Spectroscopic Observations of Lyman Break Galaxies at Redshifts ∼4, 5, and 6 in the Goods-South Field

Abstract

We report on observations of Lyman-break galaxies (LBGs) selected from the Great Observatories Origins Deep Survey (GOODS) at mean redshifts z ∼ 4, 5 and 6 (B 435 -, V 606 -and i 775 -band dropouts, respectively), obtained with the red-sensitive FORS2 spectrograph at the ESO VLT. This program has yielded spectroscopic identifications for 114 galaxies (∼ 60% of the targeted sample), of which 51 are at z ∼ 4, 31 at z ∼ 5, and 32 at z ∼ 6. We demonstrate that 1 Based on observations made at the European Southern Observatory Very Large Telescope, Paranal, Chile (ESO programme 170.A-0788 The Great Observatories Origins Deep Survey: ESO Public Observations of the SST Legacy / HST Treasury / Chandra Deep Field South). Also based on observations obtained with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under NASA contract NAS 5-26555.the adopted selection criteria are effective, identifying galaxies at the expected redshift with minimal foreground contamination. Of the 10% interlopers, 83% turn out to be Galactic stars. 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 are observed with Lyα both in emission and in absorption; when in absorption, strong interstellar lines are also observed in the spectra. The stacked spectra of Lyα absorbers and emitters also show that the former have redder UV spectra and stronger but narrower interstellar lines, a fact also observed at z ∼ 2 and 3. At z ∼ 6, sensitivity issues bias our sample towards galaxies with Lyα 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 Lyα emission lines. At fixed restframe UV luminosity, the equivalent width of the Lyα emission line is larger at higher redshifts. At all redshifts where the measurements can be reliably made, the redshift of the Lyα emission line turns out to be larger than that of the interstellar absorption lines, with a median velocity difference ∆V ∼ 400 km s −1 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 Lyα absorption appear to be more diffuse than galaxies with Lyα in emission.

Influence of physical galaxy properties on Lyαescape in star-forming galaxies

“…Composite spectra of z ∼ 3 LBGs (Shapley et al 2003) showed a trend between EW Lyα and E(B − V) where objects with strong Lyα emission also have steeper UV continua. Similar trends have been observed more recently (Vanzella et al 2009;Pentericci et al 2009;Kornei et al 2010) where LBGs that exhibit Lyα in emission tend to have bluer UV slopes than those with Lyα in absorption. Following Shapley et al (2003), Pentericci et al (2009) of extinction and noted the same trend between the mean values of EW Lyα versus stellar extinction.…”

The bright end of thez ~ 7UVluminosity function from a wide and deep HAWK-I survey

“…While this choice might give slightly underestimated fluxes for the more extended high-redshift candidates, we can easily take into account this systematic through the simulations that we use to estimate the LF (Sect. 6.1), which are based on the observed profile of LBGs with known spectroscopic redshifts 5.5 < z < 6.2 (Vanzella et al 2009) in the GOODS-S ACS images.…”

“…To avoid an excessive crowding in the simulated images, we include only 200 objects each time, after masking the regions of the images where real objects are present. As in C10, we randomly assign the light profile of one of the four most distant spectroscopically confirmed LBGs that were observed with ACS in GOODS (z = 5.5−6.2, Vanzella et al 2009) to each of our simulated galaxies, after convolving it with the relevant Hawk-I PSFs.…”

Ly$\mathsf{\alpha}$ emitters in the GOODS-S field

“…The Great Observatories Origins Deep Survey (GOODS) spectroscopic observations in the Chandra Deep Field South (Vanzella et al 2005(Vanzella et al , 2006(Vanzella et al , 2008(Vanzella et al , 2009aPopesso et al 2009) have accumulated, using the FORS2 and VIMOS instruments on ESO's Very Large Telescope, spectroscopy of essentially all accessible sources. The source GDS J033218.…”