摘要：Aims.We compare the far-infrared to sub-millimetre dust emission properties measured in high Galactic latitude cirrus with those determined in a sample of 204 late-type DustPedia galaxies. The aim is to verify if it is appropriate to use Milky Way dust properties to derive dust masses in external galaxies.Methods.We usedHerschelobservations and atomic and molecular gas masses to estimateϵ(250 μm), the disc-averaged dust emissivity at 250μm, and from this, the absorption cross section per H atomσ(250 μm) and per dust massκ(250 μm). The emissivityϵ(250 μm) requires one assumption, which is the CO-to-H2conversion factor, and the dust temperature is additionally required forσ(250 μm); yet another constraint on the dust-to-hydrogen ratio D/H, depending on metallicity, is required forκ(250 μm).Results.We findϵ(250 μm) = 0.82 ± 0.07 MJy sr−1(1020H cm−2)−1for galaxies with 4 < F(250 μm)/F(500 μm) < 5. This depends only weakly on the adopted CO-to-H2conversion factor. The value is almost the same as that for the Milky Way at the same colour ratio. Instead, forF(250 μm)/F(500 μm) > 6,ϵ(250 μm) is lower than predicted by its dependence on the heating conditions. The reduction suggests a variation in dust emission properties for spirals of earlier type, higher metallicity, and with a higher fraction of molecular gas. When the standard emission properties of Galactic cirrus are used for these galaxies, their dust masses might be underestimated by up to a factor of two. Values forσ(250 μm) andκ(250 μm) at the Milky Way metallicity are also close to those of the cirrus. Mild trends of the absorption cross sections with metallicity are found, although the results depend on the assumptions made.
关键词：endustextinctioninfrared: galaxiesgalaxies: photometrygalaxies: ISM
