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We present results from a survey of galaxies in the fields of six z ≥ 3 damped Lyman α (Lyα) systems (DLAs) using the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). We report a high detection rate of up to |${\approx } 80{{\ \rm per\ cent}}$| of galaxies within 1000 km s−1 from DLAs and with impact parameters between 25 and 280 kpc. In particular, we discovered five high-confidence Lyα emitters associated with three DLAs, plus up to nine additional detections across five of the six fields. The majority of the detections are at relatively large impact parameters (>50 kpc) with two detections being plausible host galaxies. Among our detections, we report four galaxies associated with the most metal-poor DLA in our sample (Z / Z ⊙ = −2.33 ± 0.22), which trace an overdense structure resembling a filament. By comparing our detections with predictions from the Evolution and Assembly of GaLaxies and their Environments (EAGLE) cosmological simulations and a semi-analytic model designed to reproduce the observed bias of DLAs at z > 2, we conclude that our observations are consistent with a scenario in which a significant fraction of DLAs trace the neutral regions within haloes with a characteristic mass of |$M_{\rm h} \approx 10^{11}-10^{12}~\rm M_\odot$|⁠ , in agreement with the inference made from the large-scale clustering of DLAs. We finally show how larger surveys targeting ≈25 absorbers have the potential of constraining the characteristic masses of haloes hosting high-redshift DLAs with sufficient accuracy to discriminate between different models. [ABSTRACT FROM AUTHOR]

We compare our analysis of the baryon acoustic oscillations (BAO) feature in the correlation functions of SDSS BOSS DR12 LOWZ and CMASS galaxy samples with previous literature results. Using subsets of the data we obtain an empirical estimate of the errors on the correlation functions that are in agreement with the simulated errors of previous works. We find that the significance of BAO detection is the quantity most sensitive to the choice of the fitting range with the CMASS value decreasing from 8.0σ to 5.3σ as the fitting range is reduced. Although our measurements of DV (z) are in agreement with previous studies, we note that their CMASS 8.0σ (LOWZ 4.0σ) detection significance reduces to 4.7σ (2.8σ) in fits with their diagonal covariance terms only. We extend our BAO analysis to higher redshifts by fitting to the weighted mean of 2QDESp, SDSS DR5 UNIFORM, 2QZ, and 2SLAQ quasar correlation functions, obtaining a 7.6 per cent measurement compared to 3.9 per cent achieved by eBOSS DR14. Unlike for the LRG surveys, the larger error on quasar correlation functions implies a smaller role for nuisance parameters (accounting for scale-dependent clustering) in providing a good fit to the fiducial Λ cold dark matter model. Again we find that the eBOSS peak significance reduces from 2.8 to 1.4σ if we ignore the off-diagonal covariance matrix terms in our fitting. We conclude that for both LRGs and quasars, the reported BAO peak significances from the SDSS surveys depend sensitively on the accuracy of the covariance matrix at large separations. [ABSTRACT FROM AUTHOR]

We present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the Very Large Telescope in a quasar field that hosts a high column density damped Lyα absorber (DLA) at z ≈ 3.25. We detect Lyα emission from a nebula at the redshift of the DLA with line luminosity (27 ± 1) × 1041 erg s-1, which extends over 37 ± 1 kpc above a surface brightness limit of 6 × 10-19 erg s-1 cm-2 arcsec-2 at a projected distance of 30.5 ± 0.5 kpc from the quasar sightline. Two clumps lie inside this nebula, both with Lyα rest-frame equivalent width >50Å and with relative line-of-sight velocities aligned with two main absorption components seen in the DLA spectrum. In addition, we identify a compact galaxy at a projected distance of 19.1 ± 0.5 kpc from the quasar sightline. The galaxy spectrum is noisy but consistent with that of a star-forming galaxy at the DLA redshift.We argue that the Lyα nebula is ionized by radiation from star formation inside the two clumps, or by radiation from the compact galaxy. In either case, these data imply the presence of a structure with size ⪢50 kpc inside which galaxies are assembling, a picture consistent with galaxy formation in groups and filaments as predicted by cosmological simulations such as the EAGLE simulations. [ABSTRACT FROM AUTHOR]

