  Dust attenuation shapes the spectral energy distribution of galaxies. It is
particularly true for dusty galaxies in which stars experience a heavy
attenuation. The combination of UV-to-IR photometry with the spectroscopic
measurement of the H$\alpha$ recombination line helps to quantify dust
attenuation of the whole stellar population and its wavelength dependence. We
selected an IR complete sample of galaxies in the COSMOS 3D-HST CANDELS field
detected with the Herschel satellite with a signal to noise ratio larger than
five. Optical to NIR photometry is available as well as NIR spectroscopy for
each source. We reduced the sample to the redshift range $0.6 < z < 1.6$ to
include the H$\alpha$ line in the G141 grism spectra. We have used a new
version of the CIGALE code to fit simultaneously the continuum and H$\alpha$
line emission of the 34 selected galaxies. Using flexible attenuation laws with
free parameters, we are able to measure the shape of the attenuation curve for
each galaxy as well as the amount of attenuation of each stellar population,
the former being in general steeper than the starburst law in the UV-optical
with a large variation of the slope among galaxies. The attenuation of young
stars or nebular continuum is found on average about twice the attenuation
affecting older stars, again with a large variation. Our model with power-laws,
based on a modification of the Charlot and Fall recipe, gives results in better
agreement with the radiative transfer models than the global modification of
the slope of the Calzetti law.
