1994A&A...288..103G

In this paper we describe deeper obervations, both imaging and spectroscopy, of the most distant radio-quiet Lyα galaxy known so far, at redshift of z=3.428 (galaxy G2) and of other faint objects in the field around the QSO 0000-2619. Galaxy G2, which we discovered in the field around the damped absorber of the QSO with narrow-band imaging tuned to detect Lyα emission at the redshift of the absorption system, is the best primaeval galaxy candidate identified so far. Here we report measurements of its restframe UV spectral energy distribution in the interval λλ1000, 1700 A, in particular the depression of the continuum due to the blanketing of the intervening Lyα forest and the Lyα emission line, and give better upper limits for the high-ionization emission lines, such as N V and C IV. We conclude that this object is very likely a primaeval galaxy observed during a major episode of star formation and in which dust does not extinguish the Lyα emission. We also present Lyα narrow-band imaging of the galaxy which causes the damped absorber in the spectrum of the QSO. No emission is detected, down to a 3σ upper limit of 1.2x10^–17erg/s/cm² in an aperture of 2 arcsec in diameter. A corresponding upper limit to the rest-frame equivalent width is 6 A. Similar limits apply also to other 13 flat-spectrum z > 3 galaxy candidates identified in the same field by Steidel & Hamilton, if their redshift is such that their Lyα emission falls within our narrow-band filter. However, from their rest-frame UV continuum luminosity, we estimate that the star-formation rates for these galaxies are in the range 30 to 100 M_☉yr^–1. This would suggest that radio-quiet primaeval galaxies, though in a star-forming phase, are not characterized by the intense Lyα emission and large SFRs typical of radio-galaxies. If these candidates are confirmed to be at similar redshifts than those of G2 and the galaxy responsible for the damped system of the QSO, then this association of galaxies would be the most distant cluster observed so far, with a total stellar mass of the order of 10¹³M_☉ (throughout this paper we assume H₀=50km/s/Mpc and {OMEGA}=0, unless differently stated).