Local Group velocity versus gravity: the coherence function

Abstract

In maximum-likelihood analyses of the Local Group (LG) acceleration, the object describing nonlinear effects is the coherence function (CF), i.e. the cross-correlation coefficient of the Fourier modes of the velocity and gravity fields. We study the CF both analytically, using perturbation theory, and numerically, using a hydrodynamic code. The dependence of the function on Omega_m and the shape of the power spectrum is very weak. The only cosmological parameter that the CF is strongly sensitive to is the normalization sigma_8 of the underlying density field. Perturbative approximation for the function turns out to be accurate as long as sigma_8 is smaller than about 0.3. For higher normalizations we provide an analytical fit for the CF as a function of sigma_8 and the wavevector. The characteristic decoherence scale which our formula predicts is an order of magnitude smaller than that determined by Strauss et al. This implies that present likelihood constraints on cosmological parameters from analyses of the LG acceleration are significantly tighter than hitherto reported.

9 pages, 8 figures, uses mn2e.cls; a revised version, accepted in MNRAS

References in corpus (7)

• Non-Linear Evolution of the Bispectrum of Cosmological Perturbations
• The IRAS PSCz Dipole
• Likelihood Analysis of the Local Group Acceleration
• The Power Spectrum of the PSC Redshift Survey
• The $\Omega$ Dependence in the Equations of Motion
• Reconstructing Cosmic Peculiar Velocities from the Mildly Nonlinear Density Field
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• Not a Copernican observer: biased peculiar velocity statistics in the local Universe
• Likelihood analysis of the Local Group acceleration revisited
• Uneven flows: On cosmic bulk flows, local observers, and gravity
• Towards the optimal window for the 2MASS dipole
• Motion of the Local Group as a cosmological probe