4. Colour of the deflector
The redshift of the lensing galaxy can be constrained by the colour. In Fig. 4, we compare the colour of the candidate (the shaded region) with theoretical colours corresponding to five galaxy types. These colours were obtained from the PEGASE "Projet d'Etude des GAlaxies par Synthèse Evolutive" atlas (Leitherer et al. 1996; Fioc and Rocca-Volmerange 1997). The five types correspond to E, Sa, Sb, Sc and Sd galaxies in a critical density universe with (Rocca-Volmerange and Fioc 1996). The theoretical colours are a function of redshift. The thick lines include the effect of galaxy evolution; the thin lines do not.
The colour of the candidate constrains the object to be a galaxy with a redshift beyond , probably between z=1 and z=2. The redshifts of the two strongest metal absorption line systems, at and (Smette et al. 1995 and Wisotzki et al. 1993) are marked with dotted arrows in Fig. 4.
Without a firm redshift for the lens, its absolute magnitude is unknown. However, if the galaxy is between and (as also suggested by Smette et al. 1995) it is many times more luminous than a typical large galaxy, which would have . This value we adopted for is the average between the value determined by Glazebrook et al. (1995) and the one from Mobasher et al. (1993).
© European Southern Observatory (ESO) 1998
Online publication: January 8, 1998