Investigating the origins of the CMB-XRB cross correlation

Recently, we presented evidence for a cross-correlation of the WMAP satellite map of the cosmic microwave background (CMB) and the HEAO1 satellite map of the hard X-ray background (XRB) with a dimensionless amplitude of 0.14 +- 0.05 normalized to the product of the rms fluctuations of the CMB and XRB (Boughn & Crittenden, 2004). Such a correlation is expected in a universe dominated by a cosmological constant via the integrated Sachs-Wolfe (ISW) effect and the level of the correlation observed is consistent with that predicted by the currently favored Lambda cold dark matter model of the universe. Since this offers independent confirmation of the cosmological model, it is important to verify the origin of the correlation. Here we explore in detail some possible foreground sources of the correlation. The present evidence all supports an ISW origin.Comment: 8 pages, 7 eps figure

Cell count moments in the halo model

We study cell count moments up to fifth order of the distributions of haloes, of halo substructures as a proxy for galaxies, and of mass in the context of the halo model and compare theoretical predictions to the results of numerical simulations. On scales larger than the size of the largest cluster, we present a simple point cluster model in which results depend only on cluster-cluster correlations and on the distribution of the number of objects within a cluster, or cluster occupancy. The point cluster model leads to expressions for moments of galaxy counts in which the volume-averaged moments on large scales approach those of the halo distribution and on smaller scales exhibit hierarchical clustering with amplitudes Sk determined by moments of the occupancy distribution. In this limit, the halo model predictions are purely combinatoric, and have no dependence on halo profile, concentration parameter or potential asphericity. The full halo model introduces only two additional effects: on large scales, haloes of different mass have different clustering strengths, introducing relative bias parameters; and on the smallest scales, halo structure is resolved and details of the halo profile become important, introducing shape-dependent form factors. Because of differences between discrete and continuous statistics, the hierarchical amplitudes for galaxies and for mass behave differently on small scales even if galaxy number is exactly proportional to mass, a difference that is not necessarily well described in terms of bia

An accurate tool for the fast generation of dark matter halo catalogues

We present a new parallel implementation of the PINpointing Orbit Crossing-Collapsed HIerarchical Objects (PINOCCHIO) algorithm, a quick tool, based on Lagrangian Perturbation Theory, for the hierarchical build-up of dark matter (DM) haloes in cosmological volumes. To assess its ability to predict halo correlations on large scales, we compare its results with those of an N-body simulation of a 3 h−1 Gpc box sampled with 20483 particles taken from the MICE suite, matching the same seeds for the initial conditions. Thanks to the Fastest Fourier Transforms in the West (FFTW) libraries and to the relatively simple design, the code shows very good scaling properties. The CPU time required by PINOCCHIO is a tiny fraction (∼1/2000) of that required by the MICE simulation. Varying some of PINOCCHIO numerical parameters allows one to produce a universal mass function that lies in the range allowed by published fits, although it underestimates the MICE mass function of Friends-of-Friends (FoF) haloes in the high-mass tail. We compare the matter–halo and the halo–halo power spectra with those of the MICE simulation and find that these two-point statistics are well recovered on large scales. In particular, when catalogues are matched in number density, agreement within 10 per cent is achieved for the halo power spectrum. At scales k > 0.1 h Mpc−1, the inaccuracy of the Zel’dovich approximation in locating halo positions causes an underestimate of the power spectrum that can be modelled as a Gaussian factor with a damping scale of d = 3 h−1 Mpc at z = 0, decreasing at higher redshift. Finally, a remarkable match is obtained for the reduced halo bispectrum, showing a good description of non-linear halo bias. Our results demonstrate the potential of PINOCCHIO as an accurate and flexible tool for generating large ensembles of mock galaxy surveys, with interesting applications for the analysis of large galaxy redshift surveys

Statistical Properties of Galactic Starlight Polarization

We present a statistical analysis of Galactic interstellar polarization from the largest compilation available of starlight data. The data comprises ~ 9300 stars of which we have selected ~ 5500 for our analysis. We find a nearly linear growth of mean polarization degree with extinction. The amplitude of this correlation shows that interstellar grains are not fully aligned with the Galactic magnetic field, which can be interpreted as the effect of a large random component of the field. In agreement with earlier studies of more limited scope, we estimate the ratio of the uniform to the random plane-of-the-sky components of the magnetic field to be B_u/B_r = 0.8. Moreover, a clear correlation exists between polarization degree and polarization angle what provides evidence that the magnetic field geometry follows Galactic structures on large-scales. The angular power spectrum C_l of the starlight polarization degree for Galactic plane data (|b| < 10 deg) is consistent with a power-law, C_l ~ l^{-1.5} (where l ~ 180 deg/\theta is the multipole order), for all angular scales \theta > 10 arcmin. An investigation of sparse and inhomogeneous sampling of the data shows that the starlight data analyzed traces an underlying polarized continuum that has the same power spectrum slope, C_l ~ l^{-1.5}. Our findings suggest that starlight data can be safely used for the modeling of Galactic polarized continuum emission at other wavelengths.Comment: 31 pages, 11 figures. Minor corrections and some clarifications included. Matches version accepted for publication by the Astrophysical Journa

