2013ApJ...770...27N -
Astrophys. J., 770, 27 (2013/June-2)
Properties of dust grains probed with extinction curves.
NOZAWA T. and FUKUGITA M.
Abstract (from CDS):
Modern data of the extinction curve from the ultraviolet to the near-infrared are revisited to study properties of dust grains in the Milky Way (MW) and the Small Magellanic Cloud (SMC). We confirm that the graphite-silicate mixture of grains yields the observed extinction curve with the simple power-law distribution of the grain size but with a cutoff at some maximal size: the parameters are tightly constrained to be q = 3.5±0.2 for the size distribution a –q and the maximum radius amax= 0.24±0.05 µm, for both MW and SMC. The abundance of grains, and hence the elemental abundance, is constrained from the reddening versus hydrogen column density, E(B - V)/NH. If we take the solar elemental abundance as the standard for the MW, >56% of carbon should be in graphite dust, while it is <40% in the SMC using its available abundance estimate. This disparity and the relative abundance of C to Si explain the difference of the two curves. We find that 50%-60% of carbon may not necessarily be in graphite but in the amorphous or glassy phase. Iron may also be in the metallic phase or up to ∼80% in magnetite rather than in silicates, so that the Mg/Fe ratio in astronomical olivine is arbitrary. With these substitutions, the parameters of the grain size remain unchanged. The mass density of dust grains relative to hydrogen is ρdust/ρH = 1/(120–16+10) for the MW and 1/(760–90+70) for the SMC under the elemental abundance constraints. We underline the importance of the wavelength dependence of the extinction curve in the near-infrared in constructing the dust model: if Aλ∝λ–γ with γ ≃ 1.6, the power-law grain-size model fails, whereas it works if γ ≃ 1.8-2.0.
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Journal keyword(s):
dust, extinction - Galaxy: abundances - ISM: abundances - ISM: general
Simbad objects:
6
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