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The apparent angular positions of quasars are deflected on the sky by the gravitational field sourced by foreground matter. This weak lensing effect is measurable through the distortions it introduces in the lensed quasar spectra. Discrepancies in the statistics of the Lyman-$\alpha$ forest spectral absorption features can be used to reconstruct the foreground lensing potential. We extend the study of this method of Lyman-$\alpha$ forest weak gravitational lensing to lower angular forest spectrum source densities than previous work. We evaluate the performance of the Lyman-$\alpha$ lensing estimator of Metcalf et al. (2020) on mock data based on the angular forest source density ($50$ per square degree) and volume ($\sim$700,000 spectra total) of the DESI survey. We simulate the foreground galaxy distribution and lensing potentials with redshift evolution approximated by N-body simulation and simulate Gaussian-random Lyman-$\alpha$ forests to produce mock data for the entire DESI footprint. By correlating the foreground galaxy distribution with the potential reconstructed by the estimator, we find that a weak lensing detection with signal to noise of $\sim4$ will be possible with the full DESI data. We show that spectral surveys with low density and high volume are promising candidates for forest weak lensing in addition to the high resolution data that have been considered in previous work. We present forecasts for future spectral surveys and show that with larger datasets a detection with signal to noise $>10$ will be possible.

One of the hottest questions in the cosmology of self-interacting dark matter (SIDM) is whether scatterings can induce detectable core-collapse in halos by the present day. Because gravitational tides can accelerate core-collapse, the most promising targets to observe core-collapse are satellite galaxies and subhalo systems. However, simulating small subhalos is computationally intensive, especially when subhalos start to core-collapse. In this work, we present a hierarchical framework for simulating a population of SIDM subhalos, which reduces the computation time to linear order in the total number of subhalos. With this method, we simulate substructure lensing systems with multiple velocity-dependent SIDM models, and show how subhalo evolution depends on the SIDM model, subhalo mass and orbits. We find that an SIDM cross section of $\gtrsim 200$ cm$^2$/g at velocity scales relevant for subhalos' internal heat transfer is needed for a significant fraction of subhalos to core-collapse in a typical lens system at redshift $z=0.5$, and that core-collapse has unique observable features in lensing. We show quantitatively that core-collapse in subhalos is typically accelerated compared to field halos, except when the SIDM cross section is non-negligible ($\gtrsim \mathcal{O}(1)$ cm$^2$/g) at subhalos' orbital velocities, in which case evaporation by the host can delay core-collapse. This suggests that substructure lensing can be used to probe velocity-dependent SIDM models, especially if line-of-sight structures (field halos) can be distinguished from lens-plane subhalos. Intriguingly, we find that core-collapse in subhalos can explain the recently reported ultra-steep density profiles of substructures found by lensing with the \emph{Hubble Space Telescope}, Comment: 35 pages, 19 figures, comments are welcome; added subsection Results F for v2 submission; submitted to PRD

We evaluate the performance of the Lyman-$\alpha$ forest weak gravitational lensing estimator of Metcalf et al. on forest data from hydrodynamic simulations and ray-traced simulated lensing potentials. We compare the results to those obtained from the Gaussian random field simulated Ly$\alpha$ forest data and lensing potentials used in previous work. We find that the estimator is able to reconstruct the lensing potentials from the more realistic data, and investigate dependence on spectrum signal to noise. The non-linearity and non-Gaussianity in this forest data arising from gravitational instability and hydrodynamics causes a reduction in signal to noise by a factor of $\sim2.7$ for noise free data and a factor of $\sim 1.5$ for spectra with signal to noise of order unity (comparable to current observational data). Compared to Gaussian field lensing potentials, using ray-traced potentials from N-body simulations incurs a further signal to noise reduction of a factor of $\sim1.3$ at all noise levels. The non-linearity in the forest data is also observed to increase bias in the reconstructed potentials by $5-25\%$, and the ray-traced lensing potential further increases the bias by $20-30\%$. We demonstrate methods for mitigating these issues including Gaussianization and bias correction which could be used in real observations.

Strong Lensing is a powerful probe of the matter distribution in galaxies and clusters and a relevant tool for cosmography. Analyses of strong gravitational lenses with Deep Learning have become a popular approach due to these astronomical objects' rarity and image complexity. Next-generation surveys will provide more opportunities to derive science from these objects and an increasing data volume to be analyzed. However, finding strong lenses is challenging, as their number densities are orders of magnitude below those of galaxies. Therefore, specific Strong Lensing search algorithms are required to discover the highest number of systems possible with high purity and low false alarm rate. The need for better algorithms has prompted the development of an open community data science competition named Strong Gravitational Lensing Challenge (SGLC). This work presents the Deep Learning strategies and methodology used to design the highest-scoring algorithm in the II SGLC. We discuss the approach used for this dataset, the choice for a suitable architecture, particularly the use of a network with two branches to work with images in different resolutions, and its optimization. We also discuss the detectability limit, the lessons learned, and prospects for defining a tailor-made architecture in a survey in contrast to a general one. Finally, we release the models and discuss the best choice to easily adapt the model to a dataset representing a survey with a different instrument. This work helps to take a step towards efficient, adaptable and accurate analyses of strong lenses with deep learning frameworks., Comment: 14 pages, 12 figures

Forthcoming large imaging surveys such as Euclid and the Vera Rubin Observatory Legacy Survey of Space and Time are expected to find more than $10^5$ strong gravitational lens systems, including many rare and exotic populations such as compound lenses, but these $10^5$ systems will be interspersed among much larger catalogues of $\sim10^9$ galaxies. This volume of data is too much for visual inspection by volunteers alone to be feasible and gravitational lenses will only appear in a small fraction of these data which could cause a large amount of false positives. Machine learning is the obvious alternative but the algorithms' internal workings are not obviously interpretable, so their selection functions are opaque and it is not clear whether they would select against important rare populations. We design, build, and train several Convolutional Neural Networks (CNNs) to identify strong gravitational lenses using VIS, Y, J, and H bands of simulated data, with F1 scores between 0.83 and 0.91 on 100,000 test set images. We demonstrate for the first time that such CNNs do not select against compound lenses, obtaining recall scores as high as 76\% for compound arcs and 52\% for double rings. We verify this performance using Hubble Space Telescope (HST) and Hyper Suprime-Cam (HSC) data of all known compound lens systems. Finally, we explore for the first time the interpretability of these CNNs using Deep Dream, Guided Grad-CAM, and by exploring the kernels of the convolutional layers, to illuminate why CNNs succeed in compound lens selection., Comment: MNRAS accepted. 16 pages, 17 figures, The code used in this paper is publicly available at github.com/JoshWilde/LensFindery-McLensFinderFace

Strong gravitational lensing offers a compelling test of the cold dark matter paradigm, as it allows for subhaloes with masses of $\sim10^{9}$ M$_\odot$ and below to be detected. We test commonly-used techniques for detecting subhaloes superposed in images of strongly lensed galaxies. For the lens we take a simulated galaxy in a $\sim10^{13}$ M$_\odot$ halo grown in a high-resolution cosmological hydrodynamical simulation, which we view from two different directions. Though the resolution is high, we note the simulated galaxy still has an artificial core which adds additional complexity to the baryon dominated region. To remove particle noise, we represent the projected galaxy mass distribution by a series of Gaussian profiles which precisely capture the features of the projected galaxy. We first model the lens mass as a (broken) power-law density profile and then search for small haloes. Of the two projections, one has a regular elliptical shape, while the other has distinct deviations from an elliptical shape. For the former, the broken power-law model gives no false positives and correctly recovers the mass of the superposed small halo, but for the latter we find false positives and the inferred halo mass is overestimated by $\sim4-5$ times. We then use a more complex model in which the lens mass is decomposed into stellar and dark matter components. In this case, we show that we can capture the simulated galaxy's complex projected structures and correctly infer the input small halo., Comment: Accepted by MNRAS. Comments welcome!

