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Sanchez-Conde M.A.,Kavli Institute for Particle Astrophysics and Cosmology | Prada F.,Campus of International Excellence UAMCSIC | Prada F.,Autonomous University of Madrid | Prada F.,Institute Astrofisica Of Andalucia Iaa Csic
Monthly Notices of the Royal Astronomical Society | Year: 2014

In the standard cold dark matter (CDM) theory for understanding the formation of structure in theUniverse, there exists a tight connection between the properties of darkmatter (DM) haloes, and their formation epochs. Such relation can be expressed in terms of a single key parameter, namely the halo concentration. In this work, we examine the median concentration-mass relation, c(M), at present time, over more than 20 orders of magnitude in halo mass, i.e. from tiny Earth-mass microhaloes up to galaxy clusters. The c(M) model proposed by Prada et al. (2012), which links the halo concentration with the rms amplitude of matter linear fluctuations, describes remarkably well all the available N-body simulation data down to ~10-6 h -1M( microhaloes. A clear fattening of the halo concentration-mass relation towards smaller masses is observed, that excludes the commonly adopted power-law c(M) models, and stands as a natural prediction for the CDM paradigm. We provide a parametrization for the c(M) relation that works accurately for all halo masses. This feature in the c(M) relation at low masses has decisive consequences e.g. for γ -ray DM searches, as it implies more modest boosts of the DM annihilation flux due to substructure, i.e. ~35 for galaxy clusters and ~15 for galaxies like our own, as compared to those huge values adopted in the literature that rely on such power-law c(M) extrapolations. We provide a parametrization of the boosts that can be safely used for dwarfs to galaxy cluster-size haloes. © 2014 The Authors. Source

Dominguez A.,University of California at Riverside | Prada F.,Campus of International Excellence UAMCSIC | Prada F.,Autonomous University of Madrid | Prada F.,Institute Astrofisica Of Andalucia Csic
Astrophysical Journal Letters | Year: 2013

A measurement of the expansion rate of the universe (that is, the Hubble constant, H 0) is derived here using the γ-ray attenuation observed in the spectra of γ-ray sources produced by the interaction of extragalactic γ-ray photons with the photons of the extragalactic background light (EBL). The Hubble constant determined with our technique, for a ΛCDM cosmology, is km s-1 Mpc-1. This value is compatible with present-day measurements using well-established methods such as local distance ladders and cosmological probes. The recent detection of the cosmic γ-ray horizon (CGRH) from multiwavelength observations of blazars, together with the advances in the knowledge of the EBL, allow us to measure the expansion rate of the universe. This estimate of the Hubble constant shows that γ-ray astronomy has reached a mature enough state to provide cosmological measurements, which may become more competitive in the future with the construction of the Cherenkov Telescope Array. We find that the maximum dependence of the CGRH on the Hubble constant is approximately between redshifts 0.04 and 0.1, thus this is a smoking gun for planning future observational efforts. Other cosmological parameters, such as the total dark matter density Ωm and the dark energy equation of state w, are explored as well. © 2013. The American Astronomical Society. All rights reserved. Source

Nuza S.E.,Leibniz Institute for Astrophysics Potsdam | Sanchez A.G.,Max Planck Insitut fur Extraterrestrische Physik | Prada F.,Campus of International Excellence UAMCSIC | Prada F.,Autonomous University of Madrid | And 31 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present results on the clustering of 282 068 galaxies in theBaryon Oscillation Spectroscopic Survey (BOSS) sample of massive galaxies with redshifts 0.4 < z < 0.7 which is part of the Sloan Digital Sky Survey III project. Our results cover a large range of scales from ∼500 to ∼90 h-1 Mpc. We compare these estimates with the expectations of the flat A cold dark matter (ACDM) standard cosmological model with parameters compatible with Wilkinson Microwave Anisotropy Probe 7 data. We use the MultiDark cosmological simulation, one of the largest N-body runs presently available, together with a simple halo abundance matching technique, to estimate galaxy correlation functions, power spectra, abundance of subhaloes and galaxy biases. We find that the ACDM model gives a reasonable description to the observed correlation functions at z ≈ 0.5, which is remarkably good agreement considering that the model, once matched to the observed abundance of BOSS galaxies, does not have any free parameters. However, we find a ≥10 per cent deviation in the correlation functions for scales ≤ 1 and ∼10-40 h-1 Mpc. A more realistic abundance matching model and better statistics from upcoming observations are needed to clarify the situation. We also estimate that about 12 per cent of the 'galaxies' in the abundance-matched sample are satellites inhabiting central haloes with mass M ≥ 1014 h-1 M⊙. Using the MultiDark simulation, we also study the real-space halo bias b of the matched catalogue finding that b = 2.00 ± 0.07 at large scales, consistent with the one obtained using the measured BOSS-projected correlation function. Furthermore, the linear large-scale bias, defined using the extrapolated linear matter power spectrum, depends on the number density n of the abundance-matched sample as b=-0.048- (0.594 ± 0.02)log10(n/ h3 Mpc-3). Extrapolating these results to baryon acoustic oscillation scales, we measure a scale-dependent damping of the acoustic signal produced by non-linear evolution that leads to ∼2-4 per cent dips at ≥ 3s level for wavenumbers k ≥ 0.1 h Mpc-1 in the linear large-scale bias. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Hernandez-Monteagudo C.,Max Planck Institute for Astrophysics | Ross A.J.,University of Portsmouth | Cuesta A.,Yale University | Genova-Santos R.,Institute of Astrophysics of Canarias | And 17 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

