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The contribution of line-of-sight (LOS) peculiar velocities to the observed redshift of objects breaks the translational symmetry of the underlying theory, modifying the predicted two-point functions. These ‘wide-angle effects’ have mostly been studied using linear perturbation theory in the context of the multipoles of the correlation function and power spectrum. In this work, we present the first calculation of wide-angle terms in the Zeldovich approximation, which is known to be more accurate than linear theory on scales probed by the next generation of galaxy surveys. We present the exact result for dark matter and perturbatively biased tracers as well as the small angle expansion of the configuration- and Fourier-space two-point functions and the connection to the multifrequency angular power spectrum. We compare different definitions of the LOS direction and discuss how to translate between them. We show that wide-angle terms can reach tens of percent of the total signal in a measurement at low redshift in some approximations, and that a generic feature of wide-angle effects is to slightly shift the Baryon Acoustic Oscillation scale. [ABSTRACT FROM AUTHOR]

We present the first high-significance detection (4.1σ) of the Baryon Acoustic Oscillations (BAO) feature in the galaxy bispectrum of the twelfth data release (DR12) of the Baryon Oscillation Spectroscopic Survey (BOSS) constant mass sample (0.43 ≤ z ≤ 0.7). We measured the scale dilation parameter, α, using the power spectrum, bispectrum, and both simultaneously for DR12, plus 2048 MultiDark- patchy mocks in the North and South Galactic Caps (NGC and SGC, respectively), and the volume-weighted averages of those two samples (N+SGC). The fitting to the mocks validated our analysis pipeline, yielding values consistent with the mock cosmology. By fitting to the power spectrum and bispectrum separately, we tested the robustness of our results, finding consistent values from the NGC, SGC, and N+SGC in all cases. We found D V = 2032 ± 24(stat.) ± 15(sys.) Mpc, D V = 2038 ± 55(stat.) ± 15(sys.) Mpc, and D V= 2031 ± 22(stat.) ± 10(sys.) Mpc from the N+SGC power spectrum, bispectrum, and simultaneous fitting, respectively. Our bispectrum measurement precision was mainly limited by the size of the covariance matrix. Based on the fits to the mocks, we showed that if a less noisy estimator of the covariance were available, from either a theoretical computation or a larger suite of mocks, the constraints from the bispectrum and simultaneous fits would improve to 1.1 per cent (1.3 per cent with systematics) and 0.7 per cent (0.9 per cent with systematics), respectively, with the latter being slightly more precise than the power spectrum only constraints from the reconstructed field. [ABSTRACT FROM AUTHOR]

We present cosmological results from the final galaxy clustering data set of the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. Our combined galaxy sample comprises 1.2 million massive galaxies over an effective area of 9329 deg2 and volume of 18.7 Gpc3, divided into three partially overlapping redshift slices centred at effective redshifts 0.38, 0.51 and 0.61. We measure the angular diameter distance DM and Hubble parameterHfrom the baryon acoustic oscillation (BAO) method, in combinationwith a cosmic microwave background prior on the sound horizon scale, after applying reconstruction to reduce non-linear effects on the BAO feature. Using the anisotropic clustering of the pre-reconstruction density field, we measure the product DMH from the Alcock-Paczynski (AP) effect and the growth of structure, quantified by fΟ8(z), from redshift-space distortions (RSD). We combine individual measurements presented in seven companion papers into a set of consensus values and likelihoods, obtaining constraints that are tighter and more robust than those from any one method; in particular, the AP measurement from sub-BAO scales sharpens constraints from post-reconstruction BAOs by breaking degeneracy between DM and H. Combined with Planck 2016 cosmic microwave background measurements, our distance scale measurements simultaneously imply curvature ΩK = 0.0003 ± 0.0026 and a dark energy equation-of-state parameter w =-1.01 ± 0.06, in strong affirmation of the spatially flat cold dark matter (CDM) model with a cosmological constant (ΔCDM). Our RSD measurements of fs8, at 6 per cent precision, are similarly consistent with this model. When combined with supernova Ia data, we find H0 = 67.3 ± 1.0 kms-1 Mpc-1 even for our most general dark energy model, in tension with some direct measurements. Adding extra relativistic species as a degree of freedom loosens the constraint only slightly, to H0 = 67.8 ± 1.2 kms-1 Mpc-1. Assuming flat ΔCDM, we find Ωm = 0.310 ± 0.005 and H0 = 67.6 ± 0.5 kms-1 Mpc-1 and we find a 95 per cent upper limit of 0.16 eV c-2 on the neutrino mass sum. [ABSTRACT FROM AUTHOR]

Even as our measurements of cosmological parameters improve, the physical nature of the dark sector of the universe largely remains a mystery. Many effects of dark sector models are most prominent at very large scales and will rely on future galaxy surveys to elucidate. In this paper, we compare the topological properties of the large-scale dark matter distribution in a number of cosmological models using hydrodynamical simulations and the cosmological genus statistic. Genus curves are computed from z = 11 to 0 for ⋀ cold dark matter (⋀CDM), quintessence and warm dark matter (WDM) models, over a scale range of 1-20 h-1 Mpc. The curves are analysed in terms of their Hermite spectra to describe the power contained in non-Gaussian deformations to the cosmological density field. We find that the ⋀CDM and ⋀WDM models produce nearly identical genus curves indicating no topological differences in structure formation. The quintessence model, which differs solely in its expansion history, produces significant differences in the strength and redshift evolution of non-Gaussian modes associated with higher cluster abundances and lower void abundances. These effects are robust to cosmic variance and are characteristically different from those produced by tweaking the parameters of a ⋀CDM model. Given the simplicity and similarity of the models, detecting these discrepancies represents a promising avenue for understanding the effect of non-standard cosmologies on large-scale structure. [ABSTRACT FROM AUTHOR]

The redshift-space bispectrum (three point statistics) of galaxies depends on the expansion rate, the growth rate and the geometry of the Universe, and hence can be used to measure key cosmological parameters. In a homogeneous Universe, the bispectrum is a function of five variables and unlike its two point statistics counterpart - the power spectrum - which is a function of only two variables - is difficult to analyse unless the information is somehow reduced. The most commonly considered reduction schemes rely on computing angular integrals over possible orientations of the bispectrum triangle, thus reducing it to sets of function of only three variables describing the triangle shape. We use Fisher information formalism to study the information loss associated with this angular integration. Without any reduction, the bispectrum alone can deliver constraints on the growth rate parameter f that are better by a factor of 2.5 compared with the power spectrum, for a sample of luminous red galaxies expected from near future galaxy surveys at a redshift of z ~ 0.65 if we consider all the wavenumbers up to k ≤ 0.2 hMpc-1. At lower redshifts the improvement could be up to a factor of 3. We find that most of the information is in the azimuthal averages of the first three even multipoles. This suggests that the bispectrum of every configuration can be reduced to just three numbers (instead of a 2D function) without significant loss of cosmologically relevant information. [ABSTRACT FROM AUTHOR]

