The Building the Bridge survey for z = 3 Lyα emitting galaxies*
II. Completion of the survey
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark e-mail: firstname.lastname@example.org
2 European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
3 Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 57 avenue d'Azereix, 65000 Tarbes, France
4 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
5 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
6 Institute of Physics and Astronomy, Aarhus University, Ny Munkegade, 8000 Aarhus C, Denmark
Accepted: 26 January 2009
Context. We have substantial information about the kinematics and abundances of galaxies at z ≈ 3 studied in absorption against the light of background QSOs. At the same time we have already studied 1000s of galaxies detected in emission mainly through the Lyman-break selection technique; however, we know very little about how to make the connection between the two data sets.
Aims. We aim at bridging the gap between absorption-selected and emission-selected galaxies at z ≈ 3 by probing the faint end of the luminosity function of star-forming galaxies at z ≈ 3.
Methods. Narrow-band surveys for Lyman-α (Lyα) emitters have proven to be an efficient probe of faint, star-forming galaxies in the high-redshift universe. We performed narrow-band imaging in three fields with intervening QSO absorbers (a damped Lyα absorber and two Lyman-limit systems) using the VLT. We target Lyα at redshifts 2.85, 3.15, and 3.20.
Results. We find a consistent surface density of about 10 Lyα-emitters per square arcmin per unit redshift in all three fields down to our detection limit of about 31041 erg s-1. The luminosity function is consistent with what has been found by other surveys at similar redshifts. About 85% of the sources are fainter than the canonical limit of R = 25.5 for most Lyman-break galaxy surveys. In none of the three fields do we detect the emission counterparts of the QSO absorbers. In particular we do not detect the counterpart of the damped Lyα absorber towards Q2138-4427. This implies that the DLA galaxy is either not a Lyα emitter or is fainter than our flux limit.
Conclusions. Narrow-band surveys for Lyα emitters are excellent for probing the faint end of the luminosity function at z ≈ 3. There is a very high surface density of this class of objects; yet, we only detect galaxies with Lyα in emission, so the density of galaxies with similar broad band magnitudes will be substantially higher. This is consistent with a very steep slope of the faint end of the luminosity function as has been inferred by other studies. This faint population of galaxies is playing a central role in the early Universe. There is evidence that this popualtion is dominating the intergrated star-formation activity, responsible for the bulk of the ionising photons at z ≳ 3 and likely also responsible for the bulk of the enrichment of the intergalactic medium.
Key words: cosmology: observations / galaxies: quasars: individual: BRI 1346 / galaxies: quasars: individual: BRI 1202-0725 / galaxies: quasars: individual: Q 2138-4427 / galaxies: high-redshift
© ESO, 2009