Dust evolution across the Horsehead nebula

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http://hdl.handle.net/10138/318650

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Schirmer , T , Abergel , A , Verstraete , L , Ysard , N , Juvela , M , Jones , A P & Habart , E 2020 , ' Dust evolution across the Horsehead nebula ' , Astronomy & Astrophysics , vol. 639 , 144 . https://doi.org/10.1051/0004-6361/202037937

Title: Dust evolution across the Horsehead nebula
Author: Schirmer, T.; Abergel, A.; Verstraete, L.; Ysard, N.; Juvela, M.; Jones, A. P.; Habart, E.
Contributor: University of Helsinki, Department of Physics
Date: 2020-07-23
Language: eng
Number of pages: 16
Belongs to series: Astronomy & Astrophysics
ISSN: 0004-6361
URI: http://hdl.handle.net/10138/318650
Abstract: Context. Micro-physical processes on interstellar dust surfaces are tightly connected to dust properties (i.e. dust composition, size, and shape) and play a key role in numerous phenomena in the interstellar medium (ISM). The large disparity in physical conditions (i.e. density and gas temperature) in the ISM triggers an evolution of dust properties. The analysis of how dust evolves with the physical conditions is a stepping stone towards a more thorough understanding of interstellar dust.Aims. We highlight dust evolution in the Horsehead nebula photon-dominated region.Methods. We used Spitzer/IRAC (3.6, 4.5, 5.8 and 8 mu m) and Spitzer/MIPS (24 mu m) together with Herschel/PACS (70 and 160 mu m) and Herschel/SPIRE (250, 350 and 500 mu m) to map the spatial distribution of dust in the Horsehead nebula over the entire emission spectral range. We modelled dust emission and scattering using the THEMIS interstellar dust model together with the 3D radiative transfer code SOC.Results. We find that the nano-grain dust-to-gas ratio in the irradiated outer part of the Horsehead is 6-10 times lower than in the diffuse ISM. The minimum size of these grains is 2-2.25 times larger than in the diffuse ISM, and the power-law exponent of their size distribution is 1.1-1.4 times lower than in the diffuse ISM. In the denser part of the Horsehead nebula, it is necessary to use evolved grains (i.e. aggregates, with or without an ice mantle).Conclusions. It is not possible to explain the observations using grains from the diffuse medium. We therefore propose the following scenario to explain our results. In the outer part of the Horsehead nebula, all the nano-grain have not yet had time to re-form completely through photo-fragmentation of aggregates and the smallest of the nano-grain that are sensitive to the radiation field are photo-destroyed. In the inner part of the Horsehead nebula, grains most likely consist of multi-compositional mantled aggregates.
Subject: ISM: individual objects: Horsehead nebula
photon-dominated region
dust
extinction
evolution
MULTIBAND IMAGING PHOTOMETER
INTERSTELLAR DUST
PHOTODISSOCIATION REGIONS
ABSOLUTE CALIBRATION
SIZE DISTRIBUTION
STAR-FORMATION
COLD DUST
EXTINCTION
EMISSION
SPITZER
115 Astronomy, Space science
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