2016A&A...585L...4L

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 5µm range and its ability to validate dust properties for dense cores. We want to investigate whether scattering can also play a role at longer wavelengths and to place even tighter constraints on the dust properties. We analyze the inversion of the Spitzer 8µm map of the dense molecular cloud L183, to examine the importance of scattering as a potential contributor to the line-of-sight extinction. The column density deduced from the inversion of the 8µm map, when we neglect scattering, disagrees with all the other column density measurements of the same region. Modeling confirms that scattering at 8µm is not negligible with an intensity of several hundred kJy/sr. This demonstrates the need of efficiently scattering dust grains at mid-infrared wavelengths up to 8µm. 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.