  Attenuation curves in galaxies depend on dust chemical composition, content,
and grain size distribution. Such parameters are related to intrinsic galaxy
properties such as metallicity, star formation rate, and stellar age. Due to
the lack of observational constraints at high redshift, dust empirical curves
measured in the local Universe (e.g. Calzetti and SMC curves) have been
employed to describe the dust attenuation at early epochs. We exploit the high
sensitivity and spectral resolution of the JWST to constrain the dust
attenuation curves in high-z galaxies. Our goals are to check whether dust
attenuation curves evolve with redshift and quantify the dependence of the
inferred galaxy properties on the assumed dust attenuation law. We develop a
modified version of the SED fitting code BAGPIPES by including a detailed dust
attenuation curve parametrization. Dust parameters are derived, along with
galaxy properties, from the fit to the data from FUV to mm bands. Once applied
to three star-forming galaxies at z = 7-8, we find that their attenuation
curves differ from local templates. One out of three galaxies shows a
characteristic MW bump, typically associated to the presence of small
carbonaceous dust grains such as PAHs. This is one of the first evidences
suggesting the presence of PAHs in early galaxies. Galaxy properties such as
stellar mass and SFR inferred from SED fitting are strongly affected by the
assumed attenuation curve, though the adopted star formation history also plays
a major role. Our results highlight the importance of accounting for the
potential diversity of dust attenuation laws when analyzing the properties of
galaxies at the EoR, whose dust properties are still poorly understood. The
application of our method to a larger sample of galaxies observed with JWST can
provide us important insights into the properties of dust and galaxies in the
early universe.
