Keck Spectroscopy of Redshiftz∼ 3 Galaxies in the Hubble Deep Field

Abstract

We have obtained spectra with the 10-m Keck telescope of a sample of 24 galaxies having colors consistent with star-forming galaxies at redshifts 2 < ∼ z < ∼ 4.5 in the Hubble Deep Field (HDF). Eleven of these galaxies are confirmed to be at high redshift (z med = 3.0), one is at z = 0.5, and the other 12 have uncertain redshifts but have spectra consistent with their being at z > 2. The spectra of the confirmed high-redshift galaxies show a diversity of features, including weak Lyα emission, strong Lyα breaks or damped Lyα absorption profiles, and the stellar and interstellar rest-UV absorption lines common to local starburst galaxies and high-redshift star-forming galaxies reported recently by others. The narrow profiles and low equivalent widths of C IV, Si IV, and N V absorption lines may imply low stellar metallicities. Combined with the 5 high-redshift galaxies in the HDF previously confirmed with Keck spectra by Steidel et al. (1996b), the 16 confirmed sources yield a comoving volume density of n ≥ 2.5 × 10 −4 h 3 50 Mpc −3 for q 0 = 0.05, or n ≥ 1.2 × 10 −3 h 3 50 Mpc −3 for q 0 = 0.5. These densities are 3 − 4 times higher than the recent estimates of 1 Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the

The z=2.72 galaxy cB58: a gravitational fold arc lensed by the cluster MS 1512+36

“…Thus the unlensed source A agrees in R-magnitude, redshift and half light radius with the galaxy C2-05 in the HDF (Steidel et al 1996b). To compare with absolute B-band luminosity of other high redshift galaxies (Lowenthal et al 1997, Fig. 6) we avoid the uncertainties related to the kV correction and simply consider the H band which is approximately equivalent to the rest B band at z=2.72.…”

“…If one shifts the data point for cB58 in the magnitude-redshift plane in Fig. 5 of Lowenthal et al (1997) by that amount, one sees that the source of cB58 is a normal 'z = 3-Steidel galaxy' in the I-magnitude -redshift plane. This is also valid for the source size: the half-light radius of A2 is 0.…”

Hubble Space TelescopeImaging and Keck Spectroscopy ofz≈ 6i‐Band Dropout Galaxies in the Advanced Camera for Surveys GOODS Fields

“…Lowenthal et al (1997) report that LBGs at z $ 3 are compact and, if projected to z $ 3, this population would range in half-light radius from 0B08 to 0B35 with a median size of R h ¼ 0B18. Although just over half of this range of half-light radii would be detectable at our magnitude limit, the full range of half-light radii is accessible to this sample at brighter magnitudes and failure to detect such objects may indicate a reduction in the physical scale of galaxies with increasing redshift.…”

Astrophysics in 1997

“…The closely related topic z ϭ 1.5 of the brightnesses of individual galaxies as a function of redshift was tackled by Sawicki et al (1997), who put peak brightness at . And the bits that are clustered on the sky z ϭ 3 z ϭ 3 are probably puzzle pieces that will later be put together to make galaxies like the ones here and now Lowenthal et al 1997), not protoclusters.…”