The VIMOS VLT Deep Survey: Star formation rate density of Lyα emitters from a sample of 217 galaxies with spectroscopic redshifts 2≤z≤6.6

Abstract

Aims. The aim of this work is to study the contribution of the Lya emitters to the star formation rate density (SFRD) of the Universe in the interval 2 < z < 6.6. Methods. We assembled a sample of 217 Lya emitters (LAE) from the Vimos-VLT Deep Survey (VVDS) with secure spectroscopic redshifts in the redshift range 2 < z < 6.62 and fluxes down to F ∼ 1.5 × 10 -18 erg/s/cm2. Of those LLy-α emitters, 133 are serendipitous identifications in the 22 arcmin2total slit area surveyed with the VVDS-Deep and the 3.3 arcmin2 from the VVDS Ultra-Deep survey, and 84 are targeted identifications in the 0.62 deg2 surveyed with the VVDS-DEEP and 0.16 deg2 from the Ultra-Deep survey. Among the serendipitous targets we estimate that 90% of the emission lines are most probably Lya, while the remaining 10% could be either [OII]3727 or L Ly-αa. We computed the luminosity function (LF) and derived the star-formation rate density using this sample of LAE. Results. The VVDS-LAE sample reaches faint line fluxes F(Lya) = 1.5 × 10-18 erg/s/cm2 (corresponding to L(LLy-α) ∼ 1041 erg/s at z ∼ 3), allows the faint-end slope of the luminosity function to be constrained to a ∼ -1.6 ± 0.12 at redshift z ∼ 2.5 and to a ∼ -1.780.10 -0.12 at redshift ∼4, placing trends found in previous LAE studies on firm statistical grounds, and indicating that sub-L*LAE (L Ly-a 1.5 × 10-18 erg/s/cm2 are 33 galaxies/arcmin2 and ∼4 × 10-2 Mpc-3, respectively. We find that the observed luminosity function (LF) of LAEs does not evolve from z = 2 to z = 6. This implies that, after correction for the redshift-dependent IGM absorption, the intrinsic luminosity function must have evolved significantly over 3 Gyr. The SFRD from LAE contributes around 20% of the SFRD at z = 2-3, while the LAE appear to be the dominant source of star formation producing ionizing photons in the early universe z ∼> 5-6, equivalent to Lyman Break galaxies. © 2010 ESO.