ar X iv : a st ro - p h / 97 03 06 2 v 1 1 0 M ar 1 99 7 Galaxies at z ≈ 4 and the Formation of Population II 1

We report the discovery of four high-redshift objects (3.3 < z < 4) observed behind the rich cluster CL0939+4713 (Abell 851). One object (DG 433) has a redshift of z = 3.3453; the other three objects have redshifts of z ≈ 4: A0 at z = 3.9819, DG 353 and P1/P2 at z = 3.9822. It is possible that all four objects are being lensed in some way by the cluster, DG 433 being weakly sheared, A0 being strongly sheared, and DG 353 and P1/P2 being an image pair of a common source object; detailed modelling of the cluster potential will be necessary to confirm this hypothesis. The weakness of common stellar wind features like N V and especially C IV in the spectra of these objects argues for sub-solar metallicities, at least as low as the SMC. DG 353 and DG 433, which have ground-based colors, are moderately dusty [Eint(B − V ) ∼< 0.15], similar to other z > 3 galaxies. Star formation rates range from 2.5 (7.8)h−2 to 22. (78.)h−2 M⊙ yr −1, for q0 = 0.5 (0.05), depending on assumptions about gravitational lensing and extinction, also typical of other z > 3 galaxies. These objects are tenatively identified as the low-metallicity proto-spheroid clumps that will merge to form the Population II components of today’s spheroids. Subject headings: galaxies: formation — galaxies: clusters: individual (CL0939+4713) — gravitational lensing