Photometric Selection of Emission Line Galaxies, Clustering Analysis and a Search for the ISW effect

We investigate the use of simple colour cuts applied to the SDSS optical imaging to perform photometric selections of emission line galaxies out to z<1. From colour-cuts using the SDSS g, r and i bands, we obtain mean photometric redshifts of z=0.32+-0.08, z=0.44+-0.12 and z=0.65+-0.21. We further calibrate our high redshift selection using spectroscopic observations with the AAOmega spectrograph on the 4m Anglo-Australian Telescope (AAT), observing ~50-200 galaxy candidates in 4 separate fields. With just 1-hour of integration time and with seeing of ~1.6", we successfully determined redshifts for ~65% of the targeted candidates. We calculate the angular correlation functions of the samples and find correlation lengths of r0=2.64 h-1 Mpc, r0=3.62 h-1 Mpc and r0=5.88 h-1 Mpc for the low, mid and high redshift samples respectively. Comparing these results with predicted dark matter clustering, we estimate the bias parameter for each sample to be b=0.70, b=0.92 and b=1.46. We calculate the 2-point redshift-space correlation function at z~0.6 and find a clustering amplitude of s0=6.4 h-1 Mpc. Finally, we use our photometric sample to search for the Integrated Sachs-Wolfe signal in the WMAP 5yr data. We cross-correlate our three redshift samples with the WMAP W, V, Q and K bands and find an overall trend for a positive signal similar to that expected from models. However, the signal in each is relatively weak. Combining all three galaxy samples we find a signal of wTg(<100')=0.20+-0.12 microK in the WMAP W-band, a significance of 1.7sigma.Comment: 14 pages, 17 figures, submitted to MNRA

Ray-tracing through the Millennium Simulation: Born corrections and lens-lens coupling in cosmic shear and galaxy-galaxy lensing

(abridged) We study the accuracy of various approximations to cosmic shear and weak galaxy-galaxy lensing and investigate effects of Born corrections and lens-lens coupling. We use ray-tracing through the Millennium Simulation to calculate various cosmic-shear and galaxy-galaxy-lensing statistics. We compare the results from ray-tracing to semi-analytic predictions. We find: (i) The linear approximation provides an excellent fit to cosmic-shear power spectra as long as the actual matter power spectrum is used as input. Common fitting formulae, however, strongly underestimate the cosmic-shear power spectra. Halo models provide a better fit to cosmic shear-power spectra, but there are still noticeable deviations. (ii) Cosmic-shear B-modes induced by Born corrections and lens-lens coupling are at least three orders of magnitude smaller than cosmic-shear E-modes. Semi-analytic extensions to the linear approximation predict the right order of magnitude for the B-mode. Compared to the ray-tracing results, however, the semi-analytic predictions may differ by a factor two on small scales and also show a different scale dependence. (iii) The linear approximation may under- or overestimate the galaxy-galaxy-lensing shear signal by several percent due to the neglect of magnification bias, which may lead to a correlation between the shear and the observed number density of lenses. We conclude: (i) Current semi-analytic models need to be improved in order to match the degree of statistical accuracy expected for future weak-lensing surveys. (ii) Shear B-modes induced by corrections to the linear approximation are not important for future cosmic-shear surveys. (iii) Magnification bias can be important for galaxy-galaxy-lensing surveys.Comment: version taking comments into accoun

