  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, we investigate how the difference
in the extinction curves affects the dust attenuation properties of galaxies by
performing radiative transfer calculations. 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 the dust sources only with attenuation curves.
However, if we include information on dust emission and plot the IRX (infrared
excess)--$\beta$ (ultraviolet spectral slope) relation, 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.

Astrophysics of Galaxies