1,960 research outputs found
Constraints on galaxy formation theories
The present theories of galaxy formation are reviewed. The relation between peculiar velocities, temperature fluctuations of the microwave background and the correlation function of galaxies point to the possibility that galaxies do not form uniformly everywhere. The velocity data provide strong constraints on the theories even in the case when light does not follow mass of the universe
Nonlinear Behavior of Baryon Acoustic Oscillations from the Zel'dovich Approximation Using a Non-Fourier Perturbation Approach
Baryon acoustic oscillations are an excellent technique to constrain the
properties of dark energy in the Universe. In order to accurately characterize
the dark energy equation of state, we must understand the effects of both the
nonlinearities and redshift space distortions on the location and shape of the
acoustic peak. In this paper, we consider these effects using the Zel'dovich
approximation and a novel approach to 2nd order perturbation theory. The second
order term of the Zel'dovich power spectrum is built from convolutions of the
linear power spectrum with polynomial kernels in Fourier space, suggesting that
the corresponding term of the the Zel'dovich correlation function can be
written as a sum of quadratic products of a broader class of correlation
functions, expressed through simple spherical Bessel transforms of the linear
power spectrum. We show how to systematically perform such a computation. We
explicitly prove that our result is the Fourier transform of the Zel'dovich
power spectrum, and compare our expressions to numerical simulations. Finally,
we highlight the advantages of writing the nonlinear expansion in configuration
space, as this calculation is easily extended to redshift space, and the higher
order terms are mathematically simpler than their Fourier counterparts.Comment: Accepted to ApJ. 7 pages, 2 figure
Effects of Sampling on Measuring Galaxy Count Probabilities
We investigate in detail the effects of sampling on our ability to accurately
reconstruct the distribution of galaxies from galaxy surveys. We use a simple
probability theory approach, Bayesian classifier theory and Bayesian transition
probabilities. We find the best Bayesian estimator for the case of low sampling
rates, and show that even in the optimal case certain higher order
characteristics of the distribution are irretrievably washed out by sparse
sampling: we illustrate this by a simple model for cluster selection. We show
that even choosing an optimal threshold, there are nonzero numbers for both
misidentified clusters and true clusters missed. The introduction of sampling
has an effect on the distribution function that is similar to convolution.
Deconvolution is possible and given in the paper, although it might become
unstable as sampling rates become low. These findings have important
consequences on planning and strategies of future galaxy surveys.Comment: Accepted for publication in ApJ. postscript of 16 pages and three
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