We apply two Bayesian hierarchical inference schemes to infer shear power spectra, shear maps and cosmological parameters from the Canada-France-Hawaii Telescope (CFHTLenS) weak lensing survey - the first application of this method to data. In the first approach, we sample the joint posterior distribution of the shear maps and power spectra by Gibbs sampling, with minimal model assumptions. In the second approach, we sample the joint posterior of the shear maps and cosmological parameters, providing a new, accurate and principled approach to cosmological parameter inference from cosmic shear data. As a first demonstration on data, we perform a two-bin tomographic analysis to constrain cosmological parameters and investigate the possibility of photometric redshift bias in the CFHTLenS data. Under the baseline ⋀CDM (⋀ cold dark matter) model, we constrain S8 = σ8(Ωm/0.3)0.5 = 0.67+0.03 -0.03 (68 per cent), consistent with previous CFHTLenS analyses but in tension with Planck. Adding neutrino mass as a free parameter, we are able to constrain ⋀ mv < 4.6 eV (95 per cent) using CFHTLenS data alone. Including a linear redshift-dependent photo-z bias Δz = p2(z - p1), we find p1 = -0.25+0.53 -0.60 and p2 = -0.15+0.17 -0.15, and tension with Planck is only alleviated under very conservative prior assumptions. Neither the non-minimal neutrino mass nor photo-z bias models are significantly preferred by the CFHTLenS (two-bin tomography) data. [ABSTRACT FROM AUTHOR]

We present a method of calibrating the properties of photometric redshift bins as part of a larger nested sampling analysis for the inference of cosmological parameters. The redshift bins are characterized by their mean and variance, which are varied as free parameters and marginalized over when obtaining the cosmological parameters. We demonstrate that the likelihood function for cross-correlations in an angular power spectrum framework tightly constrains the properties of bins such that they may be well determined, reducing their influence on cosmological parameters and avoiding the bias from poorly estimated redshift distributions. We demonstrate that even with only three photometric and three spectroscopic bins, we can recover accurate estimates of the mean redshift of a bin to within Δμ ≈ 3-4 × 10-3 and the width of the bin to Δσ ≈ 1 × 10-3 for galaxies near z = 1. This indicates that we may be able to bring down the photometric redshift errors to a level which is in line with the requirements for the next generation of cosmological experiments. [ABSTRACT FROM AUTHOR]

Since the volume accessible to galaxy surveys is fundamentally limited, it is extremely important to analyse available data in the most optimal fashion. One way of enhancing the cosmological information extracted from the clustering of galaxies is by weighting the galaxy field. The most widely used weighting schemes assign weights to galaxies based on the average local density in the region (FKP weights) and their bias with respect to the dark matter field (PVP weights). They are designed to minimize the fractional variance of the galaxy power-spectrum. We demonstrate that the currently used bias dependent weighting scheme can be further optimized for specific cosmological parameters. We develop a procedure for computing the optimal weights and test them against mock catalogues for which the values of all fitting parameters, as well as the input power-spectrum are known. We show that by applying these weights to the joint power-spectrum of emission line galaxies and luminous red galaxies from the Dark Energy Spectroscopic Instrument survey, the variance in the measured growth rate parameter can be reduced by as much as 36 per cent. [ABSTRACT FROM AUTHOR]

High-redshift radio-loud quasars are used to, among other things, test the predictions of cosmological models, set constraints on black hole growth in the early Universe and understand galaxy evolution. Prior to this paper, 20 extragalactic radio sources at redshifts above 4.5 have been imaged with very long baseline interferometry (VLBI). Here, we report on observations of an additional ten z > 4.5 sources at 1.7 and 5 GHz with the European VLBI Network, thereby increasing the number of imaged sources by 50 per cent. Combining our newly observed sources with those from the literature, we create a substantial sample of 30 z > 4.5 VLBI sources, allowing us to study the nature of these objects. Using spectral indices, variability and brightness temperatures, we conclude that of the 27 sources with sufficient information to classify, the radio emission from one source is from star formation, 13 are flat-spectrum radio quasars and 13 are steep-spectrum sources. We also argue that the steep-spectrum sources are off-axis (unbeamed) radio sources with rest-frame self-absorption peaks at or below GHz frequencies and that these sources can be classified as gigahertz peaked-spectrum and megahertz peaked-spectrum sources. [ABSTRACT FROM AUTHOR]

The power spectrum of galaxy clusters is an important probe of the cosmological model. In this paper, we develop a formalism to compute the optimal weights for the estimation of the matter power spectrum from cluster power spectrum measurements. We find a closedform analytic expression for the optimal weights, which takes into account: the cluster mass, finite survey volume effects, survey masking, and a flux limit. The optimal weights are w(M,χ) ∝ b(M,χ)/[1 + n¯h(χ)b2¯(χ)P¯(k)], where b(M, χ) is the bias of clusters of mass M at radial position χ(z), n¯h(χ) and b¯2(χ) are the expected space density and bias squared of all clusters, and P¯(k) is the matter power spectrum at wavenumber k. This result is analogous to that of Percival et al. We compare our optimal weighting scheme with mass weighting and also with the original power spectrum scheme of Feldman et al. We show that our optimal weighting scheme outperforms these approaches for both volume- and flux-limited cluster surveys. Finally, we present a new expression for the Fisher information matrix for cluster power spectrum analysis. Our expression shows that for an optimally weighted cluster survey the cosmological information content is boosted, relative to the standard approach of Tegmark. [ABSTRACT FROM AUTHOR]

We present a new 'supercalibration' technique for measuring systematic distortions in the wavelength scales of high-resolution spectrographs. By comparing spectra of 'solar twin' stars or asteroids with a reference laboratory solar spectrum, distortions in the standard thorium-argon calibration can be tracked with ~10ms-1 precision over the entire optical wavelength range on scales of both echelle orders (~50-100Å) and entire spectrographs arms (~1000-3000Å). Using archival spectra from the past 20 yr, we have probed the supercalibration history of the Very Large Telescope-Ultraviolet and Visible Echelle Spectrograph (VLT-UVES) and Keck-High Resolution Echelle Spectrograph (HIRES) spectrographs. We find that systematic errors in their wavelength scales are ubiquitous and substantial, with long-range distortions varying between typically ±200ms-1 per 1000Å. We apply a simple model of these distortions to simulated spectra that characterize the large UVES and HIRES quasar samples which previously indicated possible evidence for cosmological variations in the fine-structure constant, a. The spurious deviations in a produced by the model closely match important aspects of the VLT-UVES quasar results at all redshifts and partially explain the HIRES results, though not self-consistently at all redshifts. That is, the apparent ubiquity, size and general characteristics of the distortions are capable of significantly weakening the evidence for variations in a from quasar absorption lines. [ABSTRACT FROM AUTHOR]

Observations of redshift-space distortions in spectroscopic galaxy surveys offer an attractive method for observing the build-up of cosmological structure, which depends both on the expansion rate of the Universe and our theory of gravity. In preparation for analysis of redshift-space distortions from the Baryon Oscillation Spectroscopic Survey (BOSS) final data release, we compare a number of analytic and phenomenological models, specified in configuration space, to mock catalogues derived in different ways from several N-body simulations. The galaxies in each mock catalogue have properties similar to those of the higher redshift galaxies measured by BOSS but differ in the details of how small-scale velocities and halo occupancy are determined. We find that all of the analytic models fit the simulations over a limited range of scales while failing at small scales. We discuss which models are most robust and on which scales they return reliable estimates of the rate of growth of structure: we find that models based on some form of resummation can fit our N-body data for BOSS-like galaxies above 30h-1 Mpc well enough to return unbiased parameter estimates. [ABSTRACT FROM AUTHOR]

