2019A&A...631A.102B

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 used Herschel observations and atomic and molecular gas masses to estimate ε(250µm), the disc-averaged dust emissivity at 250µm, and from this, the absorption cross section per H atom σ(250µm) and per dust mass κ(250µm). The emissivity ε(250µm) requires one assumption, which is the CO-to-H₂ conversion factor, and the dust temperature is additionally required for σ(250µm); yet another constraint on the dust-to-hydrogen ratio D/H, depending on metallicity, is required for κ(250µm).
Results. We find ε(250µm)=0.82±0.07MJy/sr/(10²⁰H/cm²) for galaxies with 4<F(250µm)/F(500µm)<5. This depends only weakly on the adopted CO-to-H₂ conversion factor. The value is almost the same as that for the Milky Way at the same colour ratio. Instead, for F(250µm)/F(500µm)>6, ε(250µm) 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 for σ(250µm) and κ(250µm) 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.