Mapping dark matter in the gamma-ray sky with galaxy catalogs

Cross-correlating gamma-ray maps with locations of galaxies in the low-redshift Universe vastly increases sensitivity to signatures of annihilation of dark matter particles. Low-redshift galaxies are ideal targets, as the largest contribution to anisotropy in the gamma-ray sky from annihilation comes from $z\lesssim 0.1$, where we expect minimal contributions from astrophysical sources such as blazars. Cross-correlating the five-year data of Fermi-LAT with the redshift catalog of the 2MASS survey can detect gamma rays from annihilation if dark matter has the canonical annihilation cross section and its mass is smaller than $\sim$100 GeV.Comment: 7 pages, 4 figures; accepted for publication in Physical Review

Angular power spectrum of galaxies in the 2MASS Redshift Survey

We present the measurement and interpretation of the angular power spectrum of nearby galaxies in the 2MASS Redshift Survey catalog with spectroscopic redshifts up to $z\approx 0.1$. We detect the angular power spectrum up to a multipole of $\ell\approx 1000$. We find that the measured power spectrum is dominated by galaxies living inside nearby galaxy clusters and groups. We use the halo occupation distribution (HOD) formalism to model the power spectrum, obtaining a fit with reasonable parameters. These HOD parameters are in agreement with the 2MASS galaxy distribution we measure toward the known nearby galaxy clusters, confirming validity of our analysis.Comment: 8 pages, 6 figure

The cosmic microwave background Cold Spot anomaly: the impact of sky masking and the expected contribution from the Integrated Sachs-Wolfe effect

We re-analyse the cosmic microwave background (CMB) Cold Spot (CS) anomaly with particular focus on understanding the bias a mask (contaminated by Galactic and point sources) may introduce. We measure the coldest spot, found by applying the Spherical Mexican Hat Wavelet transform on 100 000 cut-sky (masked) and full-sky CMB simulated maps. The CS itself is barely affected by the mask; we estimate a 94 per cent probability that the CS is the full-sky temperature minimum. However, approximately 48 per cent (masked fraction of the mask) of full-sky minima are obscured by the mask. Since the observed minima are slightly hotter than the full-sky ensemble of minima, a cut-sky analysis would have found the CS to be significant at approximately 2.2 sigma with a wavelet angular scale of R = 5 degrees. None the less, comparisons to full-sky minima show the CS significance to be only approximately 1.9 sigma and less than 2 sigma for all R. The CS on the last scattering surface may be hotter due to the integrated Sachs-Wolfe effect in the line of sight. However, our simulations show that this on average only approximately 10 per cent (about 10 micro K but consistent with zero) of the CS temperature profile. This is consistent with Lambda and cold dark matter reconstructions of this effect based on observed line-of-sight voids.Comment: 6 pages, 5 figures, changes made to match version published in MNRA

Could multiple voids explain the Cosmic Microwave Background Cold Spot anomaly?

Understanding the observed Cold Spot (CS) (temperature of ~ -150 mu K at its centre) on the Cosmic Microwave Background (CMB) is an outstanding problem. Explanations vary from assuming it is just a > 3 sigma primordial Gaussian fluctuation to the imprint of a supervoid via the Integrated Sachs-Wolfe and Rees-Sciama (ISW+RS) effects. Since single spherical supervoids cannot account for the full profile, the ISW+RS of multiple line-of-sight voids is studied here to mimic the structure of the cosmic web. Two structure configurations are considered. The first, through simulations of 20 voids, produces a central mean temperature of ~-50 mu K. In this model the central CS temperature lies at ~ 2 sigma but fails to explain the CS hot ring. An alternative multi-void model (using more pronounced compensated voids) produces much smaller temperature profiles, but contains a prominent hot ring. Arrangements containing closely placed voids at low redshift are found to be particularly well suited to produce CS-like profiles. We then measure the significance of the CS if CS-like profiles (which are fitted to the ISW+RS of multi-void scenarios) are removed. The CS tension with the LCDM model can be reduced dramatically for an array of temperature profiles smaller than the CS itself.Comment: 5 pages, 3 figures, as appears in MNRAS Letter

Cross correlation surveys with the Square Kilometre Array

By the time that the first phase of the Square Kilometre Array is deployed it will be able to perform state of the art Large Scale Structure (LSS) as well as Weak Gravitational Lensing (WGL) measurements of the distribution of matter in the Universe. In this chapter we concentrate on the synergies that result from cross-correlating these different SKA data products as well as external correlation with the weak lensing measurements available from CMB missions. We show that the Dark Energy figures of merit obtained individually from WGL/LSS measurements and their independent combination is significantly increased when their full cross-correlations are taken into account. This is due to the increased knowledge of galaxy bias as a function of redshift as well as the extra information from the different cosmological dependences of the cross-correlations. We show that the cross-correlation between a spectroscopic LSS sample and a weak lensing sample with photometric redshifts can calibrate these same photometric redshifts, and their scatter, to high accuracy by modelling them as nuisance parameters and fitting them simultaneously cosmology. Finally we show that Modified Gravity parameters are greatly constrained by this cross-correlations because weak lensing and redshift space distortions (from the LSS survey) break strong degeneracies in common parameterisations of modified gravity.Comment: 12 pages, 3 figures. This article is part of the 'Cosmology Chapter, Advancing Astrophysics with the SKA (AASKA14) Conference, Giardini Naxos (Italy), June 9th-13th 2014

Estimating the large-scale angular power spectrum in the presence of systematics: a case study of Sloan Digital Sky Survey quasars

The angular power spectrum is a powerful statistic for analysing cosmological signals imprinted in the clustering of matter. However, current galaxy and quasar surveys cover limited portions of the sky, and are contaminated by systematics that can mimic cosmological signatures and jeopardise the interpretation of the measured power spectra. We provide a framework for obtaining unbiased estimates of the angular power spectra of large-scale structure surveys at the largest scales using quadratic estimators. The method is tested by analysing the 600 CMASS mock catalogues constructed by Manera et al. (2013) for the Baryon Oscillation Spectroscopic Survey (BOSS). We then consider the Richards et al. (2009) catalogue of photometric quasars from the Sixth Data Release (DR6) of the Sloan Digital Sky Survey (SDSS), which is known to include significant stellar contamination and systematic uncertainties. Focusing on the sample of ultraviolet-excess (UVX) sources, we show that the excess clustering power present on the largest-scales can be largely mitigated by making use of improved sky masks and projecting out the modes corresponding to the principal systematics. In particular, we find that the sample of objects with photometric redshift $1.3 < z_p < 2.2$ exhibits no evidence of contamination when using our most conservative mask and mode projection. This indicates that any residual systematics are well within the statistical uncertainties. We conclude that, using our approach, this sample can be used for cosmological studies.Comment: 18 pages, 18 figures. Version accepted by MNRA

Full-sky CMB lensing reconstruction in presence of sky-cuts

We consider the reconstruction of the CMB lensing potential and its power spectrum of the full sphere in presence of sky-cuts due to point sources and Galactic contaminations. Those two effects are treated separately. Small regions contaminated by point sources are filled in using Gaussian constrained realizations. The Galactic plane is simply masked using an apodized mask before lensing reconstruction. This algorithm recovers the power spectrum of the lensing potential with no significant bias.Comment: Submitted to A&