What are Type II-Linear supernovae (SNe II-L)? This class, which has been ill defined for decades, now receives significant attention – both theoretically, in order to understand what happens to stars in the ∼15–25 M⊙ range, and observationally, with two independent studies suggesting that they cannot be cleanly separated photometrically from the regular hydrogen-rich SNe II-P characterized by a marked plateau in their light curve. Here, we analyse the multiband light curves and extensive spectroscopic coverage of a sample of 35 SNe II and find that 11 of them could be SNe II-L. The spectra of these SNe are hydrogen deficient, typically have shallow Hα absorption, may show indirect signs of helium via strong O i λ7774 absorption, and have faster line velocities consistent with a thin hydrogen shell. The light curves can be mostly differentiated from those of the regular, hydrogen-rich SNe II-P by their steeper decline rates and higher luminosity, and we propose to define them based on their decline in the V band: SNe II-L decline by more than 0.5 mag from peak brightness by day 50 after explosion. Using our sample we provide template light curves for SNe II-L and II-P in four photometric bands. [ABSTRACT FROM PUBLISHER]

Upcoming wide-area weak lensing surveys are expensive both in time and cost and require an optimal survey design in order to attain maximum scientific returns from a fixed amount of available telescope time. The supersample covariance (SSC), which arises from unobservable modes that are larger than the survey size, significantly degrades the statistical precision of weak lensing power spectrum measurement even for a wide-area survey. Using the 1000 mock realizations of the lognormal model, which approximates the weak lensing field for a Λ-dominated cold dark matter model, we study an optimal survey geometry to minimize the impact of SSC contamination. For a continuous survey geometry with a fixed survey area, a more elongated geometry such as a rectangular shape of 1:400 side length ratio reduces the SSC effect and allows for a factor of 2 improvement in the cumulative signal-to-noise ratio (S/N) of power spectrum measurement up to ℓmax ≃ a few 103, compared to compact geometries such as squares or circles. When we allow the survey geometry to be disconnected but with a fixed total area, assuming 1 × 1 deg2 patches as the fundamental building blocks of survey footprints, the best strategy is to locate the patches with ∼15 deg separation. This separation angle corresponds to the scale at which the two-point correlation function has a negative minimum. The best configuration allows for a factor of 100 gain in the effective area coverage as well as a factor of 2.5 improvement in the S/N at high multipoles, yielding a much wider coverage of multipoles than in the compact geometry. [ABSTRACT FROM AUTHOR]

The amplitude of the thermal Sunyaev–Zel'dovich effect (tSZ) power spectrum is extremely sensitive to the abundance of the most massive dark matter haloes (galaxy clusters) and therefore to fundamental cosmological parameters that control their growth, such as σ8 and Ωm. Here we explore the sensitivity of the tSZ power spectrum to important non-gravitational (‘subgrid’) physics by employing the cosmo-OWLS suite of large-volume cosmological hydrodynamical simulations, run in both the Planck and 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) best-fitting cosmologies. On intermediate and small angular scales (ℓ ≳ 1000, or θ≲10 arcmin), accessible with the South Pole Telescope (SPT) and the Atacama Cosmology Telescope (ACT), the predicted tSZ power spectrum is highly model dependent, with gas ejection due to active galactic nuclei (AGN) feedback having a particularly large effect. However, at large scales, observable with the Planck telescope, the effects of subgrid physics are minor. Comparing the simulated tSZ power spectra with observations, we find a significant amplitude offset on all measured angular scales (including large scales), if the Planck best-fitting cosmology is assumed by the simulations. This is shown to be a generic result for all current models of the tSZ power spectrum. By contrast, if the WMAP7 cosmology is adopted, there is full consistency with the Planck tSZ power spectrum measurements on large scales and agreement at the 2σ level with the SPT and ACT measurements at intermediate scales for our fiducial AGN model, which Le Brun et al. have shown reproduces the ‘resolved’ properties of the Local Group and cluster population remarkably well. These findings strongly suggest that there are significantly fewer massive galaxy clusters than expected for the Planck best-fitting cosmology, which is consistent with recent measurements of the tSZ number counts. Our findings therefore pose a significant challenge to the cosmological parameter values preferred (and/or the model adopted) by the Planck primary cosmic microwave background analyses. [ABSTRACT FROM AUTHOR]

Determining accurate redshift distributions for very large samples of objects has become increasingly important in cosmology. We investigate the impact of extending cross-correlation based redshift distribution recovery methods to include small-scale clustering information. The major concern in such work is the ability to disentangle the amplitude of the underlying redshift distribution from the influence of evolving galaxy bias. Using multiple simulations covering a variety of galaxy bias evolution scenarios, we demonstrate reliable redshift recoveries using linear clustering assumptions well into the non-linear regime for redshift distributions of narrow redshift width. Including information from intermediate physical scales balances the increased information available from clustering and the residual bias incurred from relaxing of linear constraints. We discuss how breaking a broad sample into tomographic bins can improve estimates of the redshift distribution, and present a simple bias removal technique using clustering information from the spectroscopic sample alone. [ABSTRACT FROM AUTHOR]

This paper presents a new sample of BL Lac objects selected from a deep (30 mJy) radio survey of flat spectrum radio sources (the CLASS blazar survey). The sample is one of the largest well-defined samples in the low-power regime with a total of 130 sources of which 55 satisfy the ‘classical’ optical BL Lac selection criteria, and the rest have indistinguishable radio properties. The primary goal of this study is to establish the radio luminosity function (RLF) on firm statistical ground at low radio luminosities where previous samples have not been able to investigate. The gain of taking a peek at lower powers is the possibility to search for the flattening of the luminosity function which is a feature predicted by the beaming model but which has remained elusive to observational confirmation. In this study, we extend for the first time the BL Lac RLF down to very low radio powers ∼1022 W Hz−1, i.e. two orders of magnitude below the RLF currently available in the literature. In the process, we confirm the importance of adopting a broader, and more physically meaningful set of classification criteria to avoid the systematic missing of low-luminosity BL Lacs. Thanks to the good statistics we confirm the existence of weak but significant positive cosmological evolution for the BL Lac population, and we detect, for the first time the flattening of the RLF at L ∼ 1025 W Hz−1 in agreement with the predictions of the beaming model. [ABSTRACT FROM AUTHOR]

