Abstract

Lyman alpha emitters (LAEs) and Lyman break galaxies (LBGs) represent the most common groups of star-forming galaxies at high z, and the differences between their inherent stellar populations (SPs) are a key factor in understanding early galaxy formation and evolution. We have run a set of SP burst-like models for a sample of 1558 sources at 3.4 < z < 6.8 from the Survey for High-z Absorption Red and Dead Sources (SHARDS) over the GOODS-N field. This work focuses on the differences between the three different observational subfamilies of our sample: LAE-LBGs, no-Ly proportional to LBGs, and pure LAEs. Single and double SP synthetic spectra were used to model the spectral energy distributions, adopting a Bayesian information criterion to analyze under which situations a second SP is required. We find that the sources are well modelled using a single SP in similar to 79 per cent of the cases. The best models suggest that pure LAEs are typically young low-mass galaxies (t similar to 26(-25)(+41) Myr; M-star similar to 5.6(-5.5)(+12.0) x 10(8) M-circle dot), undergoing one of their first bursts of star formation. On the other hand, no-Ly a LBGs require older SPs (t similar to 71 +/- 12 Myr), and they are substantially more massive (M-star similar to 3.5 +/- 1.1 x 10(9) M-circle dot). LAE-LBGs appear as the subgroup that more frequently needs the addition of a second SP, representing an old and massive galaxy caught in a strong recent star-forming episode. The relative number of sources found from each subfamily at each z supports an evolutionary scenario from pure LAEs and single SP LAE-LBGs to more massive LBGs. Stellar mass functions are also derived, finding an increase of M* with cosmic time and a possible steepening of the low-mass slope from z similar to 6 to z similar to 5 with no significant change to z similar to 4. Additionally, we have derived the SFR-M-star relation, finding an SFR proportional to M-star(beta) behaviour with negligible evolution from z similar to 4 to z similar to 6.