Modeling and predicting the shape of the far-infrared to submillimeter emission in ultra-compact HII regions and cold clumps^⋆

¹ Université de Toulouse, UPS-OMP, IRAP, 31400 Toulouse, France
e-mail: deborah.paradis@irap.omp.eu
² CNRS, IRAP, 9 Av. du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
³ Infrared Processing Analysis Center, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA
⁴ Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7750, 11 rue de l’Université, 67000 Strasbourg, France
⁵ Space Research Institute, RAS, 84/32 Profsoyuznaya, 117810 Moscow, Russia
⁶ Space Telescope Science Institue, 3700 San Martin Dr, Baltimore, MD 21218, USA

Received: 29 August 2013
Accepted: 24 September 2014

Abstract

Context. Dust properties are very likely affected by the environment in which dust grains evolve. For instance, some analyses of cold clumps (7–17 K) indicate that the aggregation process is favored in dense environments. However, studying warm (30–40 K) dust emission at long wavelength (λ> 300 μm) has been limited because it is difficult to combine far infrared-to-millimeter (FIR-to-mm) spectral coverage and high angular resolution for observations of warm dust grains.

Aims. Using Herschel data from 70 to 500 μm, which are part of the Herschel infrared Galactic (Hi-GAL) survey combined with 1.1 mm data from the Bolocam Galactic Plane Survey (BGPS), we compared emission in two types of environments: ultra-compact HII (UCHII) regions, and cold molecular clumps (denoted as cold clumps). With this comparison we tested dust emission models in the FIR-to-mm domain that reproduce emission in the diffuse medium, in these two environments (UCHII regions and cold clumps). We also investigated their ability to predict the dust emission in our Galaxy.

Methods. We determined the emission spectra in twelve UCHII regions and twelve cold clumps, and derived the dust temperature (T) using the recent two-level system (TLS) model with three sets of parameters and the so-called T-β (temperature-dust emissivity index) phenomenological models, with β set to 1.5, 2 and 2.5.

Results. We tested the applicability of the TLS model in warm regions for the first time. This analysis indicates distinct trends in the dust emission between cold and warm environments that are visible through changes in the dust emissivity index. However, with the use of standard parameters, the TLS model is able to reproduce the spectral behavior observed in cold and warm regions, from the change of the dust temperature alone, whereas a T-β model requires β to be known.