Institute Of Ciencies Of Lespai

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Institute Of Ciencies Of Lespai

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Crocce M.,Institute Of Ciencies Of Lespai | Cabre A.,University of Pennsylvania | Gaztanaga E.,Institute Of Ciencies Of Lespai
Monthly Notices of the Royal Astronomical Society | Year: 2011

Near-future cosmology will see the advent of wide-area photometric galaxy surveys, such as the Dark Energy Survey (DES), that extend to high redshifts (z~ 1-2) but give poor radial distance resolution. In such cases splitting the data into redshift bins and using the angular correlation function w(θ), or the Cℓ power spectrum, will become the standard approach to extracting cosmological information or to studying the nature of dark energy through the baryon acoustic oscillations (BAO) probe. In this work we present a detailed model for w(θ) at large scales as a function of redshift and binwidth, including all relevant effects, namely non-linear gravitational clustering, bias, redshift space distortions and photo-z uncertainties. We also present a model for the full covariance matrix, characterizing the angular correlation measurements, that takes into account the same effects as for w(θ) and also the possibility of a shot-noise component and partial sky coverage. Provided with a large-volume N-body simulation from the MICE collaboration, we built several ensembles of mock redshift bins with a sky coverage and depth typical of forthcoming photometric surveys. The model for the angular correlation and the one for the covariance matrix agree remarkably well with the mock measurements in all configurations. The prospects for a full shape analysis of w(θ) at BAO scales in forthcoming photometric surveys such as DES are thus very encouraging. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Anselmi S.,Institute Of Ciencies Of Lespai | Pietroni M.,National Institute of Nuclear Physics, Italy
Journal of Cosmology and Astroparticle Physics | Year: 2012

A new computational scheme for the nonlinear cosmological matter power spectrum (PS) is presented. Our method is based on evolution equations in time, which can be cast in a form extremely convenient for fast numerical evaluations. A nonlinear PS is obtained in a time comparable to that needed for a simple 1-loop computation, and the numerical implementation is very simple. Our results agree with N-body simulations at the percent level in the BAO range of scales, and at the few-percent level up to k ≃ 1 h/Mpc at z≳0.5, thereby opening the possibility of applying this tool to scales interesting for weak lensing. We clarify the approximations inherent to this approach as well as its relations to previous ones, such as the Time Renormalization Group, and the multi-point propagator expansion. We discuss possible lines of improvements of the method and its intrinsic limitations by multi streaming at small scales and low redshifts. © 2012 IOP Publishing Ltd and Sissa Medialab srl.

Bernardeau F.,CEA Saclay Nuclear Research Center | Bernardeau F.,French National Center for Scientific Research | Crocce M.,Institute Of Ciencies Of Lespai | Scoccimarro R.,New York University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We present a new scheme for the general computation of cosmic propagators that allow to interpolate between standard perturbative results at low k and their expected large-k resummed behavior. This scheme is applicable to any multipoint propagator and allows the matching of perturbative low-k calculations to any number of loops to their large-k behavior, and can potentially be applied in case of nonstandard cosmological scenarios such as those with non-Gaussian initial conditions. The validity of our proposal is checked against previous prescriptions and measurements in numerical simulations showing a remarkably good agreement. Such a generic prescription for multipoint propagators provides the necessary building blocks for the computation of polyspectra in the context of the so-called Γ expansion introduced by F. Bernardeau, M. Crocce, and R. ScoccimarroPhys. Rev. DPRVDAQ1550-7998 78, 103521 (2008).10.1103/PhysRevD.78.103521. As a concrete application we present a consistent calculation of the matter bispectrum at one-loop order. © 2012 American Physical Society.

Amaro-Seoane P.,Max Planck Institute For Gravitationsphysik Albert Einstein Institute | Amaro-Seoane P.,Institute Of Ciencies Of Lespai | Santamaria L.,Max Planck Institute For Gravitationsphysik Albert Einstein Institute
Astrophysical Journal | Year: 2010