This report is the result of a joint discussion between the Rubin and Euclid scientific communities. The work presented in this report was focused on designing and recommending an initial set of Derived Data products (DDPs) that could realize the science goals enabled by joint processing. All interested Rubin and Euclid data rights holders were invited to contribute via an online discussion forum and a series of virtual meetings. Strong interest in enhancing science with joint DDPs emerged from across a wide range of astrophysical domains: Solar System, the Galaxy, the Local Volume, from the nearby to the primaeval Universe, and cosmology., Comment: Report of the Rubin-Euclid Derived Data Products Working Group, 78 pages, 11 figures

The central dark-matter fraction of galaxies is sensitive to feedback processes during galaxy formation. Strong gravitational lensing has been effective in the precise measurement of the dark-matter fraction inside massive early-type galaxies. Here, we compare the projected dark-matter fraction of early-type galaxies inferred from the SLACS strong-lens survey, with those obtained from the EAGLE, Illustris, and IllustrisTNG hydro-dynamical simulations. Previous comparisons with some simulations revealed a large discrepancy, with considerably higher inferred dark-matter fractions -- by factors 2-3 -- inside half of the effective radius in observed strong-lens galaxies as compared to simulated galaxies. Here, we report good agreement between EAGLE and SLACS for the dark-matter fractions inside both half of the effective radius and the effective radius as a function of the galaxy's stellar mass, effective radius, and total mass-density slope. However, for IllustrisTNG and Illustris, the dark-matter fractions are lower than observed. This work consistently assumes a Chabrier IMF, which suggests that a different IMF (although not excluded) is not necessary to resolve this mismatch. The differences in the stellar feedback model between EAGLE and Illustris and IllustrisTNG, are likely the dominant cause of the difference in their dark-matter fraction, and density slope., Comment: Matches with the published version. Fixed an error in Fig 2. Updated reference. Conclusions unchanged. 7 pages, 4 figures

We investigate the structural properties, distribution and abundance of LCDM dark matter subhaloes using the Phi-4096 and Uchuu suite of N-body cosmological simulations. Thanks to the combination of their large volume, high mass resolution and superb statistics, we are able to quantify -- for the first time consistently over more than seven decades in ratio of subhalo-to-host-halo mass -- dependencies of subhalo properties with mass, maximum circular velocity, Vmax, host halo mass and distance to host halo centre. We also dissect the evolution of these dependencies over cosmic time. We provide accurate fits for the subhalo mass and velocity functions, both exhibiting decreasing power-law slopes in the expected range of values and with no significant dependence on redshift. We also find subhalo abundance to depend weakly on host halo mass. We explore the distribution of subhaloes within their hosts and its evolution over cosmic time for subhaloes located as deep as ~0.1 per cent of the host virial radius. Subhalo structural properties are codified via a concentration parameter, cV, that does not depend on any specific, pre-defined density profile and relies only on Vmax. We derive the cV-Vmax relation in the range 7-1500 km/s and find an important dependence on distance of the subhalo to the host halo centre, as already described in Molin\'e et al. (2017). Interestingly, we also find subhaloes of the same mass to be significantly more concentrated into more massive hosts. Finally, we investigate the redshift evolution of cV, and provide accurate fits that take into account all mentioned dependencies. Our results offer an unprecedented detailed characterization of the subhalo population, consistent over a wide range of subhalo and host halo masses, as well as cosmic times. Our work enables precision work in any future research involving dark matter halo substructure., Comment: 17 pages, 15 figures, 5 tables. Comments welcome!

The accuracy of photometric redshifts (photo-zs) particularly affects the results of the analyses of galaxy clustering with photometrically-selected galaxies (GCph) and weak lensing. In the next decade, space missions like Euclid will collect photometric measurements for millions of galaxies. These data should be complemented with upcoming ground-based observations to derive precise and accurate photo-zs. In this paper, we explore how the tomographic redshift binning and depth of ground-based observations will affect the cosmological constraints expected from Euclid. We focus on GCph and extend the study to include galaxy-galaxy lensing (GGL). We add a layer of complexity to the analysis by simulating several realistic photo-z distributions based on the Euclid Consortium Flagship simulation and using a machine learning photo-z algorithm. We use the Fisher matrix formalism and these galaxy samples to study the cosmological constraining power as a function of redshift binning, survey depth, and photo-z accuracy. We find that bins with equal width in redshift provide a higher Figure of Merit (FoM) than equipopulated bins and that increasing the number of redshift bins from 10 to 13 improves the FoM by 35% and 15% for GCph and its combination with GGL, respectively. For GCph, an increase of the survey depth provides a higher FoM. But the addition of faint galaxies beyond the limit of the spectroscopic training data decreases the FoM due to the spurious photo-zs. When combining both probes, the number density of the sample, which is set by the survey depth, is the main factor driving the variations in the FoM. We conclude that there is more information that can be extracted beyond the nominal 10 tomographic redshift bins of Euclid and that we should be cautious when adding faint galaxies into our sample, since they can degrade the cosmological constraints., Comment: 21 pages, 13 figures. Abstract abridged

The analysis of weak gravitational lensing in wide-field imaging surveys is considered to be a major cosmological probe of dark energy. Our capacity to constrain the dark energy equation of state relies on the accurate knowledge of the galaxy mean redshift $\langle z \rangle$. We investigate the possibility of measuring $\langle z \rangle$ with an accuracy better than $0.002\,(1+z)$, in ten tomographic bins spanning the redshift interval $0.299.8\%$. The zPDF approach could also be successful if we debias the zPDF using a spectroscopic training sample. This approach requires deep imaging data, but is weakly sensitive to spectroscopic redshift failures in the training sample. We improve the debiasing method and confirm our finding by applying it to real-world weak-lensing data sets (COSMOS and KiDS+VIKING-450)., Comment: 21 pages, 10 figures, accepted in A&A

Forthcoming large photometric surveys for cosmology require precise and accurate photometric redshift (photo-z) measurements for the success of their main science objectives. However, to date, no method has been able to produce photo-$z$s at the required accuracy using only the broad-band photometry that those surveys will provide. An assessment of the strengths and weaknesses of current methods is a crucial step in the eventual development of an approach to meet this challenge. We report on the performance of 13 photometric redshift code single value redshift estimates and redshift probability distributions (PDZs) on a common set of data, focusing particularly on the 0.2--2.6 redshift range that the Euclid mission will probe. We design a challenge using emulated Euclid data drawn from three photometric surveys of the COSMOS field. The data are divided into two samples: one calibration sample for which photometry and redshifts are provided to the participants; and the validation sample, containing only the photometry, to ensure a blinded test of the methods. Participants were invited to provide a redshift single value estimate and a PDZ for each source in the validation sample, along with a rejection flag that indicates sources they consider unfit for use in cosmological analyses. The performance of each method is assessed through a set of informative metrics, using cross-matched spectroscopic and highly-accurate photometric redshifts as the ground truth. We show that the rejection criteria set by participants are efficient in removing strong outliers, sources for which the photo-z deviates by more than 0.15(1+z) from the spectroscopic-redshift (spec-z). We also show that, while all methods are able to provide reliable single value estimates, several machine-learning methods do not manage to produce useful PDZs. [abridged], Comment: Accepted in A&A, 25 pages, 13 figures, 7 tables

