arXiv subjects

S. Zaroubi

Publications and source records attributed to S. Zaroubi.

63 records · Page 4Linked to original sources

arXiv2000

Redshift-Distance Survey of Early-Type Galaxies. IV. Dipoles of the Velocity Field

We use the recently completed redshift-distance survey of nearby early-type galaxies (ENEAR) to measure the dipole component of the peculiar velocity field to a depth of cz ~ 6000 km/s. The sample consists of 1145 galaxies brighter than m_B=14.5 and cz < 7000 km/s, uniformly distributed over the whole sky, and 129 fainter cluster galaxies within the same volume. Most of the Dn-sigma distances were obtained from new spectroscopic and photometric observations conducted by this project, ensuring the homogeneity of the data over the whole sky. These 1274 galaxies are objectively assigned to 696 objects -- 282 groups/clusters and 414 isolated galaxies. We find that within a volume of radius ~ 6000 km/s, the best-fitting bulk flow has an amplitude of |vbulk| =220 +/- 42 km/s in the CMB restframe, pointing towards l=304 +/- 16 degrees, b=25 +/- 11 degrees. The error in the amplitude includes statistical, sampling and possible systematic errors. This solution is in excellent agreement with that obtained by the SFI Tully-Fisher survey. Our results suggest that most of the motion of the Local Group is due to fluctuations within 6000 km/s, in contrast to recent claims of large amplitude bulk motions on larger scales.

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arXiv2000

Large-Scale Power Spectrum and Structures From the ENEAR galaxy Peculiar Velocity Catalog

We estimate the mass density fluctuations power spectrum (PS) on large scales by applying a maximum likelihood technique to the peculiarvelocity data of the recently completed redshift-distance survey of early-type galaxies (ENEAR). The general results are in agreement with the high amplitude power spectra found from similar analysis of other independent all-sky catalogs of peculiar velocity data such as MARK III and SFI. For Lambda & Open CDM COBE normalized PS models, the best-fit parameters are confined by a contour approximately defined by Omega h^{1.3}=0.377+-0.08 and Omega h^{0.88}=0.517+-0.083, respectively. Gamma-shape models, free of COBE normalization, resultsin the weak constraint of $Γ\geq 0.17$ and in the rather stringent constraint of sigma_8 Omega^{0.6}=1.0+-0.25. All quoted uncertainties refer to 3-sigma confidence-level. The calculated PS is used as a prior for Wiener reconstruction of the density field at different resolutions and the three-dimensional velocity field within a volume of radius ~80 Mpc/h. All major structures in the nearby universe are recovered and are well matched to those predicted from all-sky redshift surveys.

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arXiv1999

On the Non-Gaussianity Observed in the COBE-DMR Sky Maps

In this paper we pursue the origin of the non-Gaussianity determined by a bispectrum analysis of the COBE-DMR 4-year sky maps. The robustness of the statistic is demonstrated by the rebinning of the data into 12 coordinate systems. By computing the bispectrum statistic as a function of various data partitions - by channel, frequency, and time interval, we show that the observed non-Gaussian signal is driven by the 53 GHz data. This frequency dependence strongly rejects the hypothesis that the signal is cosmological in origin. A jack-knife analysis of the coadded 53 and 90 GHz sky maps reveals those sky pixels to which the bispectrum statistic is particularly sensitive. We find that by removing data from the 53 GHz sky maps for periods of time during which a known systematic effect perturbs the 31 GHz channels, the amplitudes of the bispectrum coefficients become completely consistent with that expected for a Gaussian sky. We conclude that the non-Gaussian signal detected by the normalised bispectrum statistic in the publicly available DMR sky maps is due to a systematic artifact. The impact of removing the affected data on estimates of the normalisation of simple models of cosmological anisotropy is negligible.