Even though the existence of intermediate-mass black holes (IMBHs; black holes with masses ranging between 102 M⊙ and 104 M⊙) has not yet been corroborated observationally, these objects are of high interest for astrophysics. Our understanding of the formation and evolution of supermassive black holes, as well as galaxy evolution modeling and cosmography would dramatically change if an IMBH were to be observed. From the point of view of traditional photon-based astronomy, which relies on the monitoring of innermost stellar kinematics, the direct detection of an IMBH seems to be rather far in the future. However, the prospect of the detection and characterization of an IMBH has good chances in lower frequency gravitational-wave (GW) astrophysics using ground-based detectors such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), Virgo, and the future Einstein Telescope (ET). We present an analysis of the signal of a system of a binary of IMBHs based on a waveform model obtained with numerical relativity simulations coupled with post-Newtonian calculations at the highest available order. IMBH binaries with total masses between 200 and 20,000 M⊙ would produce significant signal-to-noise ratios in Advanced LIGO and Virgo and the ET. We have computed the expected event rate of IMBH binary coalescences for different configurations of the binary, finding interesting values that depend on the spin of the IMBHs. The prospects for IMBH detection and characterization with ground-based GW observatories would not only provide us with a robust test of general relativity, but would also corroborate the existence of these systems. Such detections should allow astrophysicists to probe the stellar environments of IMBHs and their formation processes. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Manera M.,University of Portsmouth | Manera M.,New York University | Gaztanaga E.,Institute Of Ciencies Of Lespai
Monthly Notices of the Royal Astronomical Society | Year: 2011

We explore the biasing in the clustering statistics of haloes as compared to dark matter (DM) in simulations. We look at the second- and third-order statistics at large scales of the (intermediate) MICEL1536 simulation and also measure directly the local bias relation h=f(δ) between DM fluctuations, δ, smoothed over a top-hat radius Rs at a point in the simulation and its corresponding tracer h (i.e. haloes) at the same point. This local relation can be Taylor expanded to define a linear (b1) and non-linear (b2) bias parameter. The values of b1 and b2 in the simulation vary with Rs approaching a constant value around Rs > 30-60Mpch-1. We use the local relation to predict the clustering of the tracer in terms of the one of DM. This prediction works very well (about per cent level) for the halo 2-point correlation ξ(r12) for r12 > 15 Mpch-1, but only when we use the biasing values that we found at very large smoothing radii Rs > 30-60Mpch-1. We find no effect from stochastic or next-to-leading-order terms in the f(δ) expansion. However, we do find some discrepancies in the 3-point function that needs further understanding. We also look at the clustering of the smoothed moments, the variance and skewness which are volume-average correlations and therefore include clustering from smaller scales. In this case, we find that both next-to-leading-order and discreteness corrections (to the local model) are needed at the 10-20 per cent level. Shot-noise can be corrected with a term, where σ2e < 1, that is, always smaller than the Poisson correction. We also compare these results with the peak-background split predictions from the measured halo mass function. We find 5-10 per cent systematic (and similar statistical) errors in the mass estimation when we use the halo model biasing predictions to calibrate the mass. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Pujol A.,Institute Of Ciencies Of Lespai | Gaztanaga E.,Institute Of Ciencies Of Lespai
Monthly Notices of the Royal Astronomical Society | Year: 2014

We study how well we can reconstruct the two-point clustering of galaxies on linear scales, as a function of mass and luminosity, using the halo occupation distribution (HOD) in several semi-analytical models (SAMs) of galaxy formation from the Millennium Simulation. We find that the HOD with Friends-of-Friends groups can reproduce galaxy clustering better than gravitationally bound haloes. This indicates that Friends-of-Friends groups are more directly related to the clustering of these regions than the bound particles of the overdensities. In general, we find that the reconstruction works at best to ≃5 per cent accuracy: it underestimates the bias for bright galaxies. This translates to an overestimation of 50 per cent in the halo mass when we use clustering to calibrate mass. We also found a degeneracy on the mass prediction from the clustering amplitude that affects all the masses. This effect is due to the clustering dependence on the host halo substructure, an indication of assembly bias. We show that the clustering of haloes of a given mass increases with the number of subhaloes, a result that only depends on the underlying matter distribution. As the number of galaxies increases with the number of subhaloes in SAMs, this results in a low bias for the HOD reconstruction. We expect this effect to apply to other models of galaxy formation, including the real Universe, as long as the number of galaxies increases with the number of subhaloes. We have also found that the reconstructions of galaxy bias from the HOD model fail for low-mass haloes with M ≲ 3-5 × 1011 h-1M⊙. We find that this is because galaxy clustering is more strongly affected by assembly bias for these low masses. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Rius A.,Institute Of Ciencies Of Lespai | Cardellach E.,Institute Of Ciencies Of Lespai | Martin-Neira M.,European Space Agency
IEEE Transactions on Geoscience and Remote Sensing | Year: 2010

