(B-I) vs (I-K)

The left panel shows the (B-I) vs (I-K) color of the K < 20 sample from Songaila et al. 1995 (Ap. J. Suppl. 94, 461); the right panel shows this for the K = 2 0-21.75 sample in the HDF. The lines show the expected color tracks for unevolved ellipticals (top), Sbs (middle) and Im (bottom) for redshifts from 0 to 2. With the precise optical data we can see that the faint K counts are entirely dominated by extremely blue galaxies and that there is only a handful of objects that can have the color of even an Sb, much beyond z = 1. Here I is Kron Cousins and B and K are Johnson.