Dust properties of UV-bright galaxies at z-2.

We investigate the properties of the extinction curve in the rest-frame UV for a sample of 34 UV-luminous galaxies at $2 -0.4$ a significant 2175 A 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 $\langle Z \rangle \sim 0.5 {-} 1$ $Z_{\odot}$, $\langle M_{\rm stars} \rangle \sim 6 \times 10^{10}$ $M_{\odot}$, and $\langle R_{\rm eff} \rangle \sim 4$ 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 $z \sim 2$.