We place the most robust constraint to date on the scale of the turnover in the cosmological matter power spectrum using data from the WiggleZ Dark Energy Survey. We find this feature to lie at a scale of k0 = 0.0160+ 0.0035− 0.0041 (h Mpc−1) (68 per cent confidence) for an effective redshift of zeff = 0.62 and obtain from this the first ever turnover-derived distance and cosmology constraints: a measure of the cosmic distance–redshift relation in units of the horizon scale at the redshift of radiation–matter equality (rH) of DV(zeff = 0.62)/rH = 18.3+ 6.3− 3.3 and, assuming a prior on the number of extra relativistic degrees of freedom Neff = 3, constraints on the cosmological matter density parameter ΩM h2 = 0.136+ 0.026− 0.052 and on the redshift of matter–radiation equality zeq = 3274+ 631− 1260. We stress that these results are obtained within the theoretical framework of Gaussian primordial fluctuations and linear large-scale bias. With this caveat, all results are in excellent agreement with the predictions of standard ΛCDM models. Our constraints on the logarithmic slope of the power spectrum on scales larger than the turnover are bounded in the lower limit with values only as low as −1 allowed, with the prediction of P(k) ∝ k from standard ΛCDM models easily accommodated by our results. Finally, we generate forecasts to estimate the achievable precision of future surveys at constraining k0, ΩM h2, zeq and Neff. We find that the Baryon Oscillation Spectroscopic Survey should substantially improve upon the WiggleZ turnover constraint, reaching a precision on k0 of ±9 per cent (68 per cent confidence), translating to precisions on ΩM h2 and zeq of ±10 per cent (assuming a prior Neff = 3) and on Neff of + 78− 56 per cent (assuming a prior ΩM h2 = 0.135). This represents sufficient precision to sharpen the constraints on Neff from WMAP, particularly in its upper limit. For Euclid, we find corresponding attainable precisions on (k0, ΩM h2, Neff) of (3, 4, + 17− 21) per cent. This represents a precision approaching our forecasts for the Planck Surveyor. [ABSTRACT FROM PUBLISHER]

We analyse the properties of dark matter haloes in the cold-plus-warm dark matter (CWDM) cosmologies. We study their dependence on the fraction and velocity dispersion of the warm particle, keeping the free-streaming scale fixed. To this end, we consider three models with the same free-streaming: (1) a mixture of 90 per cent of CDM and 10 per cent of WDM with the mass 1 keV; (2) a mixture of 50 per cent of CDM and 50 per cent of WDM with the mass 5 keV and (3) pure WDM with the mass 10 keV. 'Warm' particles have rescaled -Dirac spectrum of primordial velocities (as non-resonantly produced sterile neutrinos would have). We compare the properties of haloes among these models and with a ...CDM with the same cosmological parameters. We demonstrate that although these models have the same free-streaming length and the suppression of matter spectra are similar at scales probed by the Lyman a forest (comoving wave-numbers k < 3-5 h Mpc-1), the resulting properties of haloes with masses below ~1011M⊙are different due to the different behaviour of matter power spectra at smaller scales. In particular, we find that while the number of galaxies remains the same as in the ...CDM case, their density profiles become much less concentrated and hence in better agreement with current observational constraints. Our results imply that a single parameter (e.g. free-streaming length) description of these models is not enough to fully capture their effects on the structure formation process. [ABSTRACT FROM AUTHOR]

ABSTRACT We present measurements of galaxy clustering from the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the Sloan Digital Sky Survey III (SDSS-III). These use the Data Release 9 (DR9) CMASS sample, which contains 264 283 massive galaxies covering 3275 square degrees with an effective redshift z = 0.57 and redshift range 0.43 < z < 0.7. Assuming a concordance ΛCDM cosmological model, this sample covers an effective volume of 2.2 Gpc3, and represents the largest sample of the Universe ever surveyed at this density [ABSTRACT FROM AUTHOR]

ABSTRACT We use a quadratic maximum likelihood (QML) method to estimate the angular power spectrum of the cross-correlation between cosmic microwave background and large-scale structure maps as well as their individual auto-spectra. We describe our implementation of this method and demonstrate its accuracy on simulated maps. We apply this optimal estimator to Wilkinson Microwave Anisotropy Probe ( WMAP) 7-yr and National Radio Astronomical Observatory (NRAO) Very Large Array Sky Survey (NVSS) data and explore the robustness of the angular power spectrum estimates obtained by the QML method. With the correction of the declination systematics in NVSS, we can safely use most of the information contained in this survey. We then make use of the angular power spectrum estimates obtained by the QML method to derive constraints on the dark energy critical density in a flat Λ cold dark matter model by different likelihood prescriptions. When using just the cross-correlation between WMAP 7-yr and NVSS maps with 1°.8 resolution, the best-fitting model has a cosmological constant of approximately 70 per cent of the total energy density, disfavouring an Einstein-de sitter universe at more than 2σ confidence level. [ABSTRACT FROM AUTHOR]

ABSTRACT Optical fibres are essential for many types of highly multiplexed and precision spectroscopy. The success of the new generation of multifibre instruments under construction to investigate fundamental problems in cosmology, such as the nature of dark energy, requires accurate modellization of the fibre system to achieve their signal-to-noise ratio (SNR) goals. Despite their simple construction, fibres exhibit unexpected behaviour including non-conservation of etendue (focal ratio degradation, FRD) and modal noise. Furthermore, new fibre geometries (non-circular or tapered) have become available to improve the scrambling properties that, together with modal noise, limit the achievable SNR in precision spectroscopy. These issues have often been addressed by extensive tests on candidate fibres and their terminations, but these are difficult and time-consuming. Modelling by ray tracing and wave analysis is possible with commercial software packages, but these do not address the more complex features, in particular FRD. We use a phase-tracking ray-tracing method to provide a practical description of FRD derived from our previous experimental work on circular fibres and apply it to non-standard fibres. This allows the relationship between scrambling and FRD to be quantified for the first time. We find that scrambling primarily affects the shape of the near-field pattern but has negligible effect on the barycentre. FRD helps to homogenize the near-field pattern but does not make it completely uniform. Fibres with polygonal cross-section improve scrambling without amplifying the FRD. Elliptical fibres, in conjunction with tapering, may offer an efficient means of image slicing to improve the product of resolving power and throughput, but the result is sensitive to the details of illumination. We also investigated the performance of fibres close to the limiting numerical aperture since this may affect the uniformity of the SNR for some prime focus fibre instrumentation. [ABSTRACT FROM AUTHOR]

ABSTRACT We obtain constraints on cosmological parameters from the spherically averaged redshift-space correlation function of the CMASS Data Release 9 (DR9) sample of the Baryonic Oscillation Spectroscopic Survey (BOSS). We combine this information with additional data from recent cosmic microwave background (CMB), supernova and baryon acoustic oscillation measurements. Our results show no significant evidence of deviations from the standard flat Λ cold dark matter model, whose basic parameters can be specified by Ωm = 0.285 ± 0.009, 100 Ωb = 4.59 ± 0.09, ns = 0.961 ± 0.009, H0 = 69.4 ± 0.8 km s−1 Mpc−1 and σ8 = 0.80 ± 0.02. The CMB+CMASS combination sets tight constraints on the curvature of the Universe, with Ω k = −0.0043 ± 0.0049, and the tensor-to-scalar amplitude ratio, for which we find r < 0.16 at the 95 per cent confidence level (CL). These data show a clear signature of a deviation from scale invariance also in the presence of tensor modes, with ns < 1 at the 99.7 per cent CL. We derive constraints on the fraction of massive neutrinos of fν < 0.049 (95 per cent CL), implying a limit of ∑ mν < 0.51 eV. We find no signature of a deviation from a cosmological constant from the combination of all data sets, with a constraint of wDE = −1.033 ± 0.073 when this parameter is assumed time-independent, and no evidence of a departure from this value when it is allowed to evolve as wDE( a) = w0 + w a(1 − a). The achieved accuracy on our cosmological constraints is a clear demonstration of the constraining power of current cosmological observations. [ABSTRACT FROM AUTHOR]

