EDP Sciences
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Volume 407, Number 1, August III 2003
Page(s) 147 - 157
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20030840

A&A 407, 147-157 (2003)
DOI: 10.1051/0004-6361:20030840

The Building the Bridge survey for z = 3 Ly $\alpha$ emitting galaxies

I. Method and first results
J. P. U. Fynbo1, 2, 3, C. Ledoux4, P. Møller3, B. Thomsen1 and I. Burud5

1  Department of Physics and Astronomy, University of Århus, Ny Munkegade, 8000 Århus C, Denmark
2  Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
3  European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748, Garching by München, Germany
4  European Southern Observatory, Casilla 19001, Santiago 19, Chile
5  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD21218, USA

(Received 17 March 2003 / Accepted 22 May 2003 )

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 Ly $\alpha$ 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 [ $\ion{O}{ii}$] emitters and one $\ion{C}{iv}$ emitter). The confirmation rate for Ly $\alpha$ 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 Ly $\alpha$ 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 Ly $\alpha$ absorber. This latter fact indicates the existence of a large "pancake"-like structure confirming the earlier suggestions of Francis & Hewitt (1993).

Key words: cosmology: observations -- quasars: individual BRI 1346-0322, Q 2138-4427 -- galaxies: high redshift

Offprint request: J. P. U. Fynbo, jfynbo@phys.au.dk

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© ESO 2003