Power Spectrum Of Mass Fluctuations Research Articles

Peaks in the cosmological density field: parameter constraints from 2dF Galaxy Redshift Survey data

We use the number density of peaks in the smoothed cosmological density field taken from the 2dF Galaxy Redshift Survey to constrain parameters related to the power spectrum of mass fluctuations, n (the spectral index), dn/d(lnk) (rolling in the spectral index), and the neutrino mass, m_nu. In a companion paper we use N-body simulations to study how the peak density responds to changes in the power spectrum, the presence of redshift distortions and the relationship between galaxies and dark matter halos. In the present paper we make measurements of the peak density from 2dF Galaxy Redshift Survey data, for a range of smoothing filter scales from 4-33 h^-1 Mpc. We use these measurements to constrain the cosmological parameters, finding n=1.36 (+0.75)(-0.64), m_nu < 1.76 eV, dn/d(lnk)=-0.012 (+0.192)(-0.208), at the 68 % confidence level, where m_nu is the total mass of three massive neutrinos. At 95% confidence we find m_nu< 2.48 eV. These measurements represent an alternative way to constrain cosmological parameters to the usual direct fits to the galaxy power spectrum, and are expected to be relatively insensitive to non-linear clustering evolution and galaxy biasing.

Imprints of deviations from the gravitational inverse-square law on the power spectrum of mass fluctuations

Deviations from the gravitational inverse-square law would imprint scale-dependent features on the power spectrum of mass density fluctuations. We model such deviations as a Yukawa-like contribution to the gravitational potential and discuss the growth function in a mixed dark matter model with adiabatic initial conditions. Evolution of perturbations is considered in general non-flat cosmological models with a cosmological constant, and an analytical approximation for the growth function is provided. The coupling between baryons and cold dark matter across recombination is negligibly affected by modified gravity physics if the proper cut-off length of the long-range Yukawa-like force is ≳10 h−1 Mpc. Enhancement of gravity affects the subsequent evolution, boosting large-scale power in a way that resembles the effect of a lower matter density. This phenomenon is almost perfectly degenerate in power-spectrum shape with the effect of a background of massive neutrinos. Back-reaction on density growth from a modified cosmic expansion rate should, however, also affect the normalization of the power spectrum, with a shape distortion similar to the case of a non-modified background.

A Cosmological Kinetic Theory for the Evolution of Cold Dark Matter Halos with Substructure: Quasi‐Linear Theory

We present a kinetic theory for the evolution of the phase-space distribution of dark matter particles in galaxy halos in the presence of a cosmological spectrum of fluctuations. This theory introduces a new way to model the formation and evolution of halos, which traditionally have been investigated by analytic gravitational infall models or numerical N-body methods. Unlike the collisionless Boltzmann equation, our kinetic equation contains nonzero terms on the right-hand side arising from stochastic fluctuations in the gravitational potential due to substructures in the dark matter mass distribution. Using statistics for constrained Gaussian random fields in standard cosmological models, we show that our kinetic equation to second order in perturbation theory is of the Fokker-Planck form, with one scattering term representing drift and the other representing diffusion in velocity space. The drift is radial, and the drift and diffusion coefficients depend only on positions and not velocities; our relaxation process in the quasi-linear regime is therefore different from the standard two-body relaxation. We provide explicit expressions relating these coefficients to the linear power spectrum of mass fluctuations and present results for the currently favored cold dark matter model with a nonzero cosmological constant. Solutions to this kinetic equation will provide a complete description of the cold dark matter spatial and velocity distributions for the average halo during the early phases of galaxy halo formation.

X‐Ray Temperatures for the Extended Medium‐Sensitivity Survey High‐Redshift Cluster Sample: Constraints on Cosmology and the Dark Energy Equation of State

We measure the X-ray temperature (and luminosity) with ASCA of all but one cluster in the Einstein Extended Medium-Sensitivity Survey (EMSS) high-redshift (z ≥ 0.3) sample. We compare these data to a complete sample of low-redshift clusters that also has temperature measurements, thereby providing cosmological constraints. Improvements over our previous work include (1) an enlarged high-redshift sample; (2) temperatures for the low-redshift comparison sample that come from the same instrument as the high-redshift sample; (3) the elimination of three EMSS clusters with the same redshift as the target (i.e., not truly serendipitous) and a fourth with an ASCA flux well below the completeness limit; (4) using a theoretical cluster mass function that more closely matches N-body simulations (the Sheth-Torman function); (5) using a cold dark matter power spectrum instead of a power law; (6) using a general cosmology with arbitrary matter density and cosmological constant; (7) using a cosmology that generalizes the cosmological constant to quintessence; (8) including the effects of temperature measurement errors and scatter in the cluster luminosity-temperature relation; and (9) marginalizing over the poorly known normalization of the mass-temperature relation. We find an allowed band in the Ωm0-ΩΛ0 plane of different orientation to the band of constraints provided by the supernovae Ia Hubble diagram and the cosmic microwave background fluctuations. All three bands intersect at the same place: Ωm0 ≈ 0.3, ΩΛ0 ≈ 0.7. We measure the quintessence equation-of-state parameter to be w = -(0.42 ± 0.21) (68% confidence for one interesting parameter), consistent with previously determined upper limits. We measure the normalization of the mass fluctuation power spectrum to be σ8 = 0.66 ± 0.16 (68% confidence for three interesting parameters). Systematic errors are larger than the statistical errors only for σ8 with our sample; thus the errors for it depend on the details of the marginalization over the temperature-mass normalization.