ABSTRACT We explore the ability of observations of the global brightness temperature of the 21-cm signal to constrain the reionization history and the properties of the ionizing sources. In order to describe the reionization signal, we employ either a commonly used toy model or a more realistic structure formation model that parametrizes the properties of the ionizing sources. If the structure formation model captures the actual evolution of the reionization signal, then detecting the signal is somewhat easier than it would be for the toy model; using the toy model in this case also leads to systematic errors in reconstructing the reionization history, though a sufficiently sensitive experiment should be able to distinguish between the two models. We show that under optimistic assumptions regarding systematic noise and foreground removal, 1-year observations of the global 21-cm spectrum should be able to detect a wide range of realistic models and measure the main features of the reionization history while constraining the key properties of the ionizing sources. [ABSTRACT FROM AUTHOR]

ABSTRACT We examine the mode functions of the electromagnetic field on spherically symmetric backgrounds with special attention to the subclass which allows for a foliation as open Friedmann-Lemaître (FL) space-time. It is well known that in certain scalar field theories on open FL background there can exist so-called supercurvature modes, their existence depending on parameters of the theory. Looking at specific open universe models, such as open inflation and the Milne universe, we find that no supercurvature modes are present in the spectrum of the electromagnetic field. This excludes the possibility for superadiabatic evolution of cosmological magnetic fields within these models without relying on new physics or breaking the conformal invariance of electromagnetism. [ABSTRACT FROM AUTHOR]

ABSTRACT The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM-Newton Science Archive. Its main aims are to measure cosmological parameters and trace the evolution of X-ray scaling relations. In this paper we present the first data release from the XMM Cluster Survey (XCS-DR1). This consists of 503 optically confirmed, serendipitously detected, X-ray clusters. Of these clusters, 256 are new to the literature and 357 are new X-ray discoveries. We present 463 clusters with a redshift estimate (0.06 < z < 1.46), including 261 clusters with spectroscopic redshifts. The remainder have photometric redshifts. In addition, we have measured X-ray temperatures ( TX) for 401 clusters (0.4 < TX < 14.7 keV). We highlight seven interesting subsamples of XCS-DR1 clusters: (i) 10 clusters at high redshift ( z > 1.0, including a new spectroscopically confirmed cluster at z= 1.01); (ii) 66 clusters with high TX (>5 keV); (iii) 130 clusters/groups with low TX (<2 keV); (iv) 27 clusters with measured TX values in the Sloan Digital Sky Survey (SDSS) 'Stripe 82' co-add region; (v) 77 clusters with measured TX values in the Dark Energy Survey region; (vi) 40 clusters detected with sufficient counts to permit mass measurements (under the assumption of hydrostatic equilibrium); (vii) 104 clusters that can be used for applications such as the derivation of cosmological parameters and the measurement of cluster scaling relations. The X-ray analysis methodology used to construct and analyse the XCS-DR1 cluster sample has been presented in a companion paper, Lloyd-Davies et al. [ABSTRACT FROM AUTHOR]

ABSTRACT The success of future large-scale weak-lensing surveys will critically depend on the accurate estimation of photometric redshifts of very large samples of galaxies. This in turn depends on both the quality of the photometric data and the photo- z estimators. In a previous study, we focused primarily on the impact of photometric quality on photo- z estimates and on the development of novel techniques to construct the N( z) of tomographic bins at the high level of precision required for precision cosmology, as well as the correction of issues such as imprecise corrections for Galactic reddening. We used the same set of templates to generate the simulated photometry as were then used in the photo- z code, thereby removing any effects of 'template error'. In this work we now include the effects of 'template error' by generating simulated photometric data set from actual COSMOS photometry. We use the trick of simulating redder photometry of galaxies at higher redshifts by using a bluer set of passbands on low- z galaxies with known redshifts. We find that 'template error' is a rather small factor in photo- z performance, at the photometric precision and filter complement expected for all-sky surveys. With only a small subset of training galaxies with spectroscopic redshifts, it is in principle possible to construct tomographic redshift bins whose mean redshift is known, from photo- z alone, to the required accuracy of |Δ〈 z〉|≤ 0.002(1 + z). [ABSTRACT FROM AUTHOR]

ABSTRACT The success of future large-scale weak-lensing surveys will critically depend on the accurate estimation of photometric redshifts of very large samples of galaxies. This in turn depends on both the quality of the photometric data and the photo- z estimators. In a previous study, we focused primarily on the impact of photometric quality on photo- z estimates and on the development of novel techniques to construct the N( z) of tomographic bins at the high level of precision required for precision cosmology, as well as the correction of issues such as imprecise corrections for Galactic reddening. We used the same set of templates to generate the simulated photometry as were then used in the photo- z code, thereby removing any effects of 'template error'. In this work we now include the effects of 'template error' by generating simulated photometric data set from actual COSMOS photometry. We use the trick of simulating redder photometry of galaxies at higher redshifts by using a bluer set of passbands on low- z galaxies with known redshifts. We find that 'template error' is a rather small factor in photo- z performance, at the photometric precision and filter complement expected for all-sky surveys. With only a small subset of training galaxies with spectroscopic redshifts, it is in principle possible to construct tomographic redshift bins whose mean redshift is known, from photo- z alone, to the required accuracy of |Δ〈 z〉|≤ 0.002(1 + z). [ABSTRACT FROM AUTHOR]

ABSTRACT Before it becomes a sensitive probe of the epoch of reionization, the dark ages and fundamental physics, 21-cm tomography must successfully contend with the issue of foreground contamination. Broad-band foreground sources are expected to be roughly 4 orders of magnitude larger than any cosmological signals, so precise foreground models will be necessary. Such foreground models often contain a large number of parameters, reflecting the complicated physics that governs foreground sources. In this paper, we concentrate on spectral modelling (neglecting, for instance, bright point source removal from spatial maps) and show that 21-cm tomography experiments will likely not be able to measure these parameters without large degeneracies, simply because the foreground spectra are so featureless and generic. However, we show that this is also an advantage, because it means that the foregrounds can be characterized to a high degree of accuracy once a small number of parameters (likely three or four, depending on one's instrumental specifications) are measured. This provides a simple understanding for why 21-cm foreground subtraction schemes are able to remove most of the contaminants by suppressing just a small handful of simple spectral forms. In addition, this suggests that the foreground modelling process should be relatively simple and will likely not be an impediment to the foreground subtraction schemes that are necessary for a successful 21-cm tomography experiment. [ABSTRACT FROM AUTHOR]