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arXiv1998

Deprojection of Rich Cluster Images

We consider a general method of deprojecting 2D images to reconstruct the 3D structure of the projected object, assuming axial symmetry. The method consists of the application of the Fourier Slice Theorem to the general case where the axis of symmetry is not necessarily perpendicular to the line of sight, and is based on an extrapolation of the image Fourier transform into the so-called cone of ignorance. The method is specifically designed for the deprojection of X-ray, Sunyaev-Zeldovich (SZ) and gravitational lensing maps of rich clusters of galaxies. For known values of the Hubble constant, H0, and inclination angle, the quality of the projection depends on how exact is the extrapolation in the cone of ignorance. In the case where the axis of symmetry is perpendicular to the line of sight and the image is noise-free, the deprojection is exact. Given an assumed value of H0, the inclination angle can be found by matching the deprojected structure out of two different images of a given cluster, e.g., SZ and X-ray maps. However, this solution is degenerate with respect to its dependence on the assumed H0, and a third independent image of the given cluster is needed to determine H0 as well. The application of the deprojection algorithm to upcoming SZ, X-ray and weak lensing projected mass images of clusters will serve to determine the structure of rich clusters, the value of H0, and place constraints on the physics of the intra-cluster gas and its relation to the total mass distribution.

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arXiv1997

Large Scale Power Spectrum from Peculiar Velocities Via Likelihood Analysis

The power spectrum (PS) of mass density fluctuations, independent of `biasing', is estimated from the Mark III catalog of peculiar velocities using Bayesian statistics. A parametric model is assumed for the PS, and the free parameters are determined by maximizing the probability of the model given the data. The method has been tested using detailed mock catalogs. It has been applied to generalized CDM models with and without COBE normalization. The robust result for all the models is a relatively high PS, with $P(k) Ω^{1.2} = (4.8 \pm 1.5) \times 10^3 (Mpc/h)^3$ at $k=0.1 h/Mpc$. An extrapolation to smaller scales using the different CDM models yields $σ_8 Ω^{0.6} = 0.88 \pm 0.15$. The peak is weakly constrained to the range $0.02 \leq k \leq 0.06 h/Mpc$. These results are consistent with a direct computation of the PS (Kolatt & Dekel 1996). When compared to galaxy-density surveys, the implied values for $β$ ($\equiv Ω^{0.6}/b$) are of order unity to within 25%. The parameters of the COBE-normalized, flat CDM model are confined by a 90% likelihood contour of the sort $Ωh_{50}^μn^ν= 0.8 \pm 0.2$, where $μ= 1.3$ and $ν= 3.4, 2.0$ for models with and without tensor fluctuations respectively. For open CDM the powers are $μ= 0.95$ and $ν= 1.4$ (no tensor fluctuations). A $Γ$-shape model free of COBE normalization yields only a weak constraint: $Γ= 0.4 \pm 0.2$.

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arXiv1996

From Local Velocities to Microwave Background

The mass density field as extracted from peculiar velocities in our cosmological neighborhood is mapped back in time to the CMB in two ways. First, the density power spectrum ($P_k$) is translated into a temperature angular power spectrum of sub-degree resolution ($C_l$) and compared to observations. Second, the local density field is translated into a temperature map in a patch on the last-scattering surface of a distant observer. A likelihood analysis of the Mark III peculiar velocity data have constrained the range of parameters for $P_k$ within the family of COBE-normalized CDM models (Zaroubi et al 1996), favoring a slight tilt in the initial spectrum, $n<1$. The corresponding range of $C_l$'s is plotted against current observations, indicating that the CMB data can tighten the constraints further: only models with ``small'' tilt ($n\sim 0.9$) and ``high'' baryonic content ($Ω_b \sim 0.1$) could survive the two data sets simultaneously. The local mass density field that has been recovered from the velocities via a Wiener method is convolved with a Boltzmann calculation to recover $10'$ resolution temperature maps as viewed from different directions. The extent of the CMB patch and the amplitude of fluctuations depend on the choice of cosmological parameters, e.g., the local $100\hmpc$ sphere corresponds to $90'$ to $30'$ at the CMB for $Ω$ between 1 and 0 respectively. The phases of the temperature map are correlated with those of the density field, contrary to the contribution of the Sachs-Wolfe effect alone. This correlation suggests the possibility of an inverse reconstruction of the underlying density field from CMB data with interesting theoretical implications.

