arXiv subjects

Idit Zehavi

Publications and source records attributed to Idit Zehavi.

93 records · Page 6Linked to original sources

arXiv1998

Large-Scale Mass Power Spectrum from Peculiar Velocities

The power spectrum of mass density fluctuations is estimated from the Mark III and the SFI catalogs of peculiar velocities by applying a maximum likelihood analysis, using parametric models for the power spectrum and for the errors. Generalized CDM models with and without COBE normalization are used. The applications to the two different data sets give consistent results. The general result is a relatively high amplitude of the power spectrum, eg, at k=0.1 h/Mpc we find P(k) Ω^{1.2} = (4.5+/-2.0)X10^3 (Mpc/h)^3, corresponding to σ_8 Ω^{0.6} = 0.85+/-0.2. Model-dependent constraints on combinations of cosmological parameters are obtained for families of COBE-normalized CDM models. These can roughly be approximated by Ωh_{60}^μn^ν= 0.6+/-0.2, where μ=1.3 and ν=3.7, 2.0 for flat ΛCDM models with and without tensor fluctuations respectively. For open CDM, without tensor fluctuations, the powers are μ=0.9 and ν=1.4. The quoted error-bars reflect the 90% formal likelihood uncertainty for each model and the variance among different models and between catalogs. This is a brief review of a collaborative project (for more details, see Zaroubi et al 1997, Freudling et al 1998). Preliminary constraints in the Ω-Λplane are presented as well.

astro-ph↗

arXiv1998

Large-Scale Mass Power Spectrum from Peculiar Velocities

This is a brief progress report on a long-term collaborative project to measure the power spectrum (PS) of mass density fluctuations from the Mark III and the SFI catalogs of peculiar velocities. The PS is estimated by applying maximum likelihood analysis, using generalized CDM models with and without COBE normalization. The application to both catalogs yields fairly similar results for the PS. The robust result is a relatively high PS, with P(k)Ω^{1.2}=(4.5+/-2.0)X10^3 (Mpc/h)^3 at k=0.1 h/Mpc. An extrapolation to smaller scales using the different CDM models gives σ_8Ω^{0.6}=0.85+/-0.2. The general constraint on the combination of cosmological parameters is of the sort Ω\h_{50}^μ n^ν=0.75+/-0.25, where μ=1.3 and ν=3.7,2.0 for ΛCDM models with and without tensor fluctuations respectively. For open CDM, without tensor fluctuations, the powers are μ=0.9 and ν=1.4.

astro-ph↗

arXiv1998

A Local Hubble Bubble from SNe Ia?

We analyze the monopole in the peculiar velocities of 44 Type Ia supernovae (SNe Ia) to test for a local void. The sample extends from 20 to 300 Mpc/h, with distances, deduced from light-curve shapes, accurate to ~6%. Assuming Omega_m=1 and Omega_lambda=0, the most significant deviation we find from the Hubble law is an outwards flow of (6.6+/-2.2)% inside a sphere of radius 70 Mpc/h as would be produced by a void of ~20% underdensity surrounded by a dense shell. This shell roughly coincides with the local Great Walls. Monte Carlo analyses, using Gaussian errors or bootstrap resampling, show the probability for chance occurrence of this result out of a pure Hubble flow to be ~2%. The monopole could be contaminated by higher moments of the velocity field, especially a quadrupole, which are not properly probed by the current limited sky coverage. The void would be less significant if Omega_m is low and Omega_lambda is high. It would be more significant if one outlier is removed from the sample, or if the size of the void is constrained a-priori. This putative void is not in significant conflict with any of the standard cosmological scenarios. It suggests that the Hubble constant as determined within 70 Mpc/h could be overestimated by ~6% and the local value of Omega may be underestimated by ~20%. While the present evidence for a local void is marginal in this data set, the analysis shows that the accumulation of SNe Ia distances will soon provide useful constraints on elusive and important aspects of regional cosmic dynamics.

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