摘要：The fraction of Lyman-αemitters (LAEs) among the galaxy population has been found to increase fromz~ 0toz~ 6and drop dramatically atz> 6. This drop has been interpreted as an effect of an increasingly neutral intergalactic medium (IGM) with increasing redshift, while a Lyman continuum escape fraction evolving with redshift and/or a sudden change of galaxy physical properties can also contribute to the decreasing LAE fraction. We report the result of a large VLT/FORS2 program aiming to confirm spectroscopically a large galaxy sample atz≥ 6that has been selected in several independent fields through the Lyman break technique. Combining those data with archival data, we create a large and homogeneous sample ofz~ 6galaxies (N= 127), complete in terms of Lyαdetection at> 95%for Lyαequivalent widthEW(Lyα) ≥ 25 Å. We use this sample to derive a new measurement of the LAE fraction atz~ 6and derive the physical properties of these galaxies through spectral energy distribution (SED) fitting. We find a median LAE fraction atz~ 6lower than in previous studies, while our sample exhibits typical properties forz~ 6galaxies in terms ofUVluminosity andUVβslope. The comparison of galaxy physical properties between LAEs and non-LAEs is comparable to results at lower redshift: LAEs with the largest EW(Lyα) exhibit bluerUVslopes, are slightly less massive and less star-forming. The main difference between LAEs and non-LAEs is that the latter are significantly dustier. Using predictions of our SED fitting code accounting for nebular emission, we find an effective Lyαescape fractionfesceff(Lyα) = 0.23-0.17+0.36remarkably consistent with the value derived by comparingUVluminosity function with Lyαluminosity function. We conclude that the drop in the LAE fraction fromz~ 6toz> 6is less dramatic than previously found and the effect of an increasing IGM neutral fraction is possibly observed at5
关键词：engalaxies: high-redshiftgalaxies: evolutiondark ages, reionization, first stars