We present new results on the auto- and cross-correlation functions of galaxies and OVI absorbers in a ~18 Gpc3 comoving volume at z < 1. We use a sample of 51 296 galaxies and 140 OVI absorbers in the column density range 13 ≲ logN ≲ 15 to measure twopoint correlation functions in the two dimensions transverse and orthogonal to the line of sight ξ (r⊥, r‖). We furthermore infer the corresponding 'real-space' correlation functions, ξ (r), by projecting ξ (r⊥, r‖) along r‖, and assuming a power-law form, ξ (r) = (r/r0)-γ. Comparing the results from the absorber-galaxy cross-correlation function, ξag, the galaxy autocorrelation function, ξgg, and the absorber autocorrelation function, ξaa, we constrain the statistical connection between galaxies and the metal-enriched intergalactic medium as a function of star formation activity. We also compare these results to predictions from the EAGLE cosmological hydrodynamical simulation and find a reasonable agreement. We find that: (i) OVI absorbers show very little velocity dispersion with respect to galaxies on ~ Mpc scales, likely ≲100 km s-1; (ii)OVI absorbers are less clustered, and potentially more extended around galaxies than galaxies are around themselves; (iii) on ≳100 kpc scales, the likelihood of finding OVI absorbers around star-forming galaxies is similar to the likelihood of finding OVI absorbers around non-star-forming galaxies; and (iv) OVI absorbers are either not ubiquitous to galaxies in our sample, or their distribution around them is patchy on scales ≲100 kpc (or both), at least for the column densities at which most are currently detected. [ABSTRACT FROM AUTHOR]

ABSTRACT We find that X-ray sources in the Extended Chandra Deep Field-South are strongly spatially correlated with Large APEX Bolometer Camera (LABOCA) 870 μm sources. We investigate the dependence of this correlation on X-ray flux, hardness ratio and column density, finding that specifically faint and absorbed X-ray sources are significant sub-mm emitters. In the X-ray source redshift subsample we confirm the previous result that higher luminosity sources ( LX > 1044 erg s−1) have greater 870 μm fluxes but we also find that this subsample selects against absorbed sources, faint in X-ray flux. Overall, we find that X-ray sources contribute 1.5 ± 0.1 Jy deg−2 to the sub-mm background, ≈3 per cent of the total, in agreement with the prediction of an obscured active galactic nuclei (AGN) model which also gives a reasonable fit to the bright sub-mm source counts. This non-unified model also suggests that when Compton-thick, X-ray-undetected sources are included, then the fractional AGN contribution to the sub-mm background would rise from ≈3 per cent to a total of 25-40 per cent, although in a unified model the AGN contribution would only reach ≈13 per cent, because the sub-mm flux of the X-ray sources is then more representative of the whole AGN population. Measurements of the dependence of sub-mm flux on X-ray flux, luminosity and column density all agree well with the predictions of the non-unified AGN model. Heavily absorbed, X-ray-undetected AGN could explain the further cross-correlation we find between sub-mm sources and z > 0.5 red galaxies. We conclude that sub-mm galaxies may contain the long-sought absorbed AGN population needed to explain the X-ray background. [ABSTRACT FROM AUTHOR]

We describe the construction of MegaZ-LRG, a photometric redshift catalogue of over one million luminous red galaxies (LRGs) in the redshift range with limiting magnitude . The catalogue is selected from the imaging data of the Sloan Digital Sky Survey (SDSS) Data Release 4. The 2dF-SDSS LRG and Quasar (2SLAQ) spectroscopic redshift catalogue of 13 000 intermediate-redshift LRGs provides a photometric redshift training set, allowing use ofannz, a neural network-based photometric-redshift estimator. The rms photometric redshift accuracy obtained for an evaluation set selected from the 2SLAQ sample is averaged over all galaxies, and for a brighter subsample . The catalogue is expected to contain ∼5 per cent stellar contamination. Theannz code is used to compute a refined star/galaxy probability based on a range of photometric parameters; this allows the contamination fraction to be reduced to 2 per cent with negligible loss of genuine galaxies. The MegaZ-LRG catalogue is publicly available on the World Wide Web from . [ABSTRACT FROM AUTHOR]