Cold dark matter (CDM) constitutes most of the matter in the Universe. The interplay between dark and luminous matter in dense cosmic environments like galaxy clusters is studied theoretically using cosmological simulations. Observed gravitational lensing is used to test and characterize the properties of substructures - the small-scale distribution of dark matter - in clusters. An apt metric, the probability of strong lensing events produced by dark matter substructure, is devised and computed for 11 galaxy clusters. We report that observed cluster substructures are more efficient lenses than predicted by CDM simulations, by more than an order of magnitude. We suggest that hitherto undiagnosed systematic issues with simulations or incorrect assumptions about the properties of dark matter could explain our results., Comment: 56 pages, 15 figures. Published in Science

We introduce the Uchuu suite of large high-resolution cosmological $N$-body simulations. The largest simulation, named Uchuu, consists of 2.1 trillion ($12800^3$) dark matter particles in a box of side-length 2.0 Gpc/h, with particle mass $3.27 \times 10^{8}$ Msun/h. The highest resolution simulation, Shin-Uchuu, consists of 262 billion ($6400^3$) particles in a box of side-length 140 Mpc/h, with particle mass $8.97 \times 10^{5}$ Msun/h. Combining these simulations we can follow the evolution of dark matter halos and subhalos spanning those hosting dwarf galaxies to massive galaxy clusters across an unprecedented volume. In this first paper, we present basic statistics, dark matter power spectra, and the halo and subhalo mass functions, which demonstrate the wide dynamic range and superb statistics of the Uchuu suite. From an analysis of the evolution of the power spectra we conclude that our simulations remain accurate from the Baryon Acoustic Oscillation scale down to the very small. We also provide parameters of a mass-concentration model, which describes the evolution of halo concentration and reproduces our simulation data to within 5 per cent for halos with masses spanning nearly eight orders of magnitude at redshift 00.5, whereas no upturn is detected at z<0.5. We make publicly available various $N$-body products as part of Uchuu Data Release 1 on the Skies & Universes site. Future releases will include gravitational lensing maps and mock galaxy, X-ray cluster, and active galactic nuclei catalogues., Comment: 22 pages, 14 figures, accepted by MNRAS. We release various $N$-body products as data release 1 on http://skiesanduniverses.org/ such as subsets of simulation particles, matter power spectra, halo/subhalo catalogues, and their merger trees

The Complete Calibration of the Colour-Redshift Relation survey (C3R2) is a spectroscopic effort involving ESO and Keck facilities designed to empirically calibrate the galaxy colour-redshift relation - P(z|C) to the Euclid depth (i_AB=24.5) and is intimately linked to upcoming Stage IV dark energy missions based on weak lensing cosmology. The aim is to build a spectroscopic calibration sample that is as representative as possible of the galaxies of the Euclid weak lensing sample. In order to minimise the number of spectroscopic observations to fill the gaps in current knowledge of the P(z|C), self-organising map (SOM) representations of the galaxy colour space have been constructed. Here we present the first results of an ESO@ VLT Large Programme approved in the context of C3R2, which makes use of the two VLT optical and near-infrared multi-object spectrographs, FORS2 and KMOS. This paper focuses on high-quality spectroscopic redshifts of high-z galaxies observed with the KMOS spectrograph in the H- and K-bands. A total of 424 highly-reliable z are measured in the 1.3<=z<=2.5 range, with total success rates of 60.7% in the H-band and 32.8% in the K-band. The newly determined z fill 55% of high and 35% of lower priority empty SOM grid cells. We measured Halpha fluxes in a 1."2 radius aperture from the spectra of the spectroscopically confirmed galaxies and converted them into star formation rates. In addition, we performed an SED fitting analysis on the same sample in order to derive stellar masses, E(B-V), total magnitudes, and SFRs. We combine the results obtained from the spectra with those derived via SED fitting, and we show that the spectroscopic failures come from either weakly star-forming galaxies (at z<1.7, i.e. in the H-band) or low S/N spectra (in the K-band) of z>2 galaxies., Comment: 21 pages, 12 figures

We demonstrate a method for reconstructing the weak lensing potential from the Lyman-$\alpha$ forest data. We derive an optimal estimator for the lensing potential on the sky based on the correlation between pixels in real space. This method effectively deals with irregularly spaced data, holes in the survey, missing data and inhomogeneous noise. We demonstrate an implementation of the method with simulated spectra and weak lensing. It is shown that with a source density of $>\sim 0.5$ per square arcminutes and $\sim 200$ pixels in each spectrum ($\lambda / \Delta\lambda = 1300$) the lensing potential can be reconstructed with high fidelity if the relative absorption in the spectral pixels is signal dominated. When noise dominates the measurement of the absorption in each pixel the noise in the lensing potential is higher, but for reasonable numbers of sources and noise levels and a high fidelity map the lensing potential is obtainable. The lensing estimator could also be applied to lensing of the Cosmic Microwave Background (CMB), 21 cm intensity mapping (IM) or any case in which the correlation function of the source can be accurately estimated., Comment: 16 pages, submitted to A&A

The generation of simulated convergence maps is of key importance in fully exploiting weak lensing by Large Scale Structure (LSS) from which cosmological parameters can be derived. In this paper we present an extension of the PINOCCHIO code which produces catalogues of dark matter haloes so that it is capable of simulating weak lensing by LSS. Like WL-MOKA, the method starts with a random realisation of cosmological initial conditions, creates a halo catalogue and projects it onto the past-light-cone, and paints in haloes assuming parametric models for the mass density distribution within them. Large scale modes that are not accounted for by the haloes are constructed using linear theory. We discuss the systematic errors affecting the convergence power spectra when Lagrangian Perturbation Theory at increasing order is used to displace the haloes within PINOCCHIO, and how they depend on the grid resolution. Our approximate method is shown to be very fast when compared to full ray-tracing simulations from an N-Body run and able to recover the weak lensing signal, at different redshifts, with a few percent accuracy. It also allows for quickly constructing weak lensing covariance matrices, complementing PINOCCHIO's ability of generating the cluster mass function and galaxy clustering covariances and thus paving the way for calculating cross covariances between the different probes. This work advances these approximate methods as tools for simulating and analysing surveys data for cosmological purposes., Comment: Replaced to match the accepted version for publication in MNRAS. Added: comparison of diagonal and off-diagonal terms of the covariance matrices; cosmological constraints. Acceptance date: 2020-06-02