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arXiv1996

Large Scale Power Spectrum from Peculiar Velocities Via Likelihood Analysis

The power spectrum (PS) of {\it mass} density fluctuations, independent of ``biasing", is estimated from the Mark3 Catalog of Peculiar Velocities of galaxies using Bayesian statistics. A parametric model is assumed for the PS, and the free parameters are determined by maximizing the posterior probability of the model given the data. The method has been tested using detailed mock catalogs. We use generalized CDM models with and without COBE normalization. The robust result for all the models tested is $P(k) Ω^{1.2} = (4.1 \pm 0.7)x10^3 (Mpc h^{-1})^3$ at $k=0.1 h Mpc^{-1}$, with the peak constrained to the range $0.03 < k < 0.06 h Mpc^{-1}$. It is consistent with a direct computation of the PS (Kolatt \& Dekel 1996). When compared to galaxy-density surveys, the implied values for $β$ ($\equiv Ω^{0.6}/b$) are of order unity to within 25\%. A $Γ$-shape model, free of COBE normalization, is constrained by the velocity data to $Γ=0.5\pm 0.15$ and $σ_8 Ω^{0.6}=0.85\pm 0.1$. Within the family of COBE-normalized CDM models, the best tilted model ($Ω=1$, $n \approx 0.84 h_{50}^{-0.65}$) and the best open model ($n=1$, $Ω\approx 0.75 h_{50}^{-1.0}$) are more likely than the best $Λ$ model ($n=1$, $Λ=1-Ω$, $Ω\approx 0.70 h_{50}^{-1.2}$). The most likely CDM model with $Ω\leq 1$ is found to be of $Ω=1$, $h\approx 0.75$, and a {\it tilted} spectrum of $n= 0.8\pm 0.02$ with tensor fluctuations.The tightest constraint for the tilted-$Λ$ models is of the sort $Ωh_{50}^{1.2} n^ν= 0.7 \pm 0.08$, with $ν=3.8$ and $1.85$ with and without tensor fluctuations respectively.

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arXiv1994

Wiener Reconstruction of The Large Scale Structure

The formalism of Wiener filtering is developed here for the purpose of reconstructing the large scale structure of the universe from noisy, sparse and incomplete data. The method is based on a linear minimum variance solution, given data and an assumed \prior model which specifies the covariance matrix of the field to be reconstructed. While earlier applications of the Wiener filter have focused on estimation, namely suppressing the noise in the measured quantities, we extend the method here to perform both prediction and dynamical reconstruction. The Wiener filter is used to predict the values of unmeasured quantities, such as the density field in un-sampled regions of space, or to deconvolve blurred data. The method is developed, within the context of linear gravitational instability theory, to perform dynamical reconstruction of one field which is dynamically related to some other observed field. This is the case, for example, in the reconstruction of the real space galaxy distribution from its redshift distribution When the field to be reconstructed is a Gaussian random field, such as the primordial perturbation field predicted by the canonical model of cosmology, the Wiener filter can be pushed to its fullest potential. In such a case the Wiener estimator coincides with the Bayesian estimator designed to maximize the {\it posterior} probability. The Wiener filter can be also derived by assuming a quadratic regularization function, in analogy with the `Maximum Entropy' method. The mean field obtained by the minimal variance solution can be supplemented with constrained realizations of the Gaussian field to

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arXiv1993

Wiener Reconstruction of Galaxy Surveys in Spherical Harmonics

The analysis of whole-sky galaxy surveys commonly suffers from the problems of shot-noise and incomplete sky coverage (e.g. at the Zone of Avoidance). The orthogonal set of spherical harmonics is utilized here to expand the observed galaxy distribution. We show that in the framework of Bayesian statistics and Gaussian random fields the $4 π$ harmonics can be recovered and the shot-noise can be removed, giving the most probable picture of the underlying density field. The correction factor from observed to reconstructed harmonics turns out to be the well-known Wiener filter (the ratio of signal to signal+noise), which is also derived by requiring minimum variance. We apply the method to the projected 1.2 Jy IRAS survey. The reconstruction confirms the connectivity of the Supergalactic Plane across the Galactic Plane (at Galactic longitude $l \sim 135^o$ and $l \sim 315^o$) and the Puppis cluster behind the Galactic Plane ($ l \sim 240^o$). The method can be extended to 3-D in both real and redshift space, and applied to other cosmic phenomena such as the COBE Microwave Background maps.

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