In 1003.4018 Schawinski et al take a sample of morphologically selected Early types from SDSS stripe 82 (deeper imaging), and by eye investigate whether they show signs of major mergers. The fraction of mergers is plotted against three measures of time: u-r colour, Emiisionline classification and post-starburst age.

They want to conclude from this seqence that mergers drive AGN, with a delay time of ~500 Myr and say this is one of very few observational indications of the theoretical understanding of AGN feeding by mergers.