The combination of Galaxy-Galaxy Lensing (GGL) and Redshift Space Distortion of galaxy clustering (RSD) is a privileged technique to test General Relativity predictions, and break degeneracies between the growth rate of structure parameter $f$ and the amplitude of the linear power-spectrum $\sigma_8$. We perform a joint GGL and RSD analysis on 250 sq. degrees using shape catalogues from CFHTLenS and CFHT-Stripe 82, and spectroscopic redshifts from the BOSS CMASS sample. We adjust a model that includes non-linear biasing, RSD and Alcock-Paczynski effects. We find $f(z=0.57) =0.95\pm0.23$, $\sigma_8(z=0.57)=0.55\pm0.07$ and $\Omega_{\rm m} = 0.31\pm0.08$, in agreement with Planck cosmological results 2018. We also estimate the probe of gravity $E_{\rm G} = 0.43\pm0.10$ in agreement with $\Lambda$CDM-GR predictions of $E_{\rm G} = 0.40$. This analysis reveals that RSD efficiently decreases the GGL uncertainty on $\Omega_{\rm m}$ by a factor of 4, and by 30\% on $\sigma_8$. We use an N-body simulation supplemented by an abundance matching prescription for CMASS to build a set of overlapping lensing and clustering mocks. Together with additional spectroscopic data, this helps us to quantify and correct several systematic errors, such as photometric redshifts. We make our mock catalogues available on the Skies and Universe database., Comment: 19 pages, 14 figures, re-submitted to A&A. Mock catalogues available at http://www.skiesanduniverses.org

We use nine different galaxy formation scenarios in ten cosmological simulation boxes from the EAGLE suite of {\Lambda}CDM hydrodynamical simulations to assess the impact of feedback mechanisms in galaxy formation and compare these to observed strong gravitational lenses. To compare observations with simulations, we create strong lenses with $M_\star$ > $10^{11}$ $M_\odot$ with the appropriate resolution and noise level, and model them with an elliptical power-law mass model to constrain their total mass density slope. We also obtain the mass-size relation of the simulated lens-galaxy sample. We find significant variation in the total mass density slope at the Einstein radius and in the projected stellar mass-size relation, mainly due to different implementations of stellar and AGN feedback. We find that for lens selected galaxies, models with either too weak or too strong stellar and/or AGN feedback fail to explain the distribution of observed mass-density slopes, with the counter-intuitive trend that increasing the feedback steepens the mass density slope around the Einstein radius ($\approx$ 3-10 kpc). Models in which stellar feedback becomes inefficient at high gas densities, or weaker AGN feedback with a higher duty cycle, produce strong lenses with total mass density slopes close to isothermal (i.e. -d log({\rho})/d log(r) $\approx$ 2.0) and slope distributions statistically agreeing with observed strong lens galaxies in SLACS and BELLS. Agreement is only slightly worse with the more heterogeneous SL2S lens galaxy sample. Observations of strong-lens selected galaxies thus appear to favor models with relatively weak feedback in massive galaxies., Comment: Accepted in MNRAS

We present the UNIT $N$-body cosmological simulations project, designed to provide precise predictions for nonlinear statistics of the galaxy distribution. We focus on characterizing statistics relevant to emission line and luminous red galaxies in the current and upcoming generation of galaxy surveys. We use a suite of precise particle mesh simulations (FastPM) as well as with full $N$-body calculations with a mass resolution of $\sim 1.2\times10^9\,h^{-1}$M$_{\odot}$ to investigate the recently suggested technique of Angulo & Pontzen 2016 to suppress the variance of cosmological simulations We study redshift space distortions, cosmic voids, higher order statistics from $z=2$ down to $z=0$. We find that both two- and three-point statistics are unbiased. Over the scales of interest for baryon acoustic oscillations and redshift-space distortions, we find that the variance is greatly reduced in the two-point statistics and in the cross correlation between halos and cosmic voids, but is not reduced significantly for the three-point statistics. We demonstrate that the accuracy of the two-point correlation function for a galaxy survey with effective volume of 20 ($h^{-1}$Gpc)$^3$ is improved by about a factor of 40, indicating that two pairs of simulations with a volume of 1 ($h^{-1}$Gpc)$^3$ lead to the equivalent variance of $\sim$150 such simulations. The $N$-body simulations presented here thus provide an effective survey volume of about seven times the effective survey volume of DESI or Euclid. The data from this project, including dark matter fields, halo catalogues, and their clustering statistics, are publicly available at http://www.unitsims.org., Comment: 12 pages, 9 figures. This version matches the one accepted by MNRAS. The data from this project are publicly available at: http://www.unitsims.org

Large scale imaging surveys will increase the number of galaxy-scale strong lensing candidates by maybe three orders of magnitudes beyond the number known today. Finding these rare objects will require picking them out of at least tens of millions of images and deriving scientific results from them will require quantifying the efficiency and bias of any search method. To achieve these objectives automated methods must be developed. Because gravitational lenses are rare objects reducing false positives will be particularly important. We present a description and results of an open gravitational lens finding challenge. Participants were asked to classify 100,000 candidate objects as to whether they were gravitational lenses or not with the goal of developing better automated methods for finding lenses in large data sets. A variety of methods were used including visual inspection, arc and ring finders, support vector machines (SVM) and convolutional neural networks (CNN). We find that many of the methods will be easily fast enough to analyse the anticipated data flow. In test data, several methods are able to identify upwards of half the lenses after applying some thresholds on the lens characteristics such as lensed image brightness, size or contrast with the lens galaxy without making a single false-positive identification. This is significantly better than direct inspection by humans was able to do. (abridged), Comment: 22 pages, 16 figures, 4 tables, accepted version for A&A

We introduce simulations aimed at assessing how well weak gravitational lensing of 21cm radiation from the Epoch of Reionization ($z \sim 8$) can be measured by an SKA-like radio telescope. A simulation pipeline has been implemented to study the performance of lensing reconstruction techniques. We show how well the lensing signal can be reconstructed using the three-dimensional quadratic lensing estimator in Fourier space assuming different survey strategies. The numerical code introduced in this work is capable of dealing with issues that can not be treated analytically such as the discreteness of visibility measurements and the inclusion of a realistic model for the antennae distribution. This paves the way for future numerical studies implementing more realistic reionization models, foreground subtraction schemes, and testing the performance of lensing estimators that take into account the non-Gaussian distribution of HI after reionization. If multiple frequency channels covering $z \sim 7-11.6$ are combined, Phase 1 of SKA-Low should be able to obtain good quality images of the lensing potential with a total resolution of $\sim 1.6$ arcmin. The SKA-Low Phase 2 should be capable of providing images with high-fidelity even using data from $z\sim 7.7 - 8.3$. We perform tests aimed at evaluating the numerical implementation of the mapping reconstruction. We also discuss the possibility of measuring an accurate lensing power spectrum. Combining data from $z \sim 7-11.6$ using the SKA2-Low telescope model, we find constraints comparable to sample variance in the range $L<1000$, even for survey areas as small as $25\mbox{ deg}^2$., Comment: 23 pages, 18 figures. Accepted for pubblication in MNRAS

The flux ratios in the multiple images of gravitationally lensed quasars can provide evidence for dark matter substructure in the halo of the lensing galaxy if the flux ratios differ from those predicted by a smooth model of the lensing galaxy mass distribution. However, it is also possible that baryonic structures in the lensing galaxy, such as edge-on discs, can produce flux-ratio anomalies. In this work, we present the first statistical analysis of flux-ratio anomalies due to baryons from a numerical simulation perspective. We select galaxies with various morphological types in the Illustris simulation and ray-trace through the simulated halos, which include baryons in the main lensing galaxies but exclude any substructures, in order to explore the pure baryonic effects. Our ray-tracing results show that the baryonic components can be a major contribution to the flux-ratio anomalies in lensed quasars and that edge-on disc lenses induce the strongest anomalies. We find that the baryonic components increase the probability of finding high flux-ratio anomalies in the early-type lenses by about 8% and by about 10 - 20% in the disc lenses. The baryonic effects also induce astrometric anomalies in 13% of the mock lenses. Our results indicate that the morphology of the lens galaxy becomes important in the analysis of flux-ratio anomalies when considering the effect of baryons, and that the presence of baryons may also partially explain the discrepancy between the observed (high) anomaly frequency and what is expected due to the presence of subhalos as predicted by the CDM simulations., Comment: 16 pages, 11 figures, accepted by MNRAS

