoing a large star formation event, apparent by the increasing SFR, the large number of prestellar objects with respect to more evolved objects, and the high percentage of material at high extinction (e.g., above A_V ≈ 8   mag). Also Lupus IV has an increasing SFR; however, the relative number of prestellar sources is much lower, suggesting that its star formation has not yet reached its peak.