A multi-wavelength study of z=3.15 Lyman-α emitters in the GOODS South Field

Context. Ly alpha-emitters have proven to be excellent probes of faint, star-forming galaxies in the high redshift universe. However, although the sample of known emitters is increasingly growing, their nature ( e. g. stellar masses, ages, metallicities, star-formation rates) is still poorly constrained. Aims. We aim to study the nature of Ly alpha-emitters, to find the properties of a typical Ly alpha-emitting galaxy and to compare these properties with the properties of other galaxies at similar redshift, in particular Lyman-break galaxies. Methods. We have performed narrow-band imaging at the VLT, focused on Ly alpha at redshift z approximate to 3.15, in the GOODS-S field. We have identified a sample of Ly alpha-emitting candidates, and we have studied their Spectral Energy Distributions (SEDs). Results. We find that the emitters are best fit by an SED with low metallicity (Z/Z(circle dot) = 0.005), low dust extinction (A(V) approximate to 0.26) and medium stellar masses of approximately 10(9) M-circle dot. The age is not very well constrained. One object out of 24 appears to be a high redshift Ly alpha-emitting dusty starburst galaxy. We find filamentary structure as traced by the Ly alpha-emitters at the 4 sigma level. The rest-frame UV SED of these galaxies is very similar to that of Lyman Break Galaxies (LBGs) and comply with the selection criteria for U-band drop-outs, except they are intrinsically fainter than the current limit for LBGs. Conclusions. Ly alpha-emitters are excellent probes of galaxies in the distant universe, and represent a class of star-forming, dust and AGN free, medium mass objects.