We have proposed a method for measuring weak lensing using the Lyman-alpha forest. Here we estimate the noise expected in weak lensing maps and power spectra for different sets of observational parameters. We find that surveys of the size and quality of the ones being done today and ones planned for the future will be able to measure the lensing power spectrum at a source redshift of z~2.5 with high precision and even be able to image the distribution of foreground matter with high fidelity on degree scales. For example, we predict that Lyman-alpha forest lensing measurement from the Dark Energy Spectroscopic Instrument survey should yield the mass fluctuation amplitude with statistical errors of 1.5%. By dividing the redshift range into multiple bins some tomographic lensing information should be accessible as well. This would allow for cosmological lensing measurements at higher redshift than are accessible with galaxy shear surveys and correspondingly better constraints on the evolution of dark energy at relatively early times., Comment: 8 pages, 8 figures, submitted to MNRAS

The angular positions of quasars are deflected by the gravitational lensing effect of foreground matter. The Lyman-alpha forest seen in the spectra of these quasars is therefore also lensed. We propose that the signature of weak gravitational lensing of the forest could be measured using similar techniques that have been applied to the lensed Cosmic Microwave Background, and which have also been proposed for application to spectral data from 21cm radio telescopes. As with 21cm data, the forest has the advantage of spectral information, potentially yielding many lensed "slices" at different redshifts. We perform an illustrative idealized test, generating a high resolution angular grid of quasars (of order arcminute separation), and lensing the Lyman-alphaforest spectra at redshifts z=2-3 using a foreground density field. We find that standard quadratic estimators can be used to reconstruct images of the foreground mass distribution at z~1. There currently exists a wealth of Lya forest data from quasar and galaxy spectral surveys, with smaller sightline separations expected in the future. Lyman-alpha forest lensing is sensitive to the foreground mass distribution at redshifts intermediate between CMB lensing and galaxy shear, and avoids the difficulties of shape measurement associated with the latter. With further refinement and application of mass reconstruction techniques, weak gravitational lensing of the high redshift Lya forest may become a useful new cosmological probe., Comment: 9 pages, 7 figures, submitted to MNRAS

Full ray-tracing maps of gravitational lensing, constructed from N-Body simulations, represent a fundamental tool to interpret present and future weak lensing data. However the limitation of computational resources and storage capabilities severely restrict the number of realizations that can be performed in order to accurately sample both the cosmic shear models and covariance matrices. In this paper we present a halo model formalism for weak gravitational lensing that alleviates these issues by producing weak-lensing mocks at a reduced computational cost. Our model takes as input the halo population within a desired light-cone and the linear power spectrum of the underlined cosmological model. We examine the contribution given by the presence of substructures within haloes to the cosmic shear power spectrum and quantify it to the percent level. Our method allows us to reconstruct high-resolution convergence maps, for any desired source redshifts, of light-cones that realistically trace the matter density distribution in the universe, account for masked area and sample selections. We compare our analysis on the same large scale structures constructed using ray-tracing techniques and find very good agreements both in the linear and non-linear regimes up to few percent levels. The accuracy and speed of our method demonstrate the potential of our halo model for weak lensing statistics and the possibility to generate a large sample of convergence maps for different cosmological models as needed for the analysis of large galaxy redshift surveys., Comment: 17 pages, 15 figures, accepted for publication in MNRAS

The gravitational lens SDSS J1148+1930, also known as the Cosmic Horseshoe, is one of the biggest and of the most detailed Einstein rings ever observed. We use the forward reconstruction method implemented in the lens fitting code Lensed to investigate with great detail the properties of the lens and of the background source. We model the lens with different mass distributions, focusing in particular on the determination of the slope of the dark matter component. The inherent degeneracy between the lens slope and the source size can be broken when we can isolate separate components of each lensed image, as in this case. For an elliptical power law model, $\kappa(r) \sim r^{-t}$, the results favour a flatter-than-isothermal slope with a maximum-likelihood value t = 0.08. Instead, when we consider the contribution of the baryonic matter separately, the maximum-likelihood value of the slope of the dark matter component is t = 0.31 or t = 0.44, depending on the assumed Initial Mass Function. We discuss the origin of this result by analysing in detail how the images and the sources change when the slope t changes. We also demonstrate that these slope values at the Einstein radius are not inconsistent with recent forecast from the theory of structure formation in the LambdaCDM model., Comment: 13 pages, 9 figures, accepted for publication in MNRAS

In this paper we present a large database of weak lensing light cones constructed using different snapshots from the Big MultiDark simulation (BigMDPL). The ray-tracing through different multiple planes has been performed with the GLAMER code accounting both for single source redshifts and for sources distributed along the cosmic time. This first paper presents weak lensing forecasts and results according to the geometry of the VIPERS-W1 and VIPERS-W4 field of view. Additional fields will be available on our database and new ones can be run upon request. Our database also contains some tools for lensing analysis. In this paper we present results for convergence power spectra, one point and high order weak lensing statistics useful for forecasts and for cosmological studies. Covariance matrices have also been computed for the different realisations of the W1 and W4 fields. In addition we compute also galaxy-shear and projected density contrasts for different halo masses at two lens redshifts according to the CFHTLS source redshift distribution both using stacking and cross-correlation techniques, finding very good agreement., Comment: 16 pages, 21 figures - accepted for publication in MNRAS

The Baryon Acoustic Oscillation (BAO) feature in the power spectrum of galaxies provides a standard ruler to measure the accelerated expansion of the Universe. To extract all available information about dark energy, it is necessary to measure a standard ruler in the local, z<0.2, universe where dark energy dominates most the energy density of the Universe. Though the volume available in the local universe is limited, it is just big enough to measure accurately the long 100 Mpc/h wave-mode of the BAO. Using cosmological N-body simulations and approximate methods based on Lagrangian perturbation theory, we construct a suite of a thousand light-cones to evaluate the precision at which one can measure the BAO standard ruler in the local universe. We find that using the most massive galaxies on the full sky (34,000 sq. deg.), i.e. a K(2MASS)<14 magnitude-limited sample, one can measure the BAO scale up to a precision of 4\% and 1.2\% using reconstruction). We also find that such a survey would help to detect the dynamics of dark energy.Therefore, we propose a 3-year long observational project, named the Low Redshift survey at Calar Alto (LoRCA), to observe spectroscopically about 200,000 galaxies in the northern sky to contribute to the construction of aforementioned galaxy sample. The suite of light-cones is made available to the public., Comment: 15 pages. Accepted in MNRAS. Please visit our website: http://lorca-survey.ft.uam.es/