ABSTRACT We have studied a sample of 1084 intervening absorption systems with 2.15 ≤ zab≤ 5.2, having in the spectra of quasi-stellar objects (QSOs) in Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7), with the aim of understanding the nature and abundance of the dust and the chemical abundances in the damped Lyman α (DLA) absorbers. Composite spectra were constructed for the full sample and several subsamples, chosen on the basis of absorber and QSO properties. Average extinction curves were obtained for the samples by comparing their geometric mean composite spectra with those of two samples of QSOs, matching in zem and i magnitude with the DLA sample, one sample without any absorbers along their lines of sight and the other without any DLAs along their lines of sight irrespective of the presence of other absorption systems. We also derived relative extinction curves of several pairs of subsamples. While the average reddening in the DLA sample is small, we find definite evidence for the presence of dust in subsamples based on absorber properties, in particular the strength of metal absorption lines. DLAs along lines of sight to QSOs which are not colour selected are found to be more dusty compared to those along the lines of sight to the more numerous colour-selected QSOs. From these studies and from the strengths of absorption lines in the composite spectra, we conclude that ≤10 per cent of the DLAs in SDSS DR7 cause significant reddening, have stronger absorption lines and have higher abundances as compared to the rest of the sample. The rest of the sample shows little reddening. While, due to the dominant colour selection method used to target QSOs in the SDSS DR7, this fraction of 10 per cent likely represents a lower limit for the global fraction of dusty DLAs at high z, it is also possible that the dust grain sizes at high redshifts are larger, giving rise to a flat extinction curve over the observed range of wavelengths. [ABSTRACT FROM AUTHOR]

ABSTRACT The intrinsic alignment (IA) of galaxies has been shown to be a significant barrier to precision cosmic shear measurements. Recently, Zhang proposed a self-calibration technique for the power spectrum to calculate the induced gravitational shear-galaxy intrinsic ellipticity correlation (GI) in weak lensing surveys with photo- z measurements, which is expected to reduce the IA contamination by at least a factor of 10 for currently proposed surveys. We confirm this using an independent analysis and propose an expansion to the self-calibration technique for the bispectrum in order to calculate the dominant IA gravitational shear-gravitational shear-intrinsic ellipticity correlation (GGI) contamination. We first establish an estimator to extract the galaxy density-density-intrinsic ellipticity (ggI) correlation from the galaxy ellipticity-density-density measurement for a photo- z galaxy sample. We then develop a relation between the GGI and ggI bispectra, which allows for the estimation and removal of the GGI correlation from the cosmic shear signal. We explore the performance of these two methods, compare to other possible sources of error, and show that the GGI self-calibration technique can potentially reduce the IA contamination by up to a factor of 5-10 for all but a few bin choices, thus reducing the contamination to the per cent level. The self-calibration is less accurate for adjacent bins, but still allows for a factor of 3 reduction in the IA contamination. The self-calibration thus promises to be an efficient technique to isolate both the two-point and three-point intrinsic alignment signals from weak lensing measurements. [ABSTRACT FROM AUTHOR]

ABSTRACT We used a suite of numerical cosmological simulations in order to investigate the effect of gas cooling and star formation on the large-scale matter distribution. The simulations follow the formation of cosmic structures in five different dark energy models: the fiducial Λcold dark matter (ΛCDM) cosmology and four models where the dark energy density is allowed to have a non-trivial redshift evolution. Each simulation includes a variety of gas physics, ranging from radiative cooling to UV heating and supernova feedback [although the active galactic nuclei (AGN) feedback is not incorporated]. Moreover, for each cosmology we have a control run with dark matter only, in order to allow a direct assessment of the effect of baryonic processes. We found that the power spectra of gas and stars, as well as the total matter power spectrum, are in qualitative agreement with the results of previous works not including the AGN effects in the framework of the fiducial model, although several quantitative differences exist. We used the physically motivated halo model in order to investigate the backreaction of gas and stars on the dark matter distribution, finding that it is very well reproduced by simply increasing the average dark matter halo concentration by 17 per cent, irrespective of the mass. This is in agreement with the cooling of gas dragging dark matter in the very centre of haloes, as well as adiabatic contraction steepening the relative potential wells. Moving to model universes dominated by dynamical dark energy, it turns out that they introduce a specific signature on the power spectra of the various matter components, which is qualitatively independent of the exact cosmology considered. This generic shape is well captured by the halo model if we blindly consider the cosmology dependences of the halo mass function, bias and concentration. However, the details of the dark matter power spectrum can be precisely captured only at the cost of a few slight modifications to the ingredients entering in the halo model. The backreaction of baryons on to the dark matter distribution works pretty much in the same way as in the reference ΛCDM model, in the sense that it is very well described by an increment in the average halo concentration. None the less, this increment is less pronounced than in the fiducial model (only ∼10 per cent), in agreement with a series of other clues pointing towards the fact that star formation is less efficient when dark energy displays a dynamical evolution. [ABSTRACT FROM AUTHOR]

ABSTRACT We study the morphology and size of the luminous and massive galaxies at 0.3 < z < 0.7 targeted in the Baryon Oscillation Spectroscopic Survey (BOSS) using publicly available Hubble Space Telescope ( HST) imaging, and catalogues, from the COSMic Origins Survey (COSMOS). Our sample (240 objects) provides a unique opportunity to check the visual morphology of these galaxies which were targeted based solely on stellar population modelling. We find that the majority of BOSS galaxies (74 ± 6 per cent) possess an early-type morphology (elliptical or lenticular), while the remainder have a late-type (spiral disc) morphology. This is as expected from the goals of the BOSS target selection which aimed to predominantly select slowly evolving galaxies, for use as cosmological probes, while still obtaining a fair fraction of actively star-forming galaxies for galaxy evolution studies. We show that a colour cut of ( g− i) > 2.35 is able to select a sub-sample of BOSS galaxies with ≥90 per cent early-type morphology and thus more comparable to the earlier Luminous Red Galaxy (LRG) samples of Sloan Digital Sky Survey (SDSS)-I/II. The remaining ≃10 per cent of galaxies above this ( g− i) cut have a late-type morphology and may be analogous to the 'passive spirals' found at lower redshift. We find that 23 ± 4 per cent of the early-type BOSS galaxies are unresolved multiple systems in the SDSS imaging. We estimate that at least 50 per cent of these multiples are likely real associations and not projection effects and may represent a significant 'dry merger' fraction. We study the SDSS pipeline sizes of BOSS galaxies which we find to be systematically larger (by 40 per cent) than those measured from HST images, and provide a statistical correction for the difference. These details of the BOSS galaxies will help users of the BOSS data fine-tune their selection criteria, dependent on their science applications. For example, the main goal of BOSS is to measure the cosmic distance scale and expansion rate of the Universe to per cent level precision - a point where systematic effects due to the details of target selection may become important. [ABSTRACT FROM AUTHOR]

ABSTRACT Molecular hydrogen transitions in quasar spectra can be used to constrain variation in the proton-to-electron mass ratio, μ≡ mp/ me, at high redshifts ( z ≳ 2). We present here an analysis of a new spectrum of the quasar Q0528−250, obtained on Very Large Telescope (VLT)/Ultraviolet and Visual Echelle Spectrograph (UVES), and analyse the well-known H2 absorber at z = 2.811 in this spectrum. For the first time we detect deuterated molecular hydrogen (HD) in this system with a column density of log10( N/cm−2) = 13.27 ± 0.07; HD is sensitive to variation in μ, and so we include it in our analysis. Using 76 H2 and seven HD transitions we constrain variation in μ from the current laboratory value to be Δμ/μ= (0.3 ± 3.2stat± 1.9sys) × 10−6, which is consistent with no cosmological variation in μ, as well as with previous results from other H2/HD absorbers. The main sources of systematic uncertainty relate to accurate wavelength calibration of the spectra and the re-dispersion of multiple telescope exposures on to the one pixel grid. [ABSTRACT FROM AUTHOR]

