Spectroscopic Observations of Lyman-Break Galaxies at Redshift ~ 4, 5 and 6 in the GOODS-South Field

TL;DR

This study presents spectroscopic observations of Lyman-break galaxies at redshifts 4, 5, and 6, revealing similarities in their UV spectra across redshifts and evidence of large-scale galactic winds, with implications for galaxy evolution.

Contribution

First spectroscopic confirmation of Lyman-break galaxies at z~4, 5, and 6 in GOODS-South, analyzing their spectral features and wind signatures across these epochs.

Findings

LBG spectra are similar across z~3 to 6 after accounting for selection effects.

Brighter LBGs tend to have weaker Lya emission lines.

Galaxies show large velocity offsets between Lya emission and interstellar absorption lines.

Abstract

We report on observations of Lyman-break galaxies (LBGs) selected from the Great Observatories Origins Deep Survey at mean redshift z~4, 5 and 6, obtained with FORS2 spectrograph at the ESO-VLT.This program has yielded spectroscopic identifications for 114 galaxies of which 51 are at z~4, 31 at z~5, and 32 at z~6. The adopted selection criteria are effective, identifying galaxies at the expected redshift with minimal foreground contamination. Once selection effects are properly accounted for, the rest-frame UV spectra of the higher-redshift LBGs appear to be similar to their counterparts at z~3. As at z~3, LBGs at z~4 and z~5 show Lya both in emission and in absorption; when in absorption, strong interstellar lines and red UV spectra are observed, a fact also measured at z~2 and 3. At z~6, sensitivity issues bias our sample towards galaxies with Lya in emission; nevertheless, these spectra appear to be similar to their lower-redshift counterparts. As in other studies at similar redshifts, we find clear evidence that brighter LBGs tend to have weaker Lya emission lines. At fixed rest-frame UV luminosity, the equivalent width of the Lya emission line is larger at higher redshifts. At all redshifts where the measurements can be reliably made, the redshift of the Lya emission line turns out to be larger than that of the interstellar absorption lines,with a median velocity difference DeltaV~400 km/s at z~4 and 5, consistent with results at lower redshifts. This shows that powerful, large-scale winds are common at high redshift.In general,there is no strong correlation between the morphology of the UV light and the spectroscopic properties. However, galaxies with deep interstellar absorption lines and strong Lya absorption appear to be more diffuse than galaxies with Lya in emission.(abridged)