Early Quintessence in Light of the Wilkinson Microwave Anisotropy Probe

We examine the cosmic microwave background (CMB) anisotropy for signatures of early quintessence dark energy—a nonnegligible quintessence energy density during the recombination and structure formation eras. Only very recently does the quintessence overtake the dark matter and push the expansion into overdrive. Because the presence of early quintessence exerts an influence on the clustering of dark matter and the baryon-photon fluid, we may expect to find trace signals in the CMB and the mass fluctuation power spectrum. In detail, we demonstrate that suppressed clustering power on small length scales, as suggested by the combined Wilkinson Microwave Anisotropy Probe/CMB/large-scale structure data set, is characteristic of early quintessence. We identify a set of concordant models and map out directions for further investigation of early quintessence.

Cosmological constraints from the local X-ray luminosity function of the most X-ray-luminous galaxy clusters

We present precise constraints on the normalization of the power spectrum of mass fluctuations in the nearby universe, sigma_8, as a function of the mean local matter density, Omega_m. Using the observed local X-ray luminosity function of galaxy clusters from the extended BCS and REFLEX studies, a mass-luminosity relation determined from Chandra and ROSAT X-ray data and weak gravitational lensing observations, and the mass function predicted by the Hubble Volume simulations of Evrard et al., we obtain sigma_8 = (0.508\pm0.019) Omega_m^-(0.253\pm0.024), with Omega_m < 0.34 at 68 per cent confidence. The degeneracy between sigma_8 and Omega_m can be broken using Chandra measurements of the X-ray gas mass fractions in dynamically relaxed clusters. Using this information and including Gaussian priors on the mean baryon density of the universe and the Hubble constant, we obtain sigma_8=0.695\pm0.042 and Omega_m=0.287\pm0.036, for an assumed flat LambdaCDM cosmology (marginalized 68 per cent confidence limits). Our results are in good agreement with some recent studies based on the local X-ray temperature function of clusters, the redshift evolution of the X-ray luminosity and temperature functions of clusters, early results from the Sloan Digitized Sky Survey, the most recent results from studies of cosmic shear, and combined analyses of the 2dF galaxy redshift survey and cosmic microwave background anisotropies.

Cosmic momentum field and mass fluctuation power spectrum

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 Ω 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.

Cosmic momentum field and mass fluctuation power spectrum

Cosmic momentum field and mass fluctuation power spectrum

Fluid Dark Matter.

Dark matter modeled as a classical scalar field that interacts only with gravity and with itself by a potential that is close to quartic at large field values and approaches a quadratic form when the field is small would be gravitationally produced by inflation and, at the present epoch, could act like an ideal fluid with pressure that is a function only of the mass density. This could have observationally interesting effects on the core radii and solid-body rotation of dark matter halos and on the low-mass end of the primeval mass fluctuation power spectrum.

The Power Spectrum of Mass Fluctuations Measured from the Lyα Forest at Redshiftz = 2.5

We measure the linear power spectrum of mass-density fluctuations at redshift z = 2.5 from the Lyα forest absorption in a sample of 19 QSO spectra, using the method introduced by Croft et al. The P(k) measurement covers the range 2π/k ~ 450-2350 km s-1 (2-12 comoving h-1 Mpc for Ω = 1), limited on the upper end by uncertainty in fitting the unabsorbed QSO continuum and on the lower end by finite spectral resolution (0.8-2.3 A FWHM) and by nonlinear dynamical effects. We examine a number of possible sources of systematic error and find none that are significant on these scales. In particular, we show that spatial variations in the UV background caused by the discreteness of the source population should have negligible effect on our P(k) measurement. We estimate statistical errors by dividing the data set into ten subsamples. The statistical uncertainty in the rms mass-fluctuation amplitude, σ [P(k)]1/2, is ~20%, and is dominated by the finite number of spectra in the sample. We obtain consistent P(k) measurements (with larger statistical uncertainties) from the high- and low-redshift halves of the data set, and from an entirely independent sample of nine QSO spectra with mean redshift z = 2.1. A power-law fit to our results yields a logarithmic slope n = -2.25 ± 0.18 and an amplitude Δ2ρ(kp) = 0.57+0.26-0.18, where Δ2ρ is the contribution to the density variance from a unit interval of ln k and kp = 0.008(km s-1)-1. Direct comparison of our mass P(k) to the measured clustering of Lyman break galaxies shows that they are a highly biased population, with a bias factor b ~ 2-5. The slope of the linear P(k), never previously measured on these scales, is close to that predicted by models based on inflation and cold dark matter (CDM). The P(k) amplitude is consistent with some scale-invariant, COBE-normalized CDM models (e.g., an open model with Ω0 = 0.4) and inconsistent with others (e.g., Ω = 1). Even with limited dynamic range and substantial statistical uncertainty, a measurement of P(k) that has no unknown bias factors offers many opportunities for testing theories of structure formation and constraining cosmological parameters.