ABSTRACT The next frontier of Lyα forest studies is the reconstruction of three-dimensional (3D) correlations from a dense sample of background sources. The measurement of 3D correlations has the potential to improve constraints on fundamental cosmological parameters, ionizing background models and the re-ionization history. This study addresses the sensitivity of spectroscopic surveys to 3D correlations in the Lyα forest. We show that the sensitivity of a survey to this signal can be quantified by just a single number, a noise-weighted number density of sources on the sky. We investigate how the sensitivity of a spectroscopic quasar (or galaxy) survey scales as a function of its depth, area and redshift. We propose a simple method for weighting sightlines with varying signal-to-noise ratio (S/N) levels to estimate the correlation function, and we show that this estimator generally performs nearly as well as the minimum-variance quadratic estimator. In addition, we show that the sensitivity of a quasar survey to the flux correlation function is generally maximized if it observes each field just long enough to achieve S/N ≈ 2 in a 1-Å pixel on an L* quasar while acquiring spectra for all quasars with L > L*: little is gained by integrating longer on the same targets or by including fainter quasars. We quantify how these considerations relate to constraints on the angular diameter distance, the curvature of space-time and the re-ionization history. [ABSTRACT FROM AUTHOR]

Type Ia supernovae (SNe Ia) spectra are compared using the coefficient of the largest wavelet scale in their decomposition. Two distinct subgroups have been identified, and their occurrence is discussed with regards to the use of SNe Ia as cosmological probes. Apart from the group of normal SNe, another trend characterized by intrinsically redder colours consists of many different SN events, which exhibit diverse properties. These include the interaction with the circumstellar material and the existence of a specific shell structure in or surrounding the SN ejecta or super-Chandrasekhar mass progenitors. Compared with normal objects, these SNe may violate the standard width-luminosity correction. This could influence the cosmological results if these are all calibrated equally, as their fraction among SNe Ia is not negligible when performing precision cosmology. Using the largest wavelet scale coefficient in combination with long-baseline colours, we show how to disentangle the SN intrinsic colour from the part that corresponds to the reddening as a result of dust extinction in the host galaxy in the colour parameter c. We discuss how the intrinsic colour differences may explain the different reddening laws for two subsamples. There are wavelength intervals for which the measured largest scale coefficient is invariant to the additional extinction applied to a spectrum. A combination of wavelet coefficients measured in different wavelength intervals can be used to develop a technique that allows for the estimation of extinction. [ABSTRACT FROM AUTHOR]

We present the initial imaging and spectroscopic data acquired as part of the Very Large Telescope (VLT) VIMOS Lyman-break galaxy Survey. UBR (or UBVI) imaging covers five arcmin fields centred on bright quasi-stellar objects (QSOs), allowing galaxy candidates to be selected using the Lyman-break technique. We performed spectroscopic follow-up using VLT VIMOS, measuring redshifts for Lyman-break galaxies and QSOs from a total of 19 VIMOS pointings. From the galaxy spectra, we observe a velocity offset between the interstellar absorption and Lyman α emission-line redshifts, consistent with previous results. Using the photometric and spectroscopic catalogues, we have analysed the galaxy clustering at . The angular correlation function, , is well fitted by a double power law with clustering scalelength, and slope for and with at larger scales. Using the redshift sample we estimate the semiprojected correlation function, and, for a power law, find for the VLT sample and for a combined VLT+Keck sample. From and , and assuming the above models, we find that the combined VLT and Keck surveys require a galaxy pairwise velocity dispersion of , higher than assumed by previous authors. We also measure a value for the gravitational growth rate parameter of , again higher than that previously found and implying a low value for the bias of . This value is consistent with the galaxy clustering amplitude which gives , assuming the standard cosmology, implying that the evolution of the gravitational growth rate is also consistent with Einstein gravity. Finally, we have compared our Lyman-break galaxy clustering amplitudes with lower redshift measurements and find that the clustering strength is not inconsistent with that of low-redshift spirals for simple 'long-lived' galaxy models. [ABSTRACT FROM AUTHOR]

We study supernova-driven galactic outflows as a mechanism for injecting turbulence in the intergalactic medium (IGM) far from galaxies. To this aim, we follow the evolution of a -M galaxy along its merger tree, with carefully calibrated prescriptions for star formation and wind efficiencies. At , the majority of the bubbles around galaxies are old (ages 1 Gyr), that is, they contain metals expelled by their progenitors at earlier times; their filling factor increases with time, reaching about 10 per cent at . The energy deposited by these expanding shocks in the IGM is predominantly in kinetic form (mean energy density of 1 eV cm, about two to three times the thermal one), which is rapidly converted in disordered motions by instabilities, finally resulting in a fully developed turbulent spectrum whose evolution is followed through a spectral transfer function approach. The derived mean IGM turbulent Doppler parameter, , peaks at at about 1.5 km s with the maximum km s. The shape of the distribution does not significantly evolve with redshift but undergoes a continuous shift towards lower values with time, as a result of bubble ageing. We also find a clear trend of decreasing with and a more complex dependence on resulting from the age spread of the bubbles. We have attempted a preliminary comparison with the data, hampered by the scarcity of the latter and by the challenge provided by the subtraction of peculiar and thermal motions. Finally, we comment on the implications of turbulence for various cosmological studies. [ABSTRACT FROM AUTHOR]

Here we present a number of improvements to weak lensing 3D power spectrum analysis, 3D cosmic shear, that uses the shape and redshift information of every galaxy to constrain cosmological parameters. We show how photometric redshift probability distributions for individual galaxies can be directly included in this statistic with no averaging. We also include the Limber approximation, considerably simplifying full 3D cosmic shear analysis, and we investigate its range of applicability. Finally we show the relationship between weak lensing tomography and the 3D cosmic shear field itself; the steps connecting them being the Limber approximation, a harmonic-space transform and a discretization in wavenumber. Each method has its advantages; 3D cosmic shear analysis allows straightforward inclusion of all relevant modes, thus ensuring minimum error bars, and direct control of the range of physical wavenumbers probed, to avoid the uncertain highly non-linear regime. On the other hand, tomography is more convenient for checking systematics through direct investigation of the redshift dependence of the signal. Finally, for tomography, we suggest that the angular modes probed should be redshift dependent, to recover some of the 3D advantages. [ABSTRACT FROM AUTHOR]