We discuss the construction of a photometric redshift catalogue of luminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS), emphasizing the principal steps necessary for constructing such a catalogue: (i) photometrically selecting the sample, (ii) measuring photometric redshifts and their error distributions, and (iii) estimating the true redshift distribution. We compare two photometric redshift algorithms for these data and find that they give comparable results. Calibrating against the SDSS and SDSS–2dF (Two Degree Field) spectroscopic surveys, we find that the photometric redshift accuracy isfor redshifts less than 0.55 and worsens at higher redshift (∼ 0.06 for). These errors are caused by photometric scatter, as well as systematic errors in the templates, filter curves and photometric zero-points. We also parametrize the photometric redshift error distribution with a sum of Gaussians and use this model to deconvolve the errors from the measured photometric redshift distribution to estimate the true redshift distribution. We pay special attention to the stability of this deconvolution, regularizing the method with a prior on the smoothness of the true redshift distribution. The methods that we develop are applicable to general photometric redshift surveys. [ABSTRACT FROM AUTHOR]

Using published Hubble Space Telescope ( HST) Cepheid data from 25 galaxies, we have found a correlation between the dispersion in the Cepheid period–luminosity ( P– L) relation and host galaxy metallicity, which is significant at the ≈3σ level in the V band. In the I band the correlation is less significant, although the tighter intrinsic dispersion of the P– L relation in I may make it harder to detect such a correlation in the HST sample. One possibility is that low metallicity galaxies have smaller metallicity gradients than high metallicity galaxies; if the Cepheid P– L relation has a significant dependence on metallicity then this might explain the higher P– L dispersion in the higher metallicity galaxies. A second possibility is that the increased P– L dispersion is driven by metallicity dispersion but now due to a relation between metallicity and Cepheid colour rather than luminosity. A third possibility is that the increased P– L dispersion is caused by an increase in the width of the instability strip with metallicity. Whatever the explanation, the high observed dispersions in the HST Cepheid P– L relations have the important consequence that the bias due to incompleteness in the P– L relation at faint magnitudes is more significant than previously thought. Using a maximum likelihood technique which takes into account the effect on the P– L relations of truncation by consistently defined magnitude completeness limits, we rederive the Cepheid distances to the 25 galaxies. In the case of the galaxies with the highest P– L dispersion at the largest distances, we find that the published distance modulus underestimates the true distance modulus by up to ≈0.5 mag. When both metallicity and magnitude incompleteness corrections are made, a scale error in the published Cepheid distances is seen in the sense that the published distance moduli are increasingly underestimated at larger distances. This results in the average distance modulus to the four galaxies in the Virgo cluster core increasing from to if the metallicity correction of Kennicutt et al. is assumed. For the 18 HST galaxies with good Tully–Fisher (TF) distances and the Cepheid–TF distance modulus average residual increases from to with . This indicates a significant scale error in TF distances, which reduces the previous Pierce & Tully TF estimate of to , assuming and a still uncertain Virgo infall model. Finally, for the eight HST galaxies with Type Ia supernovae (SNIa), the metallicity and incompleteness corrected Cepheid distances marginally suggest there may be a metallicity dependence of SNIa peak luminosity in the sense that metal-poor hosts have lower luminosity SNIa. Thus, SNIa Hubble diagram estimates of both H0 and q0 may therefore also require significant corrections for metallicity, once the exact sizes of the Cepheid metallicity corrections become better established. [ABSTRACT FROM AUTHOR]