The Very Large Telescope Lyman-Break Galaxy Redshift Survey – IV. Gas and galaxies at z ∼ 3 in observations and simulations

We use a combination of observations and simulation to study the relationship between star-forming galaxies and the intergalactic medium at z ≈ 3. The observed star-forming galaxy sample is based on spectroscopic redshift data taken from a combination of Very Large Telescope (VLT) Lyman-break galaxy (LBG) Redshift Survey (VLRS) data and Keck Low-Resolution Imaging Spectrometer (LRIS) observations in fields centred on bright background quasi-stellar objects (QSOs), whilst the simulation data is taken from the Galaxies–Intergalactic Medium Interaction Calculation (GIMIC). In the simulation, we find that the dominant peculiar velocities are in the form of large-scale coherent motions of gas and galaxies. Gravitational infall of galaxies towards one another is also seen, consistent with expectations from linear theory. At smaller scales, the root-mean-square (RMS) peculiar velocities in the simulation overpredict the difference between the simulated real- and z-space galaxy correlation functions. Peculiar velocity pairs with separations smaller than 1 h−1 Mpc have a smaller dispersion and explain the z-space correlation function better. The Lyα auto- and cross-correlation functions in the GIMIC simulation appear to show infall smaller than implied by the expected βLyα ≈ 1.3 (McDonald et al.). There is a possibility that the reduced infall may be due to the galaxy-wide outflows implemented in the simulation. The main challenge in comparing these simulated results with the observed Keck + VLRS correlation functions comes from the presence of velocity errors for the observed LBGs, which dominate at ≲ 1 h− 1 Mpc scales. When these are taken into account, the observed LBG correlation functions are well matched by the high amplitude of clustering, shown by higher mass (M* > 109 M⊙) galaxies in the simulation. The simulated cross-correlation function shows similar neutral gas densities around galaxies to those seen in the observations. The simulated and observed Lyα z-space autocorrelation functions again agree better with each other than with the βLyα ≈ 1.3 infall model. Our overall conclusion is that, at least in the simulation, gas and galaxy peculiar velocities are generally towards the low end of expectation. Finally, little direct evidence is seen in either simulation or observations for high transmission near galaxies due to feedback, in agreement with previous results

The VLT LBG redshift survey – VI. Mapping H i in the proximity of z ∼ 3 LBGs with X-Shooter

We present an analysis of the spatial distribution and dynamics of neutral hydrogen gas around galaxies using new X-Shooter observations of z ∼ 2.5–4 quasars. Adding the X-Shooter data to our existing data set of high-resolution quasar spectroscopy, we use a total sample of 29 quasars alongside ∼1700 Lyman Break Galaxies (LBGs) in the redshift range 2 ≲ z ≲ 3.5. We measure the Lyα forest auto-correlation function, finding a clustering length of s0 = 0.081 ± 0.006 h−1 Mpc, and the cross-correlation function with LBGs, finding a cross-clustering length of s0 = 0.27 ± 0.14 h−1 Mpc and power-law slope γ = 1.1 ± 0.2. Our results highlight the weakly clustered nature of neutral hydrogren systems in the Lyα forest. Building on this, we make a first analysis of the dependence of the clustering on absorber strength, finding a clear preference for stronger Lyα forest absorption features to be more strongly clustered around the galaxy population, suggesting that they trace on average higher mass haloes. Using the projected and 2-D cross-correlation functions, we constrain the dynamics of Lyα forest clouds around z ∼ 3 galaxies. We find a significant detection of large-scale infall of neutral hydrogen, with a constraint on the Lyα forest infall parameter of βF = 1.02 ± 0.22

The Role of Galaxies and AGN in Reionising the IGM - I: Keck Spectroscopy of 5 < z < 7 Galaxies in the QSO Field J1148+5251