ABSTRACT A coupling between a scalar field (representing the dark energy) and dark matter could produce rich phenomena in cosmology. It affects cosmic structure formation mainly through the fifth force, a velocity-dependent force that acts parallel to particle's direction of motion and proportional to its speed, an effective rescaling of the particle masses and a modified background expansion rate. In many cases, these effects entangle and it is difficult to see which is the dominant one. Here, we perform N-body simulations to study their qualitative behaviour and relative importance in affecting the key structure formation observables, for a model with exponential scalar field coupling. We find that the fifth force, a prominent example of the scalar-coupling effects, is far less important than the rescaling of particle mass or the modified expansion rate in its effects on the matter power spectrum and mass function. In particular, the rescaling of particle masses is shown to be the key factor leading to less concentration of particles in haloes than in Λcold dark matter, a pattern which is also observed in previous independent coupled scalar field simulations. [ABSTRACT FROM AUTHOR]

We have studied power density spectra (PDS) of 206 long gamma-ray bursts. We fitted the PDS with a simple power law and extracted the exponent of the power law (α) and the noise-crossing threshold frequency ( f). We find that the distribution of the extracted α peaks around −1.4 and that of f around 1 Hz. In addition, based on a subset of 58 bursts with known redshifts, we show that the redshift-corrected threshold frequency is positively correlated with the isotropic peak luminosity. The correlation coefficient is . [ABSTRACT FROM AUTHOR]

In the coming decade, low-frequency radio arrays will begin to probe the epoch of reionization via the redshifted 21-cm hydrogen line. Successful interpretation of these observations will require effective statistical techniques for analysing the data. Due to the difficulty of these measurements, it is important to develop techniques beyond the standard power-spectrum analysis in order to offer independent confirmation of the reionization history, probe different aspects of the topology of reionization and have different systematic errors. In order to assess the promise of probability distribution functions (PDFs) as statistical analysis tools in 21-cm cosmology, we first measure the 21-cm brightness temperature (one-point) PDFs in six different reionization simulations. We then parametrize their most distinct features by fitting them to a simple model. Using the same simulations, we also present the first measurements of difference PDFs in simulations of reionization. We find that while these statistics probe the properties of the ionizing sources, they are relatively independent of small-scale, subgrid astrophysics. We discuss the additional information that the difference PDF can provide on top of the power spectrum and the one-point PDF. [ABSTRACT FROM AUTHOR]

Globular clusters were thought to be simple stellar populations, but recent photometric and spectroscopic evidence suggests that the clusters' early formation history was more complicated. In particular, clusters show star-to-star abundance variations, and multiple sequences in their colour–magnitude diagrams. These effects seem to be restricted to globular clusters, and are not found in open clusters or the field. In this paper, we combine the two competing models for these multiple populations and include a consideration of the effects of stellar collisions. Collisions are one of the few phenomena which occur solely in dense stellar environments like (proto)globular clusters. We find that runaway collisions between massive stars can produce material which has abundances comparable to the observed second generations, but that very little total mass is produced by this channel. We then add the contributions of rapidly rotating massive stars (under the assumption that massive stars are spun up by collisions and interactions), and the contribution of asymptotic giant branch stars. We find that collisions can help produce the extreme abundances which are seen in some clusters. However, the total amount of material produced in these generations is still too small (by at least a factor of 10) to match the observations. We conclude with a discussion of the additional effects which probably need to be considered to solve this particular problem. [ABSTRACT FROM AUTHOR]

We performed a spectroscopic galaxy survey, complete to ≤ 20.3 ( at ), within arcsec2 of the quasar Q1127–145 . The Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph (UVES) quasar spectrum contains three Mg ii absorption systems. We obtained eight new galaxy redshifts, adding to the four previously known, and galaxy star formation rates (SFRs) and metallicities were computed where possible. A strong Mg ii system [ Å], which is a known damped Lyman α absorber (DLA), had three previously identified galaxies; we found two additional galaxies associated with this system. These five galaxies form a group with diverse properties, such as a luminosity range of , an impact parameter range of and a velocity dispersion of km s−1. The DLA group galaxy redshifts span beyond the 350 km s−1 velocity spread of the metallic absorption lines of the DLA itself. The two brightest group galaxies have SFRs of ∼ −1 and should not have strong winds. We have sufficient spectroscopic information to directly compare three of the five group galaxies' (emission-line) metallicities with the DLA (absorption) metallicity: the DLA metallicity is one-tenth solar, substantially lower than the three galaxies' metallicity which ranges between less than 1/2 solar to solar. Hubble Space Telescope ( HST)/Wide Field Planetary Camera 2 (WFPC-2) imaging shows perturbed morphologies for the three brightest group galaxies, with tidal tails extending ∼25 kpc. We favour a scenario where the DLA absorption originates from tidal debris in the group environment. Another absorber exhibits weak Mg ii absorption [ Å] and had a previously identified galaxy at a similar redshift. We have identified a second galaxy associated with this system. Both galaxies have solar metallicities and unperturbed morphologies in the HST/WFPC-2 image. The SFR of one galaxy is much lower than that expected for strong outflows. Finally, we have also identified five galaxies at large impact parameters with no associated Mg ii absorption [ mÅ, 3σ] in the spectrum of Q1127–145. [ABSTRACT FROM AUTHOR]

We address the question of whether the formation of high-mass stars is similar to or differs from that of solar mass stars through new molecular line observations and modelling of the accretion flow around the massive protostar IRAS20126+4104. We combine new observations of NH3(1,1) and (2,2) made at the Very Large Array (VLA), new observations of CH3CN(13–12) made at the Submillimeter Array, previous VLA observations of NH3(3,3) and NH3(4,4) and previous Plateau de Bure observations of C34S(2–1), C34S(5–4) and CH3CN(12–11) to obtain a data set of molecular lines covering 15–419 K in excitation energy. We compare these observations against simulated molecular line spectra predicted from a model for high-mass star formation based on a scaled-up version of the standard disc–envelope paradigm developed for accretion flows around low-mass stars. We find that in accord with the standard paradigm, the observations require both a warm, dense, rapidly rotating disc and a cold, diffuse infalling envelope. This paper suggests that accretion processes around stars are similar to those of solar mass stars. [ABSTRACT FROM AUTHOR]

One of the aims of the Low Frequency Array (LOFAR) Epoch of Reionization (EoR) project is to measure the power spectrum of variations in the intensity of redshifted 21-cm radiation from the EoR. The sensitivity with which this power spectrum can be estimated depends on the level of thermal noise and sample variance, and also on the systematic errors arising from the extraction process, in particular from the subtraction of foreground contamination. We model the extraction process using realistic simulations of the cosmological signal, the foregrounds and noise, and so estimate the sensitivity of the LOFAR EoR experiment to the redshifted 21-cm power spectrum. Detection of emission from the EoR should be possible within 360 h of observation with a single station beam. Integrating for longer, and synthesizing multiple station beams within the primary (tile) beam, then enables us to extract progressively more accurate estimates of the power at a greater range of scales and redshifts. We discuss different observational strategies which compromise between depth of observation, sky coverage and frequency coverage. A plan in which lower frequencies receive a larger fraction of the time appears to be promising. We also study the nature of the bias which foreground fitting errors induce on the inferred power spectrum and discuss how to reduce and correct for this bias. The angular and line-of-sight power spectra have different merits in this respect, and we suggest considering them separately in the analysis of LOFAR data. [ABSTRACT FROM AUTHOR]