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تسجيل مستخدم جديدThe VIMOS VLT Deep Survey: Star Formation Rate Density of Lya emitters from a sample of 217 galaxies with spectroscopic redshifts 2<z<6.6
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Aims. The aim of this work is to study the contribution of the Ly-a emitters (LAE) to the star formation rate density (SFRD) of the Universe in the interval 2<z<6.6. Methods. We assembled a sample of 217 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=1.5x10^18 erg/s/cm^2. 133 LAE 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-a, while the remaining 10% could be either [OII]3727 or Ly-a. We computed the LF and derived the SFRD from LAE at these redshifts. Results. The VVDS-LAE sample reaches faint line fluxes F(Lya) = 1.5x1^18 erg/s/cm^2 (corresponding to L(Lya)=10^41 erg/s at z~3) enabling 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=-1.78+0.1-0.12 at z=4, placing on firm statistical grounds trends found in previous LAE studies, and indicating that sub-L* LAE contribute significantly to the SFRD. The projected number density and volume density of faint LAE in 2<z<6.6 with F>1.5x10^18 erg/s/cm^2 are 33 galaxies/arcmin^2 and 4x10^-2 Mpc^-3, respectively. We find that the the observed luminosity function of LAE does not evolve from z=2 to z=6. This implies that, after correction for the redshift-dependent IGM absorption, the intrinsic LF must have evolved significantly over 3 Gyr. The SFRD from LAE contributes to about 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, becoming equivalent to that of Lyman Break galaxies.
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3. We have selected samples of galaxies based solely on their i-band magnitude reaching i_{AB}=24.75. Spectra have been obtained with VIMOS on the ESO-VLT, integrating 0.75h, 4.5h and 18h for the Wide, Deep, and Ultra-Deep nested surveys. A total of 1263 galaxies have been re-observed independently within the VVDS, and from the VIPERS and MASSIV surveys. They are used to establish the redshift measurements reliability, to assess completeness, and to provide a weighting scheme taking into account the survey selection function. We describe the main properties of the VVDS samples, and the VVDS is compared to other spectroscopic surveys. In total we have obtained spectroscopic redshifts for 34594 galaxies, 422 type-I AGN, and 12430 Galactic stars. The survey has enabled to identify galaxies up to very high redshifts with 4669 redshifts in 1<=z_{spec}<=2, 561 in 2<=z_{spec}<=3 and 468 with z_{spec}>3, and specific populations like LAE have been identified out to z=6.62. We show that the VVDS occupies a unique place in the parameter space defined by area, depth, redshift coverage, and number of spectra. The VVDS provides a comprehensive survey of the distant universe, covering all epochs since z, or more than 12 Gyr of cosmic time, with a uniform selection, the largest such sample to date. A wealth of science results derived from the VVDS have shed new light on the evolution of galaxies and AGN, and their distribution in space, over this large cosmic time. A final public release of the complete VVDS spectroscopic redshift sample is available at http://cesam.lam.fr/vvds.
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