| Abstract
| - Aims. The aim of this work is to study the contribution of the Ly α 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 Ly α 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/cm 2. Of those Ly α emitters, 133 are serendipitous identifications in the 22 arcmin 2 total slit area surveyed with the VVDS-Deep and the 3.3 arcmin 2 from the VVDS Ultra-Deep survey, and 84 are targeted identifications in the 0.62 deg 2 surveyed with the VVDS-DEEP and 0.16 deg 2 from the Ultra-Deep survey. Among the serendipitous targets we estimate that 90% of the emission lines are most probably Ly α, while the remaining 10% could be either [OII]3727 or Ly α. 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(Ly α) = 1.5 × 10 -18 erg/s/cm 2 (corresponding to L(Ly α) ~ 10 41 erg/s at z ~ 3), allows the faint-end slope of the luminosity function to be constrained to α ~ −1.6 ± 0.12 at redshift z ~ 2.5 and to \hbox{$\alpha\sim-1.78^{0.10}_{-0.12}$}α~−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 − α ≲ 10 42.5 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/cm 2 are 33 galaxies/arcmin 2 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.
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