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Direct evidence of dust growth in L183 from mid-infrared light scattering

Steinacker, J. and Pagani, L. and Bacmann, A. and Guieu, S. (2010) Direct evidence of dust growth in L183 from mid-infrared light scattering. Astronomy and Astrophysics, 511 . A9. ISSN 0004-6361.

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Context. Theoretical arguments suggest that dust grains should grow in the dense cold parts of molecular clouds. Evidence of larger grains has so far been gathered in near/mid infrared extinction and millimeter observations. Interpreting the data is, however, aggravated by the complex interplay of density and dust properties (as well as temperature for thermal emission). Aims. Direct evidence of larger particles can be derived from scattered mid-infrared (MIR) radiation from a molecular cloud observed in a spectral range where little or no emission from polycyclic aromatic hydrocarbons (PAHs) is expected. Methods. We present new Spitzer data of L183 in bands that are sensitive and insensitive to PAHs. The visual extinction AV map derived in a former paper was fitted by a series of 3D Gaussian distributions. For different dust models, we calculate the scattered MIR radiation images of structures that agree with the AV map and compare them to the Spitzer data. Results. The Spitzer data of L183 show emission in the 3.6 and 4.5 μm bands, while the 5.8 μm band shows slight absorption. The emission layer of stochastically heated particles should coincide with the layer of strongest scattering of optical interstellar radiation, which is seen as an outer surface on I band images different from the emission region seen in the Spitzer images. Moreover, PAH emission is expected to strongly increase from 4.5 to 5.8 μm, which is not seen. Hence, we interpret this emission to be MIR scattered light from grains located further inside the core, and call it ”coreshine”. Scattered light modeling when assuming interstellar medium dust grains without growth does not reproduce flux measurable by Spitzer. In contrast, 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 μm. Conclusions. There is direct evidence of dust grain growth in the inner part of L183 from the scattered light MIR images seen by Spitzer.

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Additional Information: © ESO 2010. Received: 6 July 2009; accepted: 30 November 2009. This research has made use of NASA’s Astrophysics Data System Abstract Service. We are thankful to François Ménard, Nikolai Voshchinnikov, Thomas Henning, Cornelius Dullemond, and Roy van Boeckel for fruitful discussions and to Nicolas Flagey for his help with Spitzer data.
Subject Keywords:dust, extinction; ISM: clouds; ISM: individual objects: L183; infrared: ISM; radiative transfer; scattering
Record Number:CaltechAUTHORS:20100413-105938157
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Official Citation:Direct evidence of dust growth in L183 from mid-infrared light scattering J. Steinacker, L. Pagani, A. Bacmann and S. Guieu A&A 511 A9 (2010) DOI: 10.1051/0004-6361/200912835
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17959
Deposited By: Jason Perez
Deposited On:13 Apr 2010 20:21
Last Modified:03 Oct 2019 01:36

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