Dark energy survey year 3 results: Galaxy sample for BAO measurement

Rosell, A., et al. (DES Collaboration)In this paper, we present and validate the galaxy sample used for the analysis of the baryon acoustic oscillation (BAO) signal in the Dark Energy Survey (DES) Y3 data. The definition is based on a colour and redshift-dependent magnitude cut optimized to select galaxies at redshifts higher than 0.5, while ensuring a high-quality determination. The sample covers ~4100 deg2 to a depth of i = 22.3 (AB) at 10s. It contains 7031 993 galaxies in the redshift range from z = 0.6 to 1.1, with a mean effective redshift of 0.835. Redshifts are estimated with the machine learning algorithm DNF, and are validated using the VIPERS PDR2 sample. We find a mean redshift bias of zbias~0.01 and a mean uncertainty, in units of 1 + z, of σ68~0.03. We evaluate the galaxy population of the sample, showing it is mostly built upon Elliptical to Sbc types. Furthermore, we find a low level of stellar contamination of ≤ 4 per cent. We present the method used to mitigate the effect of spurious clustering coming from observing conditions and other large-scale systematics.We apply it to the BAO sample and calculate weights that are used to get a robust estimate of the galaxy clustering signal. This paper is one of a series dedicated to the analysis of the BAO signal in DES Y3. In the companion papers, we present the galaxy mock catalogues used to calibrate the analysis and the angular diameter distance constraints obtained through the fitting to the BAO scale.The DES data management system is supported by the National Science Foundation under Grant Numbers AST-1138766 and AST-1536171. The DES participants from Spanish institutions are partially supported by MICINN under grants ESP2017-89838,PGC2018-094773, PGC2018-102021, SEV-2016-0588, SEV-2016-0597, and MDM-2015-0509, some of which include ERDF funds from the European Union. IFAE is partially funded by the CERCA program of the Generalitat de Catalunya. Research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Program (FP7/2007-2013) including ERC grant agreements 240672, 291329, and 306478. We acknowledge support from the Brazilian Instituto Nacional de Ciência e Tecnologia (INCT) do e-Universo (CNPq grant 465376/2014-2). ACR acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under grant AYA2017-84061-P, co-financed by FEDER (European Regional Development Funds) and by the Spanish Space Research Program ‘Participation in the NISP instrument and preparation for the science of EUCLID’ (ESP2017-84272-C2-1-R). SA was supported by the MICUES project, funded by the EU’s H2020 MSCA grant agreement no. 713366 (InterTalentum UAM)

First Detection of Polarization of the Submillimetre Diffuse Galactic Dust Emission by Archeops

We present the first determination of the Galactic polarized emission at 353 GHz by Archeops. The data were taken during the Arctic night of February 7, 2002 after the balloon--borne instrument was launched by CNES from the Swedish Esrange base near Kiruna. In addition to the 143 GHz and 217 GHz frequency bands dedicated to CMB studies, Archeops had one 545 GHz and six 353 GHz bolometers mounted in three polarization sensitive pairs that were used for Galactic foreground studies. We present maps of the I, Q, U Stokes parameters over 17% of the sky and with a 13 arcmin resolution at 353 GHz (850 microns). They show a significant Galactic large scale polarized emission coherent on the longitude ranges [100, 120] and [180, 200] deg. with a degree of polarization at the level of 4-5%, in agreement with expectations from starlight polarization measurements. Some regions in the Galactic plane (Gem OB1, Cassiopeia) show an even stronger degree of polarization in the range 10-20%. Those findings provide strong evidence for a powerful grain alignment mechanism throughout the interstellar medium and a coherent magnetic field coplanar to the Galactic plane. This magnetic field pervades even some dense clouds. Extrapolated to high Galactic latitude, these results indicate that interstellar dust polarized emission is the major foreground for PLANCK-HFI CMB polarization measurement.Comment: Submitted to Astron. & Astrophys., 14 pages, 12 Fig., 2 Table

Benchmark Parameters for CMB Polarization Experiments

The recently detected polarization of the cosmic microwave background (CMB) holds the potential for revealing the physics of inflation and gravitationally mapping the large-scale structure of the universe, if so called B-mode signals below 10^{-7}, or tenths of a uK, can be reliably detected. We provide a language for describing systematic effects which distort the observed CMB temperature and polarization fields and so contaminate the B-modes. We identify 7 types of effects, described by 11 distortion fields, and show their association with known instrumental systematics such as common mode and differential gain fluctuations, line cross-coupling, pointing errors, and differential polarized beam effects. Because of aliasing from the small-scale structure in the CMB, even uncorrelated fluctuations in these effects can affect the large-scale B modes relevant to gravitational waves. Many of these problems are greatly reduced by having an instrumental beam that resolves the primary anisotropies (FWHM << 10'). To reach the ultimate goal of an inflationary energy scale of 3 \times 10^{15} GeV, polarization distortion fluctuations must be controlled at the 10^{-2}-10^{-3} level and temperature leakage to the 10^{-4}-10^{-3} level depending on effect. For example pointing errors must be controlled to 1.5'' rms for arcminute scale beams or a percent of the Gaussian beam width for larger beams; low spatial frequency differential gain fluctuations or line cross-coupling must be eliminated at the level of 10^{-4} rms.Comment: 11 pages, 5 figures, submitted to PR