In the context of the study of the integrated Sachs-Wolfe (ISW) effect, we construct a template of the projected density distribution up to redshift z ≃ 0.7 by using the luminous galaxies (LGs) from the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8).We use a photometric redshift catalogue trained with more than a hundred thousand galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) in the SDSS DR8 imaging area covering nearly one-quarter of the sky. We consider two different LG samples whose selection matches that of SDSS-III/BOSS: the low-redshift sample (LOWZ, z ε [0.15, 0.5]) and the constant mass sample (CMASS, z ε [0.4, 0.7]). When building the galaxy angular density templates we use the information from star density, survey footprint, seeing conditions, sky emission, dust extinction and airmass to explore the impact of these artefacts on each of the two LG samples. In agreement with previous studies, we find that the CMASS sample is particularly sensitive to Galactic stars, which dominate the contribution to the auto-angular power spectrum below l = 7. Other potential systematics affect mostly the very low multipole range (l ε [2, 7]), but leave fluctuations on smaller scales practically unchanged. The resulting angular power spectra in the multipole range l ε [2, 100] for the LOWZ, CMASS and LOWZ+CMASS samples are compatible with linear ∧ cold dark matter (∧CDM) expectations and constant bias values of b = 1.98 ± 0.11, 2.08 ± 0.14 and 1.88 ± 0.11, respectively, with no traces of non-Gaussianity signatures, i.e. flocal NL = 59 ± 75 at 95 per cent confidence level for the full LOWZ+CMASS sample in the multipole range l ε [4, 100]. After cross-correlatingWilkinson Microwave Anisotropy Probe 9-year datawith the LOWZ+CMASSLGprojected density field, the ISW signal is detected at the level of 1.62-1.69σ. While this result is in close agreement with theoretical expectations and predictions from realistic Monte Carlo simulations in the concordance ∧CDM model, it cannot rule out by itself an Einstein-de Sitter scenario, and has a moderately low signal compared to previous studies conducted on subsets of this LG sample. We discuss possible reasons for this apparent discrepancy, and point to uncertainties in the galaxy survey systematics as most likely sources of confusion. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Anderson L.,University of Washington | Aubourg E.,University Paris Diderot | Bailey S.,Lawrence Berkeley National Laboratory | Bizyaev D.,Apache Point Observatory | And 83 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present measurements of galaxy clustering from the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the Sloan Digital Sky Survey III (SDSS-III). These use the Data Release 9 (DR9) CMASS sample, which contains 264 283 massive galaxies covering 3275 square degrees with an effective redshift z = 0.57 and redshift range 0.43 < z < 0.7. Assuming a concordance λCDM cosmological model, this sample covers an effective volume of 2.2 Gpc3, and represents the largest sample of the Universe ever surveyed at this density, n̄ ~3 × 10-4 h-3 Mpc3. We measure the angle-averaged galaxy correlation function and power spectrum, including density-field reconstruction of the baryon acoustic oscillation (BAO) feature. The acoustic features are detected at a significance of 5σ in both the correlation function and power spectrum. Combining with the SDSS-II luminous red galaxy sample, the detection significance increases to 6.7σ. Fitting for the position of the acoustic features measures the distance to z = 0.57 relative to the sound horizon DV/rs = 13.67 ± 0.22 at z = 0.57. Assuming a fiducial sound horizon of 153.19 Mpc, which matches cosmic microwave background constraints, this corresponds to a distance DV (z = 0.57) = 2094 ± 34 Mpc. At 1.7 per cent, this is the most precise distance constraint ever obtained from a galaxy survey. We place this result alongside previous BAO measurements in a cosmological distance ladder and find excellent agreement with the current supernova measurements. We use these distance measurements to constrain various cosmological models, finding continuing support for a flat Universe with a cosmological constant. © 2012 The Authors. Source

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