On the dust extinction in high-z galaxies and the case of extremely red objects

We present the preliminary results of Monte Carlo simulations aimed at investigating the effects of realistic dust extinction (absorption + scattering) on the colours of high-z galaxies. In this paper, we concentrate on the case of spheroidal galaxies, and we obtain attenuation curves in the range 0.1-1.2 mu m for different dust spatial distributions, and for a range of values of the dust optical depth, geometrical thickness and inclination of the dust disc. We find that the resultant curves are strongly dependent on the dust geometrical distribution and optical depth. A serendipitous finding is that the strength of the 2200-Angstrom absorption feature depends not only on the optical depth, but also on the dust geometrical distribution. As a first application, we test our results on two high-z galaxies with extremely red colours (HR10 and HR14) in order to infer clues on their ages, dust content and dust spatial distribution. We confirm that HR10 must be a very dusty galaxy, and we suggest that its stellar component should be strongly embedded in the dust in order to reproduce the observed extremely red colours.