We explore the potential of using intensity mapping surveys (MeerKAT, SKA) and optical galaxy surveys (DES, LSST) to detect HI clustering and weak gravitational lensing of 21cm emission in auto- and cross-correlation. Our forecasts show that high precision measurements of the clustering and lensing signals can be made in the near future using the intensity mapping technique. Such studies can be used to test the intensity mapping method, and constrain parameters such as the HI density $\Omega_{\rm HI}$, the HI bias $b_{\rm HI}$ and the galaxy-HI correlation coefficient $r_{\rm HI-g}$., Comment: 9 pages, 8 figures, matches version accepted for publication in MNRAS

A number of alternatives to general relativity exhibit gravitational screening in the non-linear regime of structure formation. We describe a set of algorithms that can produce weak lensing maps of large scale structure in such theories and can be used to generate mock surveys for cosmological analysis. By analysing a few basic statistics we indicate how these alternatives can be distinguished from general relativity with future weak lensing surveys., Comment: 25 pages, 7 figures, accepted by JCAP. v2: references update

The deflection, potential, shear and magnification of a gravitational lens following an elliptical power law mass model are investigated. This mass model is derived from the circular power law profile through a rescaling of the axes, similar to the case of a singular isothermal ellipsoid. The resulting deflection can be calculated explicitly and given in terms of the Gaussian hypergeometric function. Analytic expressions for the remaining lensing properties are found as well. Because the power law profile lens contains a number of well-known lens models as special cases, the equivalence of the new expressions with known results is checked. Finally, it is shown how these results naturally lead to a fast and accurate numerical scheme for computing the deflection and other lens quantities, making this method a useful tool for realistically modelling observed lenses., Comment: 6 pages, 3 figures, accepted by A&A; v2 corrects a typo in Eq. (17) and Fig. (2); sample code at https://github.com/ntessore/elliptical-power-law

Robust modelling of strong lensing systems is fundamental to exploit the information they contain about the distribution of matter in galaxies and clusters. In this work, we present Lensed, a new code which performs forward parametric modelling of strong lenses. Lensed takes advantage of a massively parallel ray-tracing kernel to perform the necessary calculations on a modern graphics processing unit (GPU). This makes the precise rendering of the background lensed sources much faster, and allows the simultaneous optimisation of tens of parameters for the selected model. With a single run, the code is able to obtain the full posterior probability distribution for the lens light, the mass distribution and the background source at the same time. Lensed is first tested on mock images which reproduce realistic space-based observations of lensing systems. In this way, we show that it is able to recover unbiased estimates of the lens parameters, even when the sources do not follow exactly the assumed model. Then, we apply it to a subsample of the SLACS lenses, in order to demonstrate its use on real data. The results generally agree with the literature, and highlight the flexibility and robustness of the algorithm., Comment: v2: major revision; accepted by MNRAS; lens reconstruction code available at http://glenco.github.io/lensed/

We perform multi-plane ray-tracing using the GLAMER gravitational lensing code within high-resolution light-cones extracted from the CoDECS simulations: a suite of cosmological runs featuring a coupling between Dark Energy and Cold Dark Matter. We show that the presence of the coupling is evident not only in the redshift evolution of the normalisation of the convergence power spectrum, but also in differences in non-linear structure formation with respect to {\Lambda}CDM. Using a tomographic approach under the assumption of a {\Lambda}CDM cosmology, we demonstrate that weak lensing measurements would result in a {\sigma}8 value that changes with the source redshift if the true underlying cosmology is a coupled Dark Energy one. This provides a generic null test for these types of models. We also find that different models of coupled Dark Energy can show either an enhanced or a suppressed correlation between convergence maps with differing source redshifts as compared to {\Lambda}CDM. This would provide a direct way to discriminate between different possible realisations of the coupled Dark Energy scenario. Finally, we discuss the impact of the coupling on several lensing observables for different source redshifts and angular scales with realistic source redshift distributions for current ground-based and future space-based lensing surveys., Comment: 17 pag. and 14 fig. replaced to match the accepted version (increased the number of light-cone realisations)

HI intensity mapping (IM) is a novel technique capable of mapping the large-scale structure of the Universe in three dimensions and delivering exquisite constraints on cosmology, by using HI as a biased tracer of the dark matter density field. This is achieved by measuring the intensity of the redshifted 21cm line over the sky in a range of redshifts without the requirement to resolve individual galaxies. In this chapter, we investigate the potential of SKA1 to deliver HI intensity maps over a broad range of frequencies and a substantial fraction of the sky. By pinning down the baryon acoustic oscillation and redshift space distortion features in the matter power spectrum -- thus determining the expansion and growth history of the Universe -- these surveys can provide powerful tests of dark energy models and modifications to General Relativity. They can also be used to probe physics on extremely large scales, where precise measurements of spatial curvature and primordial non-Gaussianity can be used to test inflation; on small scales, by measuring the sum of neutrino masses; and at high redshifts where non-standard evolution models can be probed. We discuss the impact of foregrounds as well as various instrumental and survey design parameters on the achievable constraints. In particular we analyse the feasibility of using the SKA1 autocorrelations to probe the large-scale signal., Comment: This article is part of the 'SKA Cosmology Chapter, Advancing Astrophysics with the SKA (AASKA14), Conference, Giardini Naxos (Italy), June 9th-13th 2014'

We investigate the feasibility of measuring weak gravitational lensing using 21cm intensity mapping with special emphasis on the performance of the planned Square Kilometre Array (SKA). We find that the current design for SKA-Mid should be able to measure the evolution of the lensing power spectrum at z~2-3 using this technique. This will be a probe of the expansion history of the universe and gravity at a unique range in redshift. The signal-to-noise is found to be highly dependent on evolution of the neutral hydrogen fraction in the universe with a higher HI density resulting in stronger signal. With realistic models for this, SKA Phase 1 should be capable of measuring the lensing power spectrum and its evolution. The signal-to-noise's dependence on the area and diameter of the telescope array is quantified. We further demonstrate the applications of this technique by applying it to two specific coupled dark energy models that would be difficult to observationally distinguish without information from this range of redshift. We also investigate measuring the lensing signal with 21cm emission from the Epoch of Reionization (EoR) using SKA-Low and find that it is unlikely to constrain cosmological parameters because of the small survey size, but could provide a map of the dark matter within a small region of the sky., Comment: 18 pages, 14 figures; version accepted for publication in MNRAS

We present an extension to multiple planes of the gravitational lensing code {\small GLAMER}. The method entails projecting the mass in the observed light-cone onto a discrete number of lens planes and inverse ray-shooting from the image to the source plane. The mass on each plane can be represented as halos, simulation particles, a projected mass map extracted form a numerical simulation or any combination of these. The image finding is done in a source oriented fashion, where only regions of interest are iteratively refined on an initially coarse image plane grid. The calculations are performed in parallel on shared memory machines. The code is able to handle different types of analytic halos (NFW, NSIE, power-law, etc.), haloes extracted from numerical simulations and clusters constructed from semi-analytic models ({\small MOKA}). Likewise, there are several different options for modeling the source(s) which can be distributed throughout the light-cone. The distribution of matter in the light-cone can be either taken from a pre-existing N-body numerical simulations, from halo catalogs, or are generated from an analytic mass function. We present several tests of the code and demonstrate some of its applications such as generating mock images of galaxy and galaxy cluster lenses., Comment: 14 pages, 10 figures, submitted to MNRAS

