Letter to the Editor

Star formation triggered by H II regions in our Galaxy^*

First results for N49 from the Herschel infrared survey of the Galactic plane

¹ Laboratoire d'Astrophysique de Marseille (UMR 6110 CNRS & Université de Provence), 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France, e-mail: annie.zavagno@oamp.fr
² Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD, UK
³ Center for Astrophysics and Space Astronomy Department of Astrophysical and Planetary Sciences 389 UCB Boulder Colorado, USA
⁴ Spitzer Postdoctoral Fellow, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, 02138, USA
⁵ School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK
⁶ Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁷ ESO, Karl Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁸ NASA Herschel Science Center, IPAC, Caltech, Pasadena, CA 91125, USA
⁹ INAF-IFSI, Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁰ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF24 3AA, UK
¹¹ Dipartimento di Fisica, Università di Roma 2 “Tor Vergata”, Rome, Italy
¹² ASI Science Data Center, 00044 Frascati (Rome), Italy

Received: 30 March 2010
Accepted: 12 April 2010

Abstract

Context. It has been shown that by means of different physical mechanisms the expansion of H ii regions can trigger the formation of new stars of all masses. This process may be important to the formation of massive stars but has never been quantified in the Galaxy.

Aims. We use Herschel-PACS and -SPIRE images from the Herschel infrared survey of the Galactic plane, Hi-GAL, to perform this study.

Methods. We combine the Spitzer-GLIMPSE and -MIPSGAL, radio-continuum and submillimeter surveys such as ATLASGAL with Hi-GAL to study young stellar objects (YSOs) observed towards Galactic H ii regions. We select a representative H ii region, N49, located in the field centered on l = 30°observed as part of the Hi-GAL science demonstration phase, to demonstrate the importance Hi-GAL will have to this field of research.

Results. Hi-GAL PACS and SPIRE images reveal a new population of embedded young stars, coincident with bright ATLASGAL condensations. The Hi-GAL images also allow us, for the first time, to constrain the physical properties of the newly formed stars by means of fits to their spectral energy distribution. Massive young stellar objects are observed at the borders of the N49 region and represent second generation massive stars whose formation has been triggered by the expansion of the ionized region.

Conclusions. The first Hi-GAL images obtained using PACS and SPIRE have demonstrated the capability to investigate star formation triggered by H ii regions. With radio, submillimeter, and shorter wavelength infrared data from other surveys, the Hi-GAL images reveal young massive star-forming clumps surrounding the perimeter of the N49 H ii generated bubble. Hi-GAL enables us to detect a population of young stars at different evolutionary stages, cold condensations only being detected in the SPIRE wavelength range. The far IR coverage of Hi-GAL strongly constrains the physical properties of the YSOs. The large and unbiased spatial coverage of this survey offers us a unique opportunity to lead, for the first time, a global study of star formation triggered by H ii regions in our Galaxy.