Spectroscopic Confirmation of a Population of Normal Star-forming Galaxies at Redshifts z > 3

Abstract

We report the discovery of a substantial population of star-forming galaxies at 3.0 < ∼ z < ∼ 3.5. These galaxies have been selected using color criteria sensitive to the presence of a Lyman continuum break superposed on an otherwise very blue far-UV continuum, and then confirmed with deep spectroscopy on the W. M. Keck telescope. The surface density of galaxies brighter than R = 25 with 3.0 < ∼ z < ∼ 3.5 is 0.4 ± 0.07 galaxies arcmin −2 , approximately 1.3% of the deep counts at these magnitudes; this value applies both to "random" fields and to fields centered on known QSOs. The corresponding co-moving space density is approximately half that of luminous (L > ∼ L * ) present-day galaxies. Our sample of z > 3 galaxies is large enough that we can begin to detail the spectroscopic characteristics of the population as a whole. The spectra of the z > 3 galaxies are remarkably similar to those of nearby star-forming galaxies, the dominant features being strong low-ionization interstellar absorption lines and highionization stellar lines, often with P-Cygni profiles characteristic of Wolf-Rayet and O-star winds. Lyman α emission is generally weak (< 20Å rest equivalent width) and is absent for >50% of the galaxies. We assign approximate mass scales to the galaxies using the strengths of the heavily saturated interstellar features and find that, if the line widths are dominated by gravitational motions within the galaxies, the implied velocity dispersions are 180 ≤ σ ≤ 320 km s −1 , in the range expected for massive galaxies. The star formation rates, which can be measured directly from the far-UV continua, lie in the range 4 − 25 h −2 50 M ⊙ yr −1 (for q 0 = 0.5), with 8.5h −2 50 M ⊙ yr −1 being typical. Together with the morphological properties of the z > 3 galaxy population, which we discuss in a 1 Based in large part on observations obtained at the W.M. Keck Observatory, which is operated jointly by the

The Dawes Review 1: Kinematic Studies of Star-Forming Galaxies Across Cosmic Time

“…These are ultraviolet (UV)-selected star-forming galaxies first characterised by Steidel et al (1996) at z ß3. At these redshifts, the galaxies are observed to have low flux (i.e.…”

The most metal-poor galaxies

“…where light is generated by stars) at high redshifts has seen a tremendous progress in the last years thanks to programs employing the Lyman break technique (cf. Steidel et al 1995Steidel et al , 1996Steidel et al , 1999, and projects like the Hubble Deep Field (HDF, Williams et al 1996). Steidel and collaborators (1996) have shown that on the order of a few percent of the galaxies at faint optical magnitudes (R ∼ 25) are actively star forming galaxies at redshift greater than 3.…”

Detection of Lyman-α-emitting galaxies at redshift 4.55

“…9 At z > 1.7, where the [O ii] emission line at 3,727Å is no longer detectable in the optical window, we are beginning to find objects on the basis of their UV absorption lines. [10][11][12][13] These objects may be starbursting galaxies, in some cases with active galaxy (AGN) activity.…”