Volume 542, June 2012
|Number of page(s)||27|
|Section||Interstellar and circumstellar matter|
|Published online||25 May 2012|
1 Laboratoire d’Astrophysique de Marseille UMR 6110, CNRS, Université de Provence, 38 rue F. Joliot-Curie, 13388 Marseille, France
2 Institut d’Astrophysique Spatiale, UMR 8617, CNRS, Université Paris-Sud 11, 91405 Orsay, France
3 Laboratoire AIM Paris-Saclay, CEA/DSMCNRS Université Paris Diderot, IRFU/Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France
4 Centre d’études spatiales des rayonnements (CESR), Université de Toulouse (UPS), CNRS, UMR 5187, 9 avenue du colonel Roche, 31028 Toulouse Cedex 4, France
5 CNRS/INSU, Laboratoire d’Astrophysique de Bordeaux, UMR 5804, BP 89, 33271 Floirac Cedex, France
6 Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
Received: 16 May 2011
Accepted: 23 March 2012
Context. Because of their relatively simple morphology, “bubble” H II regions have been instrumental to our understanding of star formation triggered by H II regions. With the far-infrared (FIR) spectral coverage of the Herschel satellite, we can access the wavelengths where these regions emit the majority of their energy through their dust emission.
Aims. We wish to learn about the dust temperature distribution in and surrounding bubble H II regions and to calculate the mass and column density of regions of interest, in order to better understand ongoing star formation. Additionally, we wish to determine whether and how the spectral index of the dust opacity, β, varies with dust temperature. Any such relationship would imply that dust properties vary with environment.
Methods. Using aperture photometry and fits to the spectral energy distribution, we determine the average temperature, β-value, and mass for regions of interest within eight bubble H II regions. Additionally, we compute maps of the dust temperature and column density.
Results. At Herschel wavelengths (70 μm to 500 μm), the emission associated with H II regions is dominated by the cool dust in their photodissociation regions (PDRs). We find average dust temperatures of 26 K along the PDRs, with little variation between the H II regions in the sample, while local filaments and infrared dark clouds average 19 K and 15 K respectively. Higher temperatures lead to higher values of the Jeans mass, which may affect future star formation. The mass of the material in the PDR, collected through the expansion of the H II region, is between ~300 M⊙ and ~ 10 000 M⊙ for the H II regions studied here. These masses are in rough agreement with the expected masses swept up during the expansion of the H II regions. Approximately 20% of the total FIR emission is from the direction of the bubble central regions. This suggests that we are detecting emission from the “near-side” and “far-side” PDRs along the line of sight and that bubbles are three-dimensional structures. We find only weak support for a relationship between dust temperature and β, of a form similar to that caused by noise and calibration uncertainties alone.
Key words: stars: formation / ISM: bubbles / dust, extinction / Hii regions / photon-dominated region (PDR) / infrared: ISM
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2012
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