Recovery of the Power Spectrum of Mass Fluctuations from Observations of the Lyα Forest

We present a method to recover the shape and amplitude of the power spectrum of mass fluctuations, P(k), from observations of the high-redshift Lyα forest. The method is motivated by the physical picture that has emerged from hydrodynamic cosmological simulations and related semianalytic models, in which typical Lyα forest lines arise in a diffuse, continuous, fluctuating intergalactic medium. The thermal state of this low-density gas (δρ/ρ 10) is governed by simple physical processes, which lead to a tight correlation between the Lyα optical depth and the underlying matter density. To recover the mass power spectrum, we (1) apply a monotonic Gaussian mapping to convert the QSO spectrum to an approximate line-of-sight density field with arbitrary normalization, (2) measure the power spectrum of this continuous density field and convert it to the equivalent three-dimensional P(k), and (3) evolve cosmological simulations with this P(k) shape and a range of normalizations and choose the normalization for which the simulations reproduce the observed power spectrum of the transmitted QSO flux. Imposing the observed mean Lyα opacity as a constraint in step (3) makes the derived P(k) normalization insensitive to the choice of cosmological parameters, ionizing background spectrum, or reionization history. Thus, in contrast to estimates of P(k) from galaxy clustering, there are no uncertain bias parameters in the recovery of the mass power spectrum from the Lyα forest. We test the full recovery procedure on smoothed particle hydrodynamics (SPH) simulations of three different cosmological models and show that it recovers the true mass power spectrum of the models on comoving scales ~1-10 h-1 Mpc, the upper scale being set by the size of the simulation boxes. The procedure works well even when it is applied to noisy (S/N ~ 10), moderate-resolution (~40 km s-1 pixels) spectra. We present an illustrative application to Songaila & Cowie's Keck HIRES spectrum of Q1422+231; the recovered P(k) is consistent with that of an Ω = 1, h = 0.5, σ8(z = 0) ≈ 0.5 cold dark matter model. The statistical uncertainty in this result is large because it is based on a single QSO, but the method can be applied to large samples of existing QSO spectra and should thereby yield the power spectrum of mass fluctuations on small and intermediate scales at redshifts z ~ 2-4.

The Primeval Mass Fluctuation Spectrum and the Distribution of the Nearby Galaxies

The initial peculiar velocities of tracers of the extragalactic mass distribution computed by a numerical application of the action principle offer a measure of the primeval mass fluctuation power spectrum P(k). Presented here is a method of estimating the spectrum from the fit of the velocity correlation function expressed as an integral over P(k) in linear perturbation theory to the products of pairs of initial velocities of the mass tracers. The method is applied to numerical action solutions for the motions of the galaxies in and near the Local Group. The distributions of products of pairs of the initial velocities are in satisfactory agreement with the predictions from the correlation function. The range of initial separations in the sample is too small to constrain the shape of P(k), but the value is reasonably well determined at wavenumber km ~ 0.4 Mpc–1 in a low-density cosmological model, or km Mpc~ 0.75 Mpc–1 in an Einstein-de Sitter model. In a low-density open or cosmologically flat model, the value of P(km) extrapolated to the present in linear perturbation theory agrees with estimates from the galaxy distribution under the assumption that galaxies trace mass. This adds to the evidence that galaxies are useful mass tracers. In the low-density models, the galaxy distribution near the Local Group grew out of a primeval mass fluctuation δM/M ~ 1 extrapolated to the present in linear theory.

A measurement of the mass fluctuation spectrum from the cluster X-ray temperature function

view Abstract Citations (369) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Measurement of the Mass Fluctuation Spectrum from the Cluster X-Ray Temperature Function Henry, J. Patrick ; Arnaud, Keith A. Abstract We present a statistically complete sample of galaxy clusters which also has complete X-ray temperature information. Using this sample we derive the cluster bolometric luminosity and temperature functions. The temperature function constrains the shape and amplitude of the mass fluctuation power spectrum. For a power law, i.e., with the fluctuation power spectrum proportional to k^n^, we find n = -(1.7^+0.65^_-0.35_), and an amplitude which implies that the rms value of δM/M is 0.59 +/- 0.02 on a scale of 8 h^-1^ Mpc at the present epoch. Publication: The Astrophysical Journal Pub Date: May 1991 DOI: 10.1086/169987 Bibcode: 1991ApJ...372..410H Keywords: Galactic Clusters; Mass Distribution; Mass Spectra; Temperature Distribution; X Ray Astronomy; Computational Astrophysics; Many Body Problem; Power Spectra; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: X-RAYS full text sources ADS | data products SIMBAD (33) NED (24)