A computer code is described for the simulation of gravitational lensing data. The code incorporates adaptive mesh refinement in choosing which rays to shoot based on the requirements of the source size, location and surface brightness distribution or to find critical curves/caustics. A variety of source surface brightness models are implemented to represent galaxies and quasar emission regions. The lensing mass can be represented by point masses (stars), smoothed simulation particles, analytic halo models, pixelized mass maps or any combination of these. The deflection and beam distortions (convergence and shear) are calculated by modified tree algorithm when halos, point masses or particles are used and by FFT when mass maps are used. The combination of these methods allow for a very large dynamical range to be represented in a single simulation. Individual images of galaxies can be represented in a simulation that covers many square degrees. For an individual strongly lensed quasar, source sizes from the size of the quasar's host galaxy (~ 100 kpc) down to microlensing scales (~ 10^-4 pc) can be probed in a self consistent simulation. Descriptions of various tests of the code's accuracy are given., Comment: 13 pages, 9 figures, submitted to MNRAS, corrected some typos, replaced figure 9 after problem with numerical precision was discovered

We study how 21 cm intensity mapping can be used to measure gravitational lensing over a wide range of redshift. This can extend weak lensing measurements to higher redshifts than are accessible with conventional galaxy surveys. We construct a convergence estimator taking into account the discreteness of galaxies and calculate the expected noise level as a function of redshift and telescope parameters. At $z \sim 2-3$ we find that a telescope array with a collecting area $\sim 0.2 \, {\rm km}^2$ spread over a region with diameter $\sim 2 \, {\rm km}$ would be sufficient to measure the convergence power spectrum to high accuracy for multipoles between 10 and 1,000. We show that these measurements can be used to constrain interacting dark energy models., Comment: 5 pages, 3 figures

We study how well halo properties of galaxy clusters, like mass and concentration, are recovered using lensing data. In order to generate a large sample of systems at different redshifts we use the code MOKA. We measure halo mass and concentration using weak lensing data alone (WL), fitting to an NFW profile the reduced tangential shear profile, or by combining weak and strong lensing data, by adding information about the size of the Einstein radius (WL+SL). For different redshifts, we measure the mass and the concentration biases and find that these are mainly caused by the random orientation of the halo ellipsoid with respect to the line-of-sight. Since our simulations account for the presence of a bright central galaxy, we perform mass and concentration measurements using a generalized NFW profile which allows for a free inner slope. This reduces both the mass and the concentration biases. We discuss how the mass function and the concentration mass relation change when using WL and WL+SL estimates. We investigate how selection effects impact the measured concentration-mass relation showing that strong lens clusters may have a concentration 20-30% higher than the average, at fixed mass, considering also the particular case of strong lensing selected samples of relaxed clusters. Finally, we notice that selecting a sample of relaxed galaxy clusters, as is done in some cluster surveys, explain the concentration-mass relation biases., Comment: (1) DIFA-UniBO, (2) INAF-OABo, (3) INFN-BO, (4) JPL-Pasadena 18 pages, 19 figures - accepted for publication by MNRAS, two figures added for comparison with SGAS-SDSS and LoCuSS clusters

We study the halo mass accretion history (MAH) and its correlation with the internal structural properties in coupled dark energy cosmologies (cDE). To accurately predict all the non-linear effects caused by dark interactions, we use the COupled Dark Energy Cosmological Simulations (CoDECS). We measure the halo concentration at z=0 and the number of substructures above a mass resolution threshold for each halo. Tracing the halo merging history trees back in time, following the mass of the main halo, we develope a MAH model that accurately reproduces the halo growth in term of M_{200} in the {\Lambda}CDM Universe; we then compare the MAH in different cosmological scenarios. For cDE models with a weak constant coupling, our MAH model can reproduce the simulation results, within 10% of accuracy, by suitably rescaling the normalization of the linear matter power spectrum at z=0, {\sigma}_8. However, this is not the case for more complex scenarios, like the "bouncing" cDE model, for which the numerical analysis shows a rapid growth of haloes at high redshifts, that cannot be reproduced by simply rescaling the value of {\sigma}_8. Moreover, at fixed value of {\sigma}_8, cold dark matter (CDM) haloes in these cDE scenarios tend to be more concentrated and have a larger amount of substructures with respect to {\Lambda}CDM predictions. Finally, we present an accurate model that relates the halo concentration to the time at which it assembles half or 4% of its mass. Combining this with our MAH model, we show how halo concentrations change while varying only {\sigma}_8 in a {\Lambda}CDM Universe, at fixed halo mass., Comment: 18 pages, 14 figures, accepted for publication in MNRAS

We investigate the statistics of flux anomalies in gravitationally lensed QSOs as a function of dark matter halo properties such as substructure content and halo ellipticity. We do this by creating a very large number of simulated lenses with finite source sizes to compare with the data. After analyzing these simulations, our conclusions are: 1) The finite size of the source is important. The point source approximation commonly used can cause biased results. 2) The widely used R_cusp statistic is sensitive to halo ellipticity as well as the lens' substructure content. 3) For compact substructure, we find new upper bounds on the amount of substructure from the the fact that no simple single-galaxy lenses have been observed with a single source having more than four well separated images. 4) The frequency of image flux anomalies is largely dependent on the total surface mass density in substructures and the size--mass relation for the substructures, and not on the range of substructure masses. 5) Substructure models with the same size--mass relation produce similar numbers of flux anomalies even when their internal mass profiles are different. 6) The lack of high image multiplicity lenses puts a limit on a combination of the substructures' size--mass relation, surface density and mass. 7) Substructures with shallower mass profiles and/or larger sizes produce less extra images. 8) The constraints that we are able to measure here with current data are roughly consistent with \LambdaCDM Nbody simulations., Comment: The paper has been extensively revised for version 2 due in part to an error in the code handling the observed data. Additional simulations have been done to strengthen the conclusions which are different than in the original version. 14 pages, 11 figures, submitted to MNRAS

We present a general expression for a lognormal filter given an arbitrary nonlinear galaxy bias. We derive this filter as the maximum a posteriori solution assuming a lognormal prior distribution for the matter field with a given mean field and modeling the observed galaxy distribution by a Poissonian process. We have performed a three-dimensional implementation of this filter with a very efficient Newton-Krylov inversion scheme. Furthermore, we have tested it with a dark matter N-body simulation assuming a unit galaxy bias relation and compared the results with previous density field estimators like the inverse weighting scheme and Wiener filtering. Our results show good agreement with the underlying dark matter field for overdensities even above delta~1000 which exceeds by one order of magnitude the regime in which the lognormal is expected to be valid. The reason is that for our filter the lognormal assumption enters as a prior distribution function, but the maximum a posteriori solution is also conditioned on the data. We find that the lognormal filter is superior to the previous filtering schemes in terms of higher correlation coefficients and smaller Euclidean distances to the underlying matter field. We also show how it is able to recover the positive tail of the matter density field distribution for a unit bias relation down to scales of about >~2 Mpc/h., Comment: 17 pages, 9 figures, 1 table

