Astronomy and Astrophysics, volume 497, 689-702 (2009/4-3)
The building the bridge survey for z = 3 Lyα emitting galaxies. II. Completion of the survey.
GROVE L.F., FYNBO J.P.U., LEDOUX C., LIMOUSIN M., MOLLER P., NILSSON K.K. and THOMSEN B.
Abstract (from CDS):
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. 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. 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. 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 3x1041erg/s. 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 z=2.85 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. 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.
cosmology: observations - galaxies: quasars: individual: BRI1346 - galaxies: quasars: individual: BRI1202-0725 - galaxies: quasars: individual: Q2138-4427 - galaxies: high-redshift
Tables A.1, A.4: LEGO 1202-NN (Nos 1-25). Tables A.2, A.4: LEGO 1346-NN N=24 among (Nos 1-26). Tables A.3, A.4: LEGO 2138-NN N=34 among (Nos 1-35).
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