On the Age Estimation of LBDS 53W091

The recent spectral analysis of LBDS 53W091 by Spinrad and his collaboratorshas suggested that this red galaxy at z=1.55 is at least 3.5 Gyr old. Thisimposes an important constraint on cosmology, suggesting that this galaxyformed at z > 6.5, assuming recent estimates of cosmological parameters. Wehave performed chi^2 tests to the continuum of this galaxy using its UVspectrum and photometric data (RJHK). We have used the updated Yi models thatare based on the Yale tracks. We find it extremely difficult to reproduce suchlarge age estimates, under the assumption of the most probable inputparameters. Using the same configuration as in Spinrad et al. (solar abundancemodels), our analysis suggests an age of approximately 1.4 -- 1.8 Gyr. Thediscrepancy between Spinrad et al.'s age estimate (based on the 1997 Jimenezmodels) and ours originates from the large difference in the model integratedspectrum: the Jimenez models are much bluer than the Yi models and the Bruzual\& Charlot (BC) models. Preliminary tests favor the Yi and BC models. Theupdated age estimate of LBDS 53W091 would suggest that this galaxy formedapproximately at z=2-3.Comment: LaTeX, 18 eps files Accepted for publication in ApJ (Feb 10, 2000, vol 530), uses emulateapj.st