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

Aims: The aim of this work is to study the contribution of the Lyalpha 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 Lyalpha 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 Lyalpha emitters, 133 are serendipitous identifications in the 22 arcmin2 total 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 Lyalpha, while the remaining 10% could be either [OII]3727 or Lyalpha. 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(Lyalpha) = 1.5 × 10-18 erg/s/cm2 (corresponding to L(Lyalpha) ~ 1041 erg/s at z ~ 3), allows the faint-end slope of the luminosity function to be constrained to alpha ~ -1.6 ± 0.12 at redshift z ~ 2.5 and to alpha ~ -1.78-0.120.10 at redshift ~4, placing trends found in previous LAE studies on firm statistical grounds, and indicating that sub-L_* LAE (LLy-alpha ⪅ 1042.5 erg/s) contribute significantly to the SFRD. The projected number density and volume density of faint LAE in 2 <= z <= 6.6 with F > 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.