We investigate the properties of the extinction curve in the rest-frame UV for a sample of 34 UV-luminous galaxies at 2 < z < 2.5 , selected from the FORS Deep Field ( FDF ) spectroscopic survey .
A new parametric description of the rest-frame UV spectral energy distribution is adopted ; its sensitivity to properties of the stellar populations or of dust attenuation is established with the use of models .
The latter are computed by combining composite stellar population models and calculations of radiative transfer of the stellar and scattered radiation through the dusty interstellar medium ( ISM ) for a dust/stars configuration describing dust attenuation in local starbursts .
In the favoured configuration the stars are enveloped by a shell with a two-phase , clumpy , dusty ISM .
The distribution of the z \sim 2 UV-luminous FDF galaxies in several diagnostic diagrams shows that their extinction curves range between those typical of the Small and Large Magellanic Clouds ( SMC and LMC , respectively ) .
For the majority of strongly reddened objects having a UV continuum slope \beta > -0.4 a significant 2175 Å absorption feature ( or “ UV bump ” ) is inferred , indicating an LMC-like extinction curve .
On the other hand , the UV continua of the least reddened objects are mostly consistent with SMC-like extinction curves , lacking a significant UV bump , as for the sample of local starbursts investigated by Calzetti and collaborators .
Furthermore , the most opaque ( \beta \sim 0 ) and , thus ( for our models ) , dustiest UV-luminous FDF galaxies tend to be among the most metal rich , most massive , and largest systems at z \sim 2 , indicating \langle Z \rangle \sim 0.5 - 1 Z _ { \odot } , \langle M _ { stars } \rangle \sim 6 \times 10 ^ { 10 } M _ { \odot } , and \langle R _ { eff } \rangle \sim 4 kpc , respectively .
The presence of the UV bump does not seem to depend on the total metallicity , as given by the equivalent width ( EW ) of the C IV doublet .
Conversely , it seems to be associated with a large average EW of the six most prominent interstellar low-ionisation absorption lines falling in the FORS spectra .
The average EW of these saturated lines offers a proxy for the ISM topology .
We interpret these results as the evidence for a difference in the properties of the dusty ISM among the most evolved UV-luminous , massive galaxies at z \sim 2 .