Ly α emission galaxies at a redshift of z ≈ 5 . 7 in the FORS Deep Field ⋆

We present the results of a search for Lyα emission galaxies at z ≈ 5.7 in the FORS Deep Field. The objective of this study is to improve the faint end of the luminosity function of high-redshift Lyα emitting galaxies and to derive properties of intrinsically faint Lyα emission galaxies in the young universe. Using FORS2 at the ESO VLT and a set of special interference filters, we identified candidates for high-redshift Lyα galaxies. We then used FORS2 in spectroscopic mode to verify the identifications and to study their spectral properties. The narrow-band photometry resulted in the detection of 15 likely Lyα emission galaxies. Spectra with an adequate exposure time could be obtained for eight galaxies . In all these cases the presence of Lyα emission at z = 5.7 was confirmed spectroscopically. The line fluxes of the 15 candidates range between 3 × 10Wm and 16 × 10Wm, which corresponds to star-formation rates not corrected for dust between 1 and 5 M⊙yr . The luminosity function derived for our photometrically identified objects extends the published luminosity functions of intrinsically brighter Lyα galaxies. With this technique the study of high-redshift Lyα emission galaxies can be extended to low intrinsic luminosities.