At the Jet Propulsion Laboratory (JPL) I worked under Jason Rhodes and Hironao Miyatake to investigate assembly bias as a function of brightest cluster galaxy (BCG) ellipticity. The clustering of dark matter halos is enhanced by the underlying dark matter distribution that we do not see, this phenomena is called bias. It has been theoretically shown that bias can depend on other halo properties other than mass, this is known as assembly bias.
I used data 8,648 from the Sloan Digital Sky Survey (SDSS) red-sequence DR8 Matched-filter Probabilistic Percolation (redMaPPer) galaxy clusters. I write Python scripts to extract statistics from the catalog of galaxies and galaxy clusters. After calculating the weak lensing and clustering signals from the data it was found that there was not evidence of assembly bias correlated with BCG ellipticity. This can be graphically shown in the plot below where clustering signals of two subsamples of galaxy clusters are shown. The blue line represents galaxy clusters whose constituent galaxies are far apart, where the green line represents the galaxy clusters whose constituent galaxies are close together. Because the weak clustering signal I calculated between these two subsamples had no significant difference in the different wavelengths of light we sampled: , , , it can be concluded that the underlying dark matter distribution is the same for these two subsamples.
More details about the project can be found in this report I wrote summarizing what I did that summer.