Comparing Correlation Lengths of Red and Blue Galaxies: A New Standard Length for Testing Cosmic Isotropy

TL;DR

This paper introduces a new empirical method to measure galaxy cluster sizes using correlation lengths of red and blue galaxies, providing a bias-free, precise standard for testing cosmic isotropy and large-scale homogeneity.

Contribution

It presents a novel, bias-free measure of galaxy cluster sizes based on correlation lengths, applicable across redshifts and validated with simulations.

Findings

Correlation length remains nearly constant at ~4.8 Mpc/h up to redshift 0.5.

The method shows excellent agreement between SDSS data and Millennium Simulation.

Provides a new standard for testing cosmic isotropy with high precision.

Abstract

I introduce a simple empirical measure of average galaxy cluster sizes based on a comparison of the correlation lengths of red galaxies with blue that can provide a more accurate and bias-free measure of the average size and number density of galaxy clusters. Using 269,000 galaxies from the SDSS DR6 survey, I show that this 3D correlation length, averaged over many clusters, remains very nearly constant at L0= 4.797 +/- 0.024 Mpc/h from small redshifts out to redshifts of 0.5. This serves as a new measure of cosmic length scales and provides a means of testing the standard cosmological model that is almost free of selection biases. The unprecedented accuracy of the technique allows the possibility of sensitive searches for large-scale inhomogeneities. Applying the same technique to the Millennium Simulation galaxies I find very good agreement between it and the SDSS galaxies.