We introduce a new method for determining the influence of galaxies and active galactic nuclei (AGN) on the physical state of the intergalactic medium (IGM) at high redshift and illustrate its potential via a first application to the field of the $z=6.42$ QSO J1148+5251. By correlating the spatial positions of spectroscopically-confirmed Lyman break galaxies (LBGs) with fluctuations in the Lyman alpha forest seen in the high signal-to-noise spectrum of a background QSO, we provide a statistical measure of the typical escape fraction of Lyman continuum photons close to the end of cosmic reionisation. Here we use Keck DEIMOS spectroscopy to locate 7 colour-selected LBGs in the redshift range $5.3\lesssim z\lesssim 6.4$ and confirm a faint $z=5.701$ AGN. We then examine the spatial correlation between this sample and Ly$\alpha$/Ly$\beta$ transmission fluctuations in a Keck ESI spectrum of the QSO. Interpreting the statistical HI proximity effect as arising from faint galaxies clustered around the detected LBGs, we translate the observed mean Ly$\alpha$ transmitted flux around an average detected LBG into a constraint on the mean escape fraction $\langle f_{\rm esc}\rangle\geq0.08$ at $z\simeq6$. We also report evidence of the individual transverse HI proximity effect of a $z=6.177$ luminous LBG via a Ly$\beta$ transmission spike and two broad Ly$\alpha$ transmission spikes around the $z=5.701$ AGN. We discuss the possible origin of such associations which suggest that while faint galaxies are primarily driving reionisation, luminous galaxies and AGN may provide important contributions to the UV background or thermal fluctuations of the IGM at $z\simeq6$. Although a limited sample, our results demonstrate the potential of making progress using this method in resolving one of the most challenging aspects of the contribution of galaxies and AGN to cosmic reionisation.Comment: 21 pages, 16 figures, the version accepted in MNRA

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

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

The VLT LBG Redshift Survey - III. The clustering and dynamics of Lyman-break galaxies at z~3

We present a catalogue of 2135 galaxy redshifts from the VLT LBG Redshift Survey (VLRS), a spectroscopic survey of z ≈ 3 galaxies in wide fields centred on background quasi-stellar objects. We have used deep optical imaging to select galaxies via the Lyman-break technique. Spectroscopy of the Lyman-break galaxies (LBGs) was then made using the Very Large Telescope (VLT) Visible Multi-Object Spectrograph (VIMOS) instrument, giving a mean redshift of z = 2.79. We analyse the clustering properties of the VLRS sample and also of the VLRS sample combined with the smaller area Keck-based survey of Steidel et al. From the semiprojected correlation function, wp(σ), for the VLRS and combined surveys, we find that the results are well fit with a single power-law model, with clustering scale lengths of r0 = 3.46 ± 0.41 and 3.83 ± 0.24 h−1 Mpc, respectively. We note that the corresponding combined ξ(r) slope is flatter than for local galaxies at γ = 1.5–1.6 rather than γ = 1.8. This flat slope is confirmed by the z–space correlation function, ξ(s), and in the range 10 < s < 100 h−1 Mpc the VLRS shows an ≈2.5σ excess over the Λ cold dark matter (ΛCDM) linear prediction. This excess may be consistent with recent evidence for non-Gaussianity in clustering results at z ≈ 1. We then analyse the LBG z–space distortions using the 2D correlation function, ξ(σ, π), finding for the combined sample a large-scale infall parameter of β = 0.38 ± 0.19 and a velocity dispersion of ⟨w2z⟩−−−−√=420+140−160kms−1. Based on our measured β, we are able to determine the gravitational growth rate, finding a value of f(z = 3) = 0.99 ± 0.50 (or fσ8 = 0.26 ± 0.13), which is the highest redshift measurement of the growth rate via galaxy clustering and is consistent with ΛCDM. Finally, we constrain the mean halo mass for the LBG population, finding that the VLRS and combined sample suggest mean halo masses of log(MDM/M⊙) = 11.57 ± 0.15 and 11.73 ± 0.07, respectively