Testing Homogeneity with Galaxy Star Formation Histories

TL;DR

This study uses galaxy star formation histories from SDSS data to test the large-scale homogeneity of the universe, finding no significant deviations from homogeneity within the analyzed volume and redshift range.

Contribution

It introduces a novel method of probing cosmological homogeneity using galaxy fossil records and star formation histories derived from spectral data.

Findings

No evidence of large-scale inhomogeneity at 95% credibility.

Deviations larger than 5.8% are not supported by the data.

Supports the assumption of cosmological homogeneity at large scales.

Abstract

Observationally confirming spatial homogeneity on sufficiently large cosmological scales is of importance to test one of the underpinning assumptions of cosmology, and is also imperative for correctly interpreting dark energy. A challenging aspect of this is that homogeneity must be probed inside our past lightcone, while observations take place on the lightcone. The star formation history (SFH) in the galaxy fossil record provides a novel way to do this. We calculate the SFH of stacked Luminous Red Galaxy (LRG) spectra obtained from the Sloan Digital Sky Survey. We divide the LRG sample into 12 equal area contiguous sky patches and 10 redshift slices (0.2 < z < 0.5), which correspond to 120 blocks of volume 0.04Gpc3. Using the SFH in a time period which samples the history of the Universe between look-back times 11.5 to 13.4 Gyrs as a proxy for homogeneity, we calculate the posterior distribution for the excess large-scale variance due to inhomogeneity, and find that the most likely solution is no extra variance at all. At 95% credibility, there is no evidence of deviations larger than 5.8%.