To investigate the growth and evolution of the earliest structures in the Universe, we identify more than 200 galaxy overdensities in the Candidate Cluster and Protocluster Catalog (CCPC). This compilation is produced by mining open astronomy data sets for over-densities of high redshift galaxies that are spectroscopically confirmed. At these redshifts, the Universe is only a few billion years old. This data mining approach yields a nearly 10 fold increase in the number of known protoclusters in the literature. The CCPC also includes the highest redshift, spectroscopically confirmed protocluster at z=6.56. For nearly 1500 galaxies contained in the CCPC between redshifts of 2.0<z<6.6, we find archival Spitzer images at 3.6 and 4.5μm bandpasses. These Spitzer wavelengths serve as a proxy measurement for the stellar mass of the galaxies. The galaxies in protoclusters appear to be consistent with a passively evolving, older stellar population. We find no statistically significant difference between protocluster and field galaxy populations. Galaxy formation models suggest that galaxies in dense environments should be more massive. Comparing the Schechter function fits to the data at different epochs provides an evolutionary track for how protocluster galaxies evolve. We compare the data to the predictions of a large-scale simulation, the Millennium Run. We analyze the simulated data with the same suite of algorithms and metrics as in the CCPC. The results of this exercise yield a number of significant discrepancies between the theoretical predictions and what is seