2001ApJ...552L..17K

We present new results from a systematic study of absorption-line strengths of galaxies in clusters approaching redshifts of unity. In this Letter, we specifically compare the strengths of the high-order Balmer absorption features of Hγ and Hδ in E/S0 galaxies in the four clusters Abell 2256 (z=0.06), Cl 1358+62 (z=0.33), MS 2053-04 (z=0.58), and MS 1054-03 (z=0.83). By comparing the correlation of the Balmer line strengths with the velocity dispersions for E/S0 galaxies in the four clusters, we find moderate evolution in the zero point of the (Hδ_A+Hγ_A)-σ relation with redshift. The trend is consistent with the passive evolution of old stellar populations. Under the assumption that the samples can be compared directly, we use single-burst stellar population synthesis models to constrain the last major occurrences of star formation in the observed E/S0 galaxies to be z_f>2.5 (95% confidence). We have compared the evolution of the Balmer absorption with the evolution of the B-band fundamental plane and find that simple stellar population models agree very well with the data. While the best agreement occurs with a low value for Ω_m, the data provide strong confirmation of the time evolution in recent stellar population models.