The VLT LBG redshift survey - V. Characterizing the z = 3.1 Lyman α emitter population

Abstract

We present a survey of z ~ 3 Lyα emitters (LAEs) within the fields of the VLT Lyman break galaxies (LBG) redshift survey. The data encompass five independent survey fields co-spatial with spectroscopic LBG data and covering a larger total area than previously analysed for LAE number counts and clustering. This affords an improved analysis over previous work by minimizing the effects of cosmic variance and allowing the cross-clustering analysis of LAEs and LBGs. Our photometric sample consists of ≈600 LAE candidates, over an area of 1.07 deg2, with equivalent widths of ≳65 Å and a flux limit of ≈2 × 10-17 erg cm-2 s-1. From spectroscopic follow-up, we measured a success rate of 78 ± 18 per cent. We find the R-band continuum luminosity function to be ~10 times lower than the luminosity function of LBGs at this redshift, consistent with previous studies. Exploiting the large area of the survey, we estimate the LAE auto-correlation function and find a clustering length of r0 = 2.86 ± 0.33 h-1 Mpc, low compared to the z ~ 3 LBG population, but somewhat higher than previous LAE measurements. This corresponds to a median halo mass of MDM = 1011.0±0.3 h-1 M⊙. We present an analysis of clustering length versus continuum magnitude and find that the measurements for LAEs and LBGs are consistent at faint magnitudes. Our combined data set of LAEs and LBGs allows us to measure, for the first time, the LBG-LAE cross-correlation, finding a clustering length of r0 = 3.29 ± 0.57 h-1 Mpc and a LAE halo mass of 1011.1±0.4 h-1 M⊙. Overall, we conclude that LAEs inhabit primarily low-mass haloes, but form a relatively small proportion of the galaxy population found in such haloes.