On the importance of scattering at 8 μm: Brighter than you think

¹ LERMA & UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l’Observatoire, 75014 Paris, France
e-mail: charlene.lefevre@obspm.fr
² Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
³ Department of Physics, Applied Physics and Astronomy and New York Center for Astrobiology, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180, USA

Received: 19 July 2015
Accepted: 7 December 2015

Abstract

Context. Extinction and emission of dust models need for observational constraints to be validated. The coreshine phenomenon has already shown the importance of scattering in the 3 to 5 μm range and its ability to validate dust properties for dense cores.

Aims. We want to investigate whether scattering can also play a role at longer wavelengths and to place even tighter constraints on the dust properties.

Methods. We analyze the inversion of the Spitzer 8 μm map of the dense molecular cloud L183, to examine the importance of scattering as a potential contributor to the line-of-sight extinction.

Results. The column density deduced from the inversion of the 8 μm map, when we neglect scattering, disagrees with all the other column density measurements of the same region. Modeling confirms that scattering at 8 μm is not negligible with an intensity of several hundred kJy sr^-1. This demonstrates the need of efficiently scattering dust grains at mid-infrared wavelengths up to 8 μm. Coagulated aggregates are good candidates and might also explain the discrepancy at high extinction between E(J − K) and τ_9.7 toward dense molecular clouds. Further investigation requires considering efficiently scattering dust grains including ices as realistic dust models.