Astron. Astrophys. 358, L1-L4 (2000)

5. Discussion

Although we have detected a number of Ly emitters in the field of 1138-262, from the present data it is impossible to unambiguously determine whether a significant fraction of these objects form part of the presumed cluster around 1138-262. Note that the observations described here can only detect galaxies with bright Ly emission lines not attenuated by dust and these might comprise merely a small fraction of the galaxy content of the presumed cluster. First, of the whole population of LBGs as studied by S99 only 20% have a Lya rest EW 20 Å. About 50% of the LBGs have the Lya region even in absorption. Second, only a fraction of the cluster galaxies are likely to be actively forming stars. We assume that the ratio of early to late type galaxies in the cluster around 1138-262 is the same as the 1.1:1 ratio in intermediate redshift () clusters as found by Andreon (1998). Taking these two factors into account, the detected Ly galaxies might comprise only 10% of the cluster galaxies present around 1138-262. In addition to this, we miss galaxies emitting Ly outside the limited range of wavelength covered by our narrow band filter. Assuming that the radio galaxy is at rest with respect to the cluster, the wavelength of Ly from galaxies with a positive velocity greater than 860 km s^-1 falls outside the FWHM of the filter. Since present day clusters have velocity dispersions as large as km s^-1 (Mazure et al. 1996), we miss 15% of the velocity range of the presumed cluster around 1138-262 if we assume the same velocity dispersion for clusters at high redshift.

© European Southern Observatory (ESO) 2000

Online publication: June 26, 2000
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