Geometry Effects On Dust Attenuation Curves With Different Grain Sources At High Redshift

Dust has been detected in high-redshift (z > 5) galaxies but its origin is still being debated. Dust production in high-redshift galaxies could be dominated by stellar production or by accretion (dust growth) in the interstellar medium. Previous studies have shown that these two dust sources predict different grain-size distributions, which lead to significantly different extinction curves. In this paper, by performing radiative transfer calculations, we investigate how the difference in the extinction curves affects the dust attenuation properties of galaxies. To examine the major effects of the dust-stars distribution geometry, we adopt two representative cases in spherical symmetry: the well-mixed geometry (stars and dust are homogeneously mixed) and the two-layer geometry (young stars are more concentrated in the centre). In both cases, we confirm that the attenuation curve can be drastically steepened by scattering and by different optical depths between young and old stellar populations, and can be flattened by the existence of unobscured stellar populations. We can reproduce similar attenuation curves even with very different extinction curves. Thus, we conclude that it is difficult to distinguish dust sources only with attenuation curves. However, if we include information on dust emission and plot the relation between infrared excess (IRX) and the ultraviolet spectral slope (beta), then different dust sources predict different positions in the IRX-beta diagram. A larger beta is preferred under a similar IRX if dust growth is the dominant dust source.