Wednesday, July 15, 2009 - 3:15pm
Juergen Steinacker (MPIA Heidelberg):
"Direct evidence for dust growth in L183 from MIR cloud shine - A molecular cloud seen in scattered MIR radiation by Spitzer"
Abstract. Theoretical arguments suggest that dust grains should grow in the dense cold parts of molecular clouds. Evidence for larger grains has so far been gathered in Near/Mid Infrared extinction and millimeter observations. Interpreting these data is aggravated due to the complex interplay of density and dust properties, as well as temperature for thermal emission. We present new Spitzer data of L183 which show the cloud in emission in the 3.6 and 4.5 micron band. For 4.5 micron band, no substantial emission from Polycyclic Aromatic Hydrocarbons (PAHs) is expected. Hence, we interpret this emission to be scattered interstellar light ("MIR cloudshine"). The visual extinction AV map derived in a former paper is fitted by a series of 3D Gaussian distribution. For different dust models, we calculate the scattered MIR radiation images of structures being in agreement with the AV map and compare them to the Spitzer data. We find that scattered light modeling assuming interstellar medium dust grains without growth does not reproduce flux measurable by Spitzer. Contrary, models with grains growing with density yield images with a flux and pattern comparable to the Spitzer images in the bands 3.6, 4.5, and 8.0 micron. Further implications of dust grain growth in the inner parts of clouds as well as perspectives to obtain more cloudshine data with upcoming instruments will be discussed.