Testing Homogeneity with Galaxy Star Formation Histories
  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%.
