The Role of the Dust in Primeval Galaxies: A Simple Physical Model for Lyman Break Galaxies and Lyα Emitters

Abstract

We explore the onset of star formation in the early Universe, exploiting the\nobservations of high-redshift Lyman-break galaxies (LBGs) and Lyman alpha\nemitters (LAEs), in the framework of the galaxy formation scenario elaborated\nby Granato et al. (2004) already successfully tested against the wealth of data\non later evolutionary stages. Complementing the model with a simple, physically\nplausible, recipe for the evolution of dust attenuation in metal poor galaxies\nwe reproduce the luminosity functions (LFs) of LBGs and of LAEs at different\nredshifts. This recipe yields a much faster increase with galactic age of\nattenuation in more massive galaxies, endowed with higher star formation rates.\nThese objects have therefore shorter lifetimes in the LAE and LBG phases, and\nare more easily detected in the dusty submillimeter bright phase. The short UV\nbright lifetimes of massive objects strongly mitigate the effect of the fast\nincrease of the massive halo density with decreasing redshift, thus accounting\nfor the weaker evolution of the LBG LF, compared to that of the halo mass\nfunction, and the even weaker evolution between z~6 and z~3 of the LAE LF. LAEs\nare on the average expected to be younger, with lower stellar masses, and\nassociated to less massive halos than LBGs. Finally, we show that the\nintergalactic medium can be completely reionized at redshift z~6-7 by massive\nstars shining in protogalactic spheroids with halo masses from a few 10^10 to a\nfew 10^11 M_sun, showing up as faint LBGs with magnitude in the range\n-17<M_1350<-20, without resorting to any special stellar initial mass function.\n