We describe the development and implementation of a method for extracting altimetric information using the Passive Reflectometry and Interferometry System (PARIS), i.e., from GPS signals after their reflection off the sea surface. We have formalized one idea laid out in the description of a bistatic system for ocean altimetry using the GPS signal, by Hajj and Zuffada (Jet Propulsion Laboratory), and have extended it to real situations encountered in PARIS aircraft experiments. Second, we have developed the corresponding algorithms to produce real-time altimetric observables to be used in dedicated digital signal processors. Finally, we have applied this method to estimate sea-surface height from one flight experiment in the North Sea off the coast of Norway. © 2010 IEEE.

Bonnett C.,Institute Of Ciencies Of Lespai | Bonnett C.,Autonomous University of Barcelona
Monthly Notices of the Royal Astronomical Society | Year: 2015

We present a novel way of using neural networks (NN) to estimate the redshift distribution of a galaxy sample. We are able to obtain a probability density function (PDF) for each galaxy using a classification NN. The method is applied to 58 714 galaxies in CFHTLenS that have spectroscopic redshifts from DEEP2, VVDS and VIPERS. Using this data, we show that the stacked PDFs give an excellent representation of the true N(z) using information from 5, 4 or 3 photometric bands. We show that the fractional error due to using N(zphot) instead of N(ztruth) is ≤1 per cent on the lensing power spectrum (Pκ ) in several tomographic bins. Further, we investigate how well this method performs when few training samples are available and show that in this regime the NN slightly overestimates the N(z) at high z. Finally, the case where the training sample is not representative of the full data set is investigated. © 2015 The Authors.

Bernardeau F.,CEA Saclay Nuclear Research Center | Crocce M.,Institute Of Ciencies Of Lespai | Sefusatti E.,CEA Saclay Nuclear Research Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

We show here how renormalized perturbation theory calculations applied to the quasilinear growth of the large-scale structure can be carried on in presence of primordial non-Gaussian (PNG) initial conditions. It is explicitly demonstrated that the series reordering scheme proposed in Bernardeau, Crocce, and Scoccimarro [Phys. Rev. D 78, 103521 (2008)] is preserved for non-Gaussian initial conditions. This scheme applies to the power spectrum and higher-order spectra and is based on a reorganization of the contributing terms into the sum of products of multipoint propagators. In case of PNG, new contributing terms appear, the importance of which is discussed in the context of current PNG models. The properties of the building blocks of such resummation schemes, the multipoint propagators, are then investigated. It is first remarked that their expressions are left unchanged at one-loop order irrespective of statistical properties of the initial field. We furthermore show that the high-momentum limit of each of these propagators can be explicitly computed even for arbitrary initial conditions. They are found to be damped by an exponential cutoff whose expression is directly related to the moment generating function of the one-dimensional displacement field. This extends what had been established for multipoint propagators for Gaussian initial conditions. Numerical forms of the cutoff are shown for the so-called local model of PNG. © 2010 The American Physical Society.

Hernanz M.,Institute Of Ciencies Of Lespai
Bulletin of the Astronomical Society of India | Year: 2012

Classical novae produce radioactive nuclei which are emitters of γ-rays in the MeV range. Some examples are the lines at 478 and 1275 keV (from 7Be and 22Na) and the positron-electron annihilation emission (511 keV line and a continuum below this energy, with a cut-off at 20-30 keV). The analysis of γ-ray spectra and light curves is potentially a unique and powerful tool both to trace the corresponding isotopes and to give insights on the properties of the expanding envelope determining its transparency. Another possible origin of γ-rays is the acceleration of particles up to very high energies, so that either neutral pions or inverse Compton processes produce γ-rays of energies larger than 100 MeV. MeV photons during nova explosions have not been detected yet, although several attempts have been made in the last decades; on the other hand, GeV photons from novae have been detected in some particular novae, in symbiotic binaries, where the companion is a red giant with a wind, instead of a main sequence star as in the cataclysmic variables hosting classical novae. Both mechanisms of γ-ray production in novae are reviewed, with more emphasis on the one related to radioactivities.

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