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 toinvestigate the effects of realistic dust extinction (absorption + scattering)on the colours of high-z galaxies. In this paper, we concentrate on the case ofspheroidal galaxies, and we obtain attenuation curves in the range0.1-1.2$\mu$m for different dust spatial distributions, and for a range ofvalues of the dust optical depth, geometrical thickness and inclination of thedust disk. We find that the resultant curves are strongly dependent on the dustgeometrical distribution and optical depth. A serendipitous finding is that thestrength of the 2200 \AA absorption feature depends not only on the opticaldepth, 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 andHR14) in order to infer clues on their ages, dust content and dust spatialdistribution. We confirm that HR10 must be a very dusty galaxy, and we suggestthat its stellar component should be strongly embedded in the dust in order toreproduce the observed extremely red colours.Comment: 7 pages, MNRAS LaTeX, 3 figure