Sabino Matarrese | Università degli Studi di Padova (original) (raw)

Papers by Sabino Matarrese

Mapping Measuring and Modelling the Universe, Jan 29, 1996

The non--linear dynamics of self--gravitating irrotational dust is analyzed in a general relativi... more The non--linear dynamics of self--gravitating irrotational dust is analyzed in a general relativistic framework, using synchronous and comoving coordinates. Writing the equations in terms of the metric tensor of the spatial sections orthogonal to the fluid flow allows an unambiguous expansion in inverse powers of the speed of light. The Newtonian and post--Newtonian approximations are derived in Lagrangian form. A general formula for the gravitational waves generated by the non--linear evolution of cosmological perturbations is given. It is argued that a stochastic gravitational--wave background is produced by non--linear cosmic structures, with present--day closure density Omegagwsim10−5\Omega_{gw} \sim 10^{-5}Omegagwsim10−5 -- 10−610^{-6}10−6 on Mpc scale.

Iau Joint Discussion, 2003

The Asiago-ESO/RASS QSO survey (AERQS) is a project aimed at the construction of an all-sky stati... more The Asiago-ESO/RASS QSO survey (AERQS) is a project aimed at the construction of an all-sky statistically well-defined sample of relatively bright QSOs (B<15) at z<0.3. We present the clustering analysis of the full spectroscopically identified database (392 AGN). The clustering signal at 0.02<z< 0.22 is detected at a 3-4s level and its amplitude is r0 = 8.6 +/- 2.0h-1 Mpc (in a LCDM model). The comparison with other classes of objects shows that low-redshift QSOs are clustered in a similar way to Radio Galaxies EROs and early-type galaxies although with a marginally smaller amplitude. The comparison with recent results from the 2QZ shows that the correlation function of QSOs is constant in redshift or marginally increasing toward low redshift. We discuss this behavior with physically motivated models deriving constraints on the typical mass of the dark matter halos hosting QSOs MDMH ~ 10 12.5 h-1 MQ . We use the clustering data to estimate the physical properties of local AGN obtaining MBH ~ 6.7 × 10-7 h-1 MQ for the mass of the active black holes tAGN ~ 4.4 × 106 yr for their life-time and e ~0.4 for their efficiency (always for a LCDM model).

Phys Rev D, 2005

The luminosity distance-redshift relation is one of the fundamental tools of modern cosmology. We... more The luminosity distance-redshift relation is one of the fundamental tools of modern cosmology. We compute the luminosity distance-redshift relation in a perturbed flat matter-dominated Universe, taking into account the presence of cosmological inhomogeneities up to second order in perturbation theory. Cosmological observations implementing the luminosity distance-redshift relation tell us that the Universe is presently undergoing a phase of accelerated expansion. This seems to call for a mysterious Dark Energy component with negative pressure. Our findings suggest that the need of a Dark Energy fluid may be challenged once a realistic inhomogeneous Universe is considered and that an accelerated expansion may be consistent with a matter-dominated Universe.

The general relativistic non--linear dynamics of a self--gravitating collisionless fluid with van... more The general relativistic non--linear dynamics of a self--gravitating collisionless fluid with vanishing vorticity is studied in synchronous and comoving -- i.e. {\em Lagrangian} -- coordinates. Writing the equations in terms of the metric tensor of the spatial sections orthogonal to the fluid flow allows an unambiguous expansion in inverse powers of the speed of light. The Newtonian and post--Newtonian approximations are derived in Lagrangian form; the non--linear evolution of the system on super--horizon scales, leading to the so--called ``silent universe", is also briefly discussed. A general formula for the gravitational waves generated by the non--linear evolution of cosmological perturbations is given: a stochastic gravitational--wave background is shown to be produced by non--linear cosmic structures, with present--day closure density Omegagwsim10−5\Omega_{gw} \sim 10^{-5}Omegagwsim10−5 -- 10−610^{-6}10−6 on the scale of 1 -- 10 Mpc.

Monthly Notices of the Royal Astronomical Society, Jul 6, 1997

Evidence that the Universe may be close to the critical density, required for its expansion event... more Evidence that the Universe may be close to the critical density, required for its expansion eventually to be halted, comes principally from dynamical studies of large-scale structure. These studies use the observed peculiar velocity field of galaxies either directly, or indirectly by quantifying its anisotropic effect on galaxy clustering in redshift surveys. A potential difficulty with both such approaches is that the density parameter Omega_0 is obtained only in the combination beta=Omega^0.6_0/b, if linear perturbation theory is used. The determination of the density parameter Omega_0 is therefore compromised by the lack of a good measurement of the bias parameter b, which relates the clustering of sample galaxies to the clustering of mass. In this paper, we develop an idea of Fry, using second-order perturbation theory to investigate how to measure the bias parameter on large scales. The use of higher order statistics allows the degeneracy between b and Omega_0 to be lifted, and an unambiguous determination of Omega_0 then becomes possible. We apply a likelihood approach to the bispectrum, the three-point function in Fourier space. This paper is the first step in turning the idea into a practical proposition for redshift surveys, and is principally concerned with noise properties of the bispectrum, which are non-trivial. The calculation of the required bispectrum covariances involves the six-point function, including many noise terms, for which we have developed a generating functional approach which will be of value in calculating high-order statistics in general.

