We present the spectroscopic confirmation of a $z=2.45$ proto-cluster. Its member galaxies lie within a radius of 1.4Mpc (physical) on the sky and within $Delta v pm 700$km/s along the line of sight. We estimate an overdensity of 10, suggesting that
the structure has made the turn-around but is not assembled yet. Comparison to the Millennium simulation suggests that analogous structures evolve into $10^{14}-10^{15}$M$_{odot}$/h type dark matter haloes by $z=0$ qualifying the notion of proto-cluster. The search for the complete census of mock progenitor galaxies at $zsim2.5$ of these massive $z=0$ mock clusters reveals that they are widely spread over areas with a diameter of 3-20Mpc. This suggests that the optical selection of such proto-clusters can result in a rich diversity regarding their $z=0$ descendants. We also searched for signs of environmental differentiation in this proto-cluster. Whilst we see a weak trend for more massive and more quiescent galaxies in the proto-cluster, this is not statistically significant.
[Abridged]. Here, we report on the discovery of the galaxy counterpart of the z_abs=2.58 DLA on the line-of-sight to the z=3.07 quasar SDSS J091826.16+163609.0. The galaxy counterpart of the DLA is detected in the OIII 5007 and OII 3726,3729 emission
lines redshifted into the NIR at an impact parameter of 16 kpc. Ly-alpha emission is not detected. The upper limit implies that Ly-alpha emission from this galaxy is suppressed by more than an order of magnitude. The DLA is amongst the most metal-rich DLAs studied so far at comparable redshifts. We find evidence for substantial depletion of refractory elements onto dust grains. Fitting the main metal line component of the DLA, which is located at z_abs=2.5832 and accounts for at least 85% of the total column density of low-ionisation species, we measure metal abundances from ZnII, SII, SiII, CrII, MnII, FeII and NiII of -0.12, -0.26, -0.46, -0.88, -0.92, -1.03 and -0.78, respectively. In addition, we detect absorption in the Lyman and Werner bands of hydrogen, which represents the first detection of H_2 molecules with X-shooter. The background quasar Q0918+1636 is amongst the reddest QSOs at redshifts 3.02<z<3.12 from the SDSS catalogue. Its UV to NIR spectrum is well fitted by a composite QSO spectrum reddened by SMC/LMC-like extinction curves at z_abs=2.58 with a significant amount of extinction given by A_V = 0.2 mag. This supports previous claims that there may be more metal-rich DLAs missing from current samples due to dust reddening of the background QSOs. The fact that there is evidence for dust both in the central emitting regions of the galaxy (as evidenced by the lack of Ly-alpha emission) and at an impact parameter of 16 kpc (as probed by the DLA) suggests that dust is widespread in this system.
(Abridged). 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. We have performed narrow-band imaging in three fields with i
ntervening QSO absorbers (a damped Ly$alpha$ absorber and two Lyman-limit systems) using the VLT. We target Ly-alpha at redshifts 2.85, 3.15 and 3.20. We find a consistent surface density of about 10 Ly-alpha-emitters per square arcmin per unit redshift in all three fields down to our detection limit of about 3x10^41 ergs 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 z=2.85 damped Ly-alpha absorber towards Q2138-4427. Narrow-band surveys for Ly-alpha emitters are excellent to probe the faint end of the luminosity function at z~3. There is a very high surface density of this class of objects. 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 population is dominating the integrated star-formation activity, responsible for the bulk of the ionizing photons at z~3 and likely also responsible for the bulk of the enrichment of the intergalactic medium.
