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Matter Power Spectrum (matter + power_spectrum)
Selected AbstractsHalo stochasticity in global clustering analysisMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009S. Bonoli ABSTRACT Galaxy clustering and cosmic magnification can be used to estimate the dark matter power spectrum if the theoretical relation between the distribution of galaxies and the distribution of dark matter is precisely known. In the present work, we study the statistics of haloes, which in the halo model determines the distribution of galaxies. Haloes are known to be biased tracer of dark matter, and at large scales it is usually assumed there is no intrinsic stochasticity between the two field (i.e. r= 1). Following the work of Seljak & Warren, we explore how correct this assumption is and, moving a step further, we try to qualify the nature of stochasticity. We use principal component analysis applied to the outputs of a cosmological N -body simulation as a function of mass to: (i) explore the behaviour of stochasticity in the correlation between haloes of different masses; and (ii) explore the behaviour of stochasticity in the correlation between haloes and dark matter. We show results obtained using a catalogue with 2.1 million haloes, from a pmfast simulation with box size of 1000 h,1 Mpc and with about four billion particles. In the relation between different populations of haloes, we find that stochasticity is not negligible even at large scales. In agreement with the conclusions of Tegmark & Bromley, who studied the correlations of different galaxy populations, we found that the shot noise subtracted stochasticity is qualitatively different from ,enhanced' shot noise and, specifically, it is dominated by a single stochastic eigenvalue. We call this the ,minimally stochastic' scenario, as opposed to shot noise-like stochasticity which is ,maximally stochastic'. In the correlation between haloes and dark matter, we find that the stochasticity is minimized, as expected, near the dark matter peak (k, 0.02 h Mpc,1 for a , cold dark matter cosmology), and, even at large scales, it is of the order of 15 per cent above the shot noise. Moreover, we find that the reconstruction of the dark matter distribution is improved when we use the principal component eigenvectors as tracers of the bias, but still the reconstruction is not perfect, due to stochasticity. [source] Beating lensing cosmic variance with galaxy tomographyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2004Ue-Li Pen ABSTRACT We discuss the use of cross-correlations between galaxies with distance information and projected weak lensing dark matter maps to obtain a fully three-dimensional dark matter map and power spectrum. On large scales (l, 100) one expects the galaxies to be biased, but not stochastic. I show that this allows a simultaneous solution of the full three-dimensional evolving galaxy bias and the dark matter power spectrum simultaneously. Within the photometric redshift information of the Canada,France,Hawaii (CFH) lensing legacy survey, this allows a threefold reduction of statistical error, while a cross-correlation with the Canadian Large Adaptive Reflector (CLAR) or other deep spectroscopic surveys allows a tenfold improvement in dark matter power accuracy on linear scales. This makes lensing surveys more sensitive to the cosmic equation of state and the neutrino masses. [source] Constraints on the cosmic neutrino backgroundMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2003Elena Pierpaoli ABSTRACT The radiative component of the Universe has a characteristic impact on both large-scale structure (LSS) and the cosmic microwave background radiation (CMB). We use the recent WMAP data, together with previous Cosmic Background Imager (CBI) data and 2dF matter power spectrum, to constrain the effective number of neutrino species Neff in a general cosmology. We find that Neff= 4.31 with a 95 per cent confidence limit 1.6 ,Neff, 7.1. If we include the H0 prior from the HST project we find the best fit Neff= 4.08 and 1.90 ,Neff, 6.62 for a 95 per cent confidence limit. The curvature we derive is still consistent with flat, but assuming a flat Universe from the beginning implies a bias toward lower Neff, as well as artificially smaller error bars. Adding the supernova constraint does not improve the result. We analyse and discuss the degeneracies with other parameters, and point out that probes of the matter power spectrum on smaller scales and accurate independent ,8 measurements, together with better independent measurement of H0, would help in breaking the degeneracies. [source] Merger histories in warm dark matter structure formation scenariosMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2002Alexander Knebe Observations on galactic scales seem to be in contradiction with recent high-resolution N -body simulations. This so-called cold dark matter (CDM) crisis has been addressed in several ways, ranging from a change in fundamental physics by introducing self-interacting cold dark matter particles to a tuning of complex astrophysical processes such as global and/or local feedback. All these efforts attempt to soften density profiles and reduce the abundance of satellites in simulated galaxy haloes. In this paper, we explore a different approach that consists of filtering the dark matter power spectrum on small scales, thereby altering the formation history of low-mass objects. The physical motivation for damping these fluctuations lies in the possibility that the dark matter particles have a different nature, i.e. are warm (WDM) rather than cold. We show that this leads to some interesting new results in terms of the merger history and large-scale distribution of low-mass haloes, compared with the standard CDM scenario. However, WDM does not appear to be the ultimate solution, in the sense that it is not able to fully solve the CDM crisis, even though one of the main drawbacks, namely the abundance of satellites, can be remedied. Indeed, the cuspiness of the halo profiles still persists, at all redshifts, and for all haloes and sub-haloes that we investigated. Despite the persistence of the cuspiness problem of DM haloes, WDM seems to be still worth taking seriously, as it alleviates the problems of over-abundant sub-structures in galactic haloes and possibly the lack of angular momentum of simulated disc galaxies. WDM also lessens the need to invoke strong feedback to solve these problems, and may provide a natural explanation of the clustering properties and ages of dwarfs. [source] Cosmic momentum field and mass fluctuation power spectrumMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000Changbom Park We introduce the cosmic momentum field as a new measure of the large-scale peculiar velocity and matter fluctuation fields. The momentum field is defined as the peculiar velocity field traced and weighted by galaxies, and is equal to the velocity field in the linear regime. We show that the radial component of the momentum field can be considered as a scalar field with the power spectrum which is practically one-third of that of the total momentum field. We present a formula for the power spectrum directly calculable from the observed radial peculiar velocity data. The momentum power spectrum is measured for the MAT sample in the Mark III catalogue of peculiar velocities of galaxies. Using the momentum power spectrum we find the amplitude of the matter power spectrum is and at the wavenumbers 0.049 and 0.074 h Mpc,1, respectively, where , is the density parameter. The 68 per cent confidence limits include the cosmic variance. The measured momentum and density power spectra together indicate that the parameter or where bO is the bias factor for optical galaxies. [source] Probing dark matter, galaxies and the expansion history of the Universe with Ly, in absorption and emissionASTRONOMISCHE NACHRICHTEN, Issue 5 2010M.G. Haehnelt Abstract Ly, radiation is an important diagnostic tool in a wide range of astrophysical environments. I will first describe here how measurements of the matter power spectrum on small scales from Ly, forest data constrain the mass of dark matter particles. I then will report on an ambitious program of searching for very faint spatially extended Ly, emission at z , 3 which has led to the discovery of a new population of faint Ly, emitters which I will argue should be identified with the long searched for host galaxies of damped Ly, absorbers. Finally, I will discuss the possibility of measuring the redshift drift of Ly, absorption features and therefore the change of the expansion rate of the Universe in real time with the ultra-stable high-resolution spectrograph CODEX proposed for the E-ELT (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||