We estimate analytically the second-order cosmic microwave background temperature anisotropies at... more We estimate analytically the second-order cosmic microwave background temperature anisotropies at the recombination epoch in the squeezed limit and we deduce the contamination of the primordial local non-Gaussianity. We find that the level of contamination corresponds to fNLcon = Script O(1) which is below the sensitivity of present experiments and smaller than the value Script O(5) recently claimed in the literature.

We study the power spectrum of galaxies in redshift space, with third order perturbation theory t... more We study the power spectrum of galaxies in redshift space, with third order perturbation theory to include corrections that are absent in linear theory. We assume a local bias for the galaxies: i.e. the galaxy density is sampled from some local function of the underlying mass distribution. We find that the effect of the nonlinear bias in real space is to introduce two new features: first, there is a contribution to the power which is constant with wavenumber, whose nature we reveal as essentially a shot-noise term. In principle this contribution can mask the primordial power spectrum, and could limit the accuracy with which the latter might be measured on very large scales. Secondly, the effect of second- and third-order bias is to modify the effective bias (defined as the square root of the ratio of galaxy power spectrum to matter power spectrum). The effective bias is almost scale-independent over a wide range of scales. These general conclusions also hold in redshift space. In addition, we have investigated the distortion of the power spectrum by peculiar velocities, which may be used to constrain the density of the Universe. We look at the quadrupole-to-monopole ratio, and find that higher-order terms can mimic linear theory bias, but the bias implied is neither the linear bias, nor the effective bias referred to above. We test the theory with biased N-body simulations, and find excellent agreement in both real and redshift space, providing the local biasing is applied on a scale whose fractional r.m.s. density fluctuations are <0.5< 0.5<0.5.

We discuss the question of gauge choice when analysing relativistic density perturbations at seco... more We discuss the question of gauge choice when analysing relativistic density perturbations at second order. We compare Newtonian and General Relativistic approaches. Some misconceptions in the recent literature are addressed. We show that the comoving-synchronous gauge is the unique gauge in General Relativity that corresponds to the Lagrangian frame and is entirely appropriate to describe the matter overdensity at second order. The comoving-synchronous gauge is the simplest gauge in which to describe Lagrangian bias at second order.

This is the third paper of a series describing the Asiago-ESO/RASS QSO survey (AERQS), a project ... more This is the third paper of a series describing the Asiago-ESO/RASS QSO survey (AERQS), a project aimed at the construction of an all-sky statistically well-defined sample of relatively bright QSOs (B<15) at z<0.3. We present here the clustering analysis of the full spectroscopically identified database (392 AGN). The clustering signal at 0.02<z<0.22 is detected at a 3-4 sigma level and its amplitude is measured to be r_0=8.6\pm 2.0 h^{-1} Mpc (in a LambdaCDM model). The comparison with other classes of objects shows that low-redshift QSOs are clustered in a similar way to Radio Galaxies, EROs and early-type galaxies in general, although with a marginally smaller amplitude. The comparison with recent results from the 2QZ shows that the correlation function of QSOs is constant in redshift or marginally increasing toward low redshift. We discuss this behavior with physically motivated models, deriving interesting constraints on the typical mass of the dark matter halos hosting QSOs, M_DMH= 10^{12.7} h^{-1} M_sun (10^{12.0}-10^{13.5}h^{-1} M_sun at 1 sigma confidence level). Finally, we use the clustering data to infer the physical properties of local AGN, obtaining M_BH=2 10^8 h^{-1} M_sun (10^7-3 10^9 h^{-1} M_sun) for the mass of the active black holes, tau_{AGN}= 8 10^6 yr (2 10^{6}-5 10^{7} yr) for their life-time and eta = 0.14 for their efficiency (always for a LambdaCDM model).

The Astrophysical Journal Letters, Jan 31, 2008

It has long been known how to analytically relate the clustering properties of the collapsed stru... more It has long been known how to analytically relate the clustering properties of the collapsed structures (halos) to those of the underlying dark matter distribution for Gaussian initial conditions. Here we apply the same approach to physically motivated non-Gaussian models. The techniques we use were developed in the 1980s to deal with the clustering of peaks of non-Gaussian density fields. The description of the clustering of halos for non-Gaussian initial conditions has recently received renewed interest, motivated by the forthcoming large galaxy and cluster surveys. For inflationary-motivated non-Gaussianities, we find an analytic expression for the halo bias as a function of scale, mass, and redshift, employing only the approximations of high peaks and large separations.

Physical Review Letters, 1994

The nonlinear dynamics of cosmological perturbations of an irrotational collisionless fluid is an... more The nonlinear dynamics of cosmological perturbations of an irrotational collisionless fluid is analyzed within general relativity. Relativistic and Newtonian solutions are compared, stressing the different role of boundary conditions in the two theories. Cosmological implications of relativistic effects, already present at second order in perturbation theory, are studied and the dynamical role of the magnetic part of the Weyl tensor is elucidated.

Astron Astrophys, 2003

A new method for reconstruction of the primordial density fluctuation field is presented. Various... more A new method for reconstruction of the primordial density fluctuation field is presented. Various previous approaches to this problem rendered non-unique solutions. Here, it is demonstrated that the initial positions of dark matter fluid elements, under the hypothesis that their displacement is the gradient of a convex potential, can be reconstructed uniquely. In our approach, the cosmological reconstruction problem is reformulated as an assignment problem in optimization theory. When tested against numerical simulations, our scheme yields excellent reconstruction on scales larger than a few megaparsecs.

The Astrophysical Journal, Apr 10, 1995

Phys Rev D, 2002

Correlated adiabatic and isocurvature perturbation modes are produced during inflation through an... more Correlated adiabatic and isocurvature perturbation modes are produced during inflation through an oscillation mechanism when extra scalar degrees of freedom, other than the inflaton field, are present. We show that this correlation generically leads to sizable non-Gaussian features both in the adiabatic and isocurvature perturbations. The non-Gaussianity is first generated by large nonlinearities in some scalar sector and then efficiently transferred to the inflaton sector by the oscillation process. We compute the cosmic microwave background angular bispectrum, providing a characteristic feature of such inflationary non-Gaussianity, which might be detected by upcoming satellite experiments.

Journal of Cosmology and Astroparticle Physics, 2008

Inflationary observables, like the power spectrum, computed at one-order and higher-order loop le... more Inflationary observables, like the power spectrum, computed at one-order and higher-order loop level seem to be plagued by large infra-red corrections. In this short note, we point out that these large infra-red corrections appear only in quantities which are not directly observable. This is in agreement with general expectations concerning infra-red effects.

Phys Rev D, 2004

Since a positive future detection of nonlinearity in the cosmic microwave background anisotropy p... more Since a positive future detection of nonlinearity in the cosmic microwave background anisotropy pattern might allow us to descriminate among different mechanisms giving rise to cosmological adiabatic perturbations, we study the evolution of the second-order cosmological curvature perturbation on superhorizon scales in the curvaton scenario. We provide the exact expression for the non-Gaussianity in the primordial perturbations including gravitational second-order corrections which are particularly relevant in the case in which the curvaton dominates the energy density before it decays. As a by-product, we show that in the standard scenario where cosmological curvature perturbations are induced by the inflaton field, the second-order curvature perturbation is conserved even during the reheating stage after inflation.

We study the clustering properties of the galaxy clusters detectable for the Planck satellite due... more We study the clustering properties of the galaxy clusters detectable for the Planck satellite due to their thermal Sunyaev-Zel'dovich effect. We take the past light-cone effect and the redshift evolution of both the underlying dark matter correlation function and the cluster bias factor into account. A theoretical mass-temperature relation allows us to convert the sensitivity limit of a catalogue into a minimum mass for the dark matter haloes hosting the clusters. We confirm that the correlation length is an increasing function of the sensitivity limits defining the survey. Using the expected characteristics of the Planck cluster catalogue, which will be a quite large and unbiased sample, we predict the two-point correlation function and power spectrum for different cosmological models. We show that the wide redshift distribution of the Planck survey, will allow to constrain the cluster clustering properties up to z=1. The dependence of our results on the main cosmological parameters (the matter density parameter, the cosmological constant and the normalisation of the density power-spectrum) is extensively discussed. We find that the future Planck clustering data place only mild constraints on the cosmological parameters, because the results depend on the physical characteristics of the intracluster medium, like the baryon fraction and the mass-temperature relation. Once the cosmological model and the Hubble constant are determined, the clustering data will allow a determination of the baryon fraction with an accuracy of few per cent.