We present the largest Wiener reconstruction of the cosmic density field made to date. The reconstruction is based on the Sloan Digital Sky Survey data release 6 covering the northern Galactic cap. We use a novel supersampling algorithm to suppress aliasing effects and a Krylov-space inversion method to enable high performance with high resolution. These techniques are implemented in the ARGO computer code. We reconstruct the field over a 500 Mpc cube with Mpc grid-resolution while accounting both for the angular and radial selection functions of the SDSS, and the shot noise giving an effective resolution of the order of ~10 Mpc. In addition, we correct for the redshift distortions in the linear and nonlinear regimes in an approximate way. We show that the commonly used method of inverse weighting the galaxies by the corresponding selection function heads to excess noise in regions where the density of the observed galaxies is small. It is more accurate and conservative to adopt a Bayesian framework in which we model the galaxy selection/detection process to be Poisson-binomial. This results in heavier smoothing in regions of reduced sampling density. Our results show a complex cosmic web structure with huge void regions indicating that the recovered matter distribution is highly non-Gaussian. Filamentary structures are clearly visible on scales up to ~20 Mpc. We also calculate the statistical distribution of density after smoothing the reconstruction with Gaussian kernels of different radii r_S and find good agreement with a log-normal distribution for ~10 Mpc < r_S < ~30 Mpc., Comment: 24 pages, 12 figures, 2 tables

We study the constraints which the next generation of radio telescopes could place on the mass and number of neutrino species by studying the gravitational lensing of high redshift 21 cm emission in combination with wide-angle surveys of galaxy lensing. We use simple characterizations of reionization history and of proposed telescope designs to forecast the constraints and detectability threshold for neutrinos. It is found that the degeneracy between neutrino parameters and dark energy parameters is significantly reduced by incorporating 21 cm lensing. The combination of galaxy and 21 cm lensing could constrain the sum of the neutrino masses to within ~ 0.04 eV and the number of species to within ~ 0.1. This is an improvement of a factor of 2.6 in mass and 1.3 in number over a galaxy lensing survey alone. This includes marginalizing over an 11 parameter cosmological model with a two parameter model for the dark energy equation of state. If the dark energy equation of state is held fixed at w = p/\rho=-1 the constraints improve to ~0.03 eV and 0.04. These forecasted errors depend critically on the fraction of sky that can be surveyed in redshifted 21 cm emission (25% is assumed here) and the redshift of reionization ($z=7$ is assumed here). It is also found that neutrinos with masses too small to be detected in the data could none the less cause a significant bias in the measured dark energy equation of state., Comment: 7 pages, 6 figures, submitted to MNRAS

(abridged) The Observatory for Multi-Epoch Gravitational Lens Astrophysics (OMEGA) is a mission concept for a 1.5-m near-UV through near-IR space observatory that will be dedicated to frequent imaging and spectroscopic monitoring of ~100 multiply-imaged active galactic nuclei over the whole sky. Using wavelength-tailored dichroics with extremely high transmittance, efficient imaging in six channels will be done simultaneously during each visit to each target. The separate spectroscopic mode, engaged through a flip-in mirror, uses an image slicer spectrograph. After a period of many visits to all targets, the resulting multidimensional movies can then be analyzed to a) measure the mass function of dark matter substructure; b) measure precise masses of the accreting black holes as well as the structure of their accretion disks and their environments over several decades of physical scale; and c) measure a combination of the local Hubble expansion and cosmological distances to unprecedented precision., Comment: Proceedings paper for the SPIE Astronomical Telescopes and Instrumentation 2008

Low-frequency radio observations of neutral hydrogen during and before the epoch of cosmic reionization will provide hundreds of quasi-independent source planes, each of precisely known redshift, if a resolution of ~ 1 arcminutes or better can be attained. These planes can be used to reconstruct the projected mass distribution of foreground material. A wide-area survey of 21 cm lensing would provide very sensitive constraints on cosmological parameters, in particular on dark energy. These are up to 20 times tighter than the constraints obtainable from comparably sized, very deep surveys of galaxy lensing although the best constraints come from combining data of the two types. Any radio telescope capable of mapping the 21cm brightness temperature with good frequency resolution (~ 0.05 MHz) over a band of width ~> 10 MHz should be able to make mass maps of high quality. If the reionization epoch is at z ~ 9 very large amounts of cosmological information will be accessible. The planned Square Kilometer Array (SKA) should be capable of mapping the mass with a resolution of a few arcminutes depending on the reionization history of the universe and how successfully foreground sources can be subtracted. The Low-Frequency Array (LOFAR) will be able to measure an accurate matter power spectrum if the same conditions are met., Comment: prize wining contribution to proceedings of the Cosmology 2007 conference in Venice, 4 pages, one color figure

We study the constraints which the next generation of radio telescopes could place on the nature of dark energy, dark matter and inflation by studying the gravitational lensing of high redshift 21 cm emission, and we compare with the constraints obtainable from wide-angle surveys of galaxy lensing. If the reionization epoch is effectively at z ~ 8 or later, very large amounts of cosmological information will be accessible to telescopes like SKA and LOFAR. We use simple characterizations of reionization history and of proposed telescope designs to investigate how well the two-dimensional convergence power spectrum, the three-dimensional matter power spectrum, the evolution of the linear growth function, and the standard cosmological parameters can be measured from radio data. The power spectra can be measured accurately over a wide range of wavenumbers at z ~ 2, and the evolution in the cosmic energy density can be probed from z ~ 0.5 to z ~ 7. This results in a characterization of the shape of the power spectra (i.e. of the nature of dark matter and of inflationary structure generation) which is potentially more precise than that obtained from galaxy lensing surveys. On the other hand, the dark energy parameters in their conventional parametrization (Omega_Lambda, w_o, w_a) are somewhat less well constrained by feasible 21 cm lensing surveys than by an all-sky galaxy lensing survey although a 21 cm surveys might be more powerful than galaxy surveys for constraining models with "early" dark energy. Overall, the best constraints come from combining surveys of the two types. This results in extremely tight constraints on dark matter and inflation, and improves constraints on dark energy, as judged by the standard figure of merit, by more than an order of magnitude over either survey alone., Comment: submitted to MNRAS, 12 pages, error in computer code corrected which changed constraints on some cosmological parameters, change to lensing estimator to improve performance

21-cm emission from neutral hydrogen during and before the epoch of cosmic reionisation is gravitationally lensed by material at all lower redshifts. Low-frequency radio observations of this emission can be used to reconstruct the projected mass distribution of foreground material, both light and dark. We compare the potential imaging capabilities of such 21-cm lensing with those of future galaxy lensing surveys. We use the Millennium Simulation to simulate large-area maps of the lensing convergence with the noise, resolution and redshift-weighting achievable with a variety of idealised observation programmes. We find that the signal-to-noise of 21-cm lens maps can far exceed that of any map made using galaxy lensing. If the irreducible noise limit can be reached with a sufficiently large radio telescope, the projected convergence map provides a high-fidelity image of the true matter distribution, allowing the dark matter halos of individual galaxies to be viewed directly, and giving a wealth of statistical and morphological information about the relative distributions of mass and light. For instrumental designs like that planned for the Square Kilometer Array (SKA), high-fidelity mass imaging may be possible near the resolution limit of the core array of the telescope., Comment: version accepted for publication in MNRAS (reduced-resolution figures)

We use the distribution, and particularly the skewness, of high redshift type Ia supernovae brightnesses relative to the low redshift sample to constrain the density of macroscopic compact objects (MCOs) in the universe. The data favors dark matter made of microscopic particles (such as the LSP) at 89% confidence. Future data will greatly improve this limit. This constraint is valid for a range in MCO mass from 10^-2 Msun to 10^10 Msun. Combined with other constraints, MCOs larger than one tenth the mass of Earth (~ 10^-7 Msun) can be eliminated as the sole constituent of dark matter., Comment: 4 pages, 1 figure