Abstract. We present the first results of an observational programme at the ESO Very Large Telescope aimed at detecting a large sample of high-redshift galaxies fainter than the current spectroscopic limit of R = 25.5 for Lyman-Break galaxies. In this paper, we describe the results of deep narrow and broad-band imaging and subsequent follow-up multi-object spectroscopy of faint high-redshift galaxies in the fields of the QSOs BRI 1346−0322 and Q 2138−4427. These QSOs have intervening high neutral hydrogen column density absorbers, at redshifts z = 2.85 and z = 3.15 respectively, for which redshifted Lyα emission falls within less than a few Å from the central wavelengths of existing VLT (∼60 Å-wide) narrow-band filters. We selected 37 and 27 candidate emission-line galaxies in the two fields respectively. Most (∼85%) of the candidates have R-band magnitudes fainter than R = 25.5. The first spectroscopic follow-up of a sub-sample of the candidates resulted in 41 confirmed candidates and 4 foreground emission line galaxies (three [O ] emitters and one C  emitter). The confirmation rate for Lyα emitters is 82% and 68% in the field of BRI 1346−0322 and Q 2138−4427 respectively. In addition, we serendipitously detect a number of other emission-line sources on some of the slitlets not used for candidates. Of these, 9 are also most likely Lyα emitters with redshifts ranging from 1.98 to 3.47. The redshift distribution of confirmed candidates in the field of BRI 1346−0322 is consistent with being drawn from a uniform distribution weighted by the filter response curve, whereas the galaxies in the field of Q 2138−4427 have redshifts clustering very close to the redshift of the damped Lyα absorber. This latter fact indicates the existence of a large "pancake"-like structure confirming the earlier suggestions of Francis & Hewitt (1993).

Abstract. We present Ulysses and NEAR data from the detection of the short or intermediate duration (2 s) gamma-ray burst GRB 000301C (2000 March 1.41 UT). The gamma-ray burst (GRB) was localised by the Inter Planetary Network (IPN) and RXTE to an area of ∼50 arcmin 2 . A fading optical counterpart was subsequently discovered with the Nordic Optical Telescope (NOT) about 42 h after the burst. The GRB lies at the border between the long-soft and the short-hard classes of GRBs. If GRB 000301C belongs to the latter class, this would be the first detection of an afterglow to a short-hard burst. We present UBRI photometry from the time of the discovery until 11 days after the burst. We also present JHK photometry obtained with UKIRT on 2000 March 4.5 UT (3.1 days after the burst). Finally, we present spectroscopic observations of the optical afterglow obtained with the ESO VLT Antu telescope 4 and 5 days after the burst. The optical light curve is consistent with being achromatic from 2 to 11 days after the burst and exhibits a break. A broken power-law fit yields a shallow pre-break decay power-law slope of α1 = −0.72 ± 0.06, a break time of t break = 4.39 ± 0.26 days after the burst, and a post-break slope of α2 = −2.29 ± 0.17. These properties of the light curve are best explained by a sideways expanding jet in an ambient medium of constant mean density. In the optical spectrum we find absorption features that are consistent with Fe ii, C iv, C ii, Si ii and Lyα at a redshift of 2.0404 ± 0.0008. We find evidence for a curved shape of the spectral energy distribution of the observed afterglow. It is best fitted with a power-law spectral distribution with index β ∼ −0.7 reddened by an SMC-like extinction law with AV ∼ 0.1 mag. Based on the Lyα absorption line we estimate the H i column density to be log(N(H i)) = 21.2 ± 0.5. This is the first direct indication of a connection between GRB host galaxies and Damped Lyα Absorbers.

Abstract. We present spectroscopic observations obtained with the ESO Very Large Telecope (VLT) of seven candidate Lyα emitting galaxies in the field of the radio quiet Q1205-30 at z = 3.04 previously detected with deep narrow band imaging. Based on equivalent widths and limits on line ratios we confirm that all seven objects are Lyα emitting galaxies. Deep images also obtained with the VLT in the B and I bands show that five of the seven galaxies have very faint continuum fluxes (I(AB) ≈ 26.8 and B(AB) ≈ 27.3). The star formation rates of these seven galaxies estimated from the rest-frame UV continuum around 2000Å, as probed by the I-band detections, as well as from the Lyα luminosities, are 1-4 M yr −1 assuming a Hubble constant of 65 km s −1 Mpc −1 , Ωm = 0.3, and ΩΛ = 0.7. This is 1-3 orders of magnitude lower than for other known populations of star-forming galaxies at similar redshifts (the Lyman-Break galaxies and the sub-mm selected sources). The inferred density of the objects is high, 16 ± 4 per arcmin 2 per unit redshift. This is consistent with the integrated luminosity function for Lyman-Break galaxies down to R = 27 if the fraction of Lyα emitting galaxies is ≈70% at the faint end of the luminosity function. However, if this fraction is 20% as reported for the bright end of the luminosity function then the space density in this field is significantly larger (by a factor of 3.5) than expected from the luminosity function for Lyman-Break galaxies in the HDF-North. This would be an indication that at least some radio quiet QSOs at high redshift reside in overdense environments or that the faint end slope of the high redshift luminosity function has been underestimated. We find evidence that the faint Lyα galaxies are essentially dust-free. These observations show that Lyα emission is an efficient method by which to probe the faint end of the luminosity function at high redshifts.

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Abstract. We report on the results of deep narrow-band Lyα and broad-band U and I imaging of the fields of two Gamma-Ray bursts at redshift z = 2.04 (GRB 000301C and GRB 000926). We find that the host galaxy of GRB 000926 is an extended (more than 2 arcsec), strong Lyα emitter with a rest-frame equivalent width of 71 +20 −15Å . The galaxy consists of two main components and several fainter knots. GRB 000926 occurred in the western component, whereas most of the Lyα luminosity (about 65%) originates in the eastern component. Using archival HST images of the host galaxy we measure the spectral slopes (f λ ∝ λ β ) of the two components to β = −2.4 ± 0.3 (east) and −1.4 ± 0.2 (west). This implies that both components contain at most small amounts of dust, consistent with the observed strong Lyα emission. The western component has a slightly redder V − I colour than the eastern component, suggesting the presence of at least some dust. We do not detect the host galaxy of GRB 000301C in neither Lyα emission nor in U and I broad-band images. The strongest limit comes from combining the narrow and U -band imaging where we infer a limit of U (AB) > 27.7 (2σ limit per arcsec 2 ). The upper limits on the Lyα flux implies a Lyα equivalent width upper limit of ∼150Å. We find eleven and eight other galaxies with excess emission in the narrow filter in the fields of GRB 000301C and GRB 000926 respectively. These galaxies are candidate Lyα emitting galaxies in the environment of the host galaxies. Based on these detections we conclude that GRB 000926 occurred in one of the strongest centres of star formation within several Mpc, whereas GRB 000301C occurred in an intrinsically very faint galaxy far from being the strongest centre of star formation in its galactic environment. Under the hypothesis that GRBs trace star formation, the wide range of GRB host galaxy luminosities implies a very steep faint end slope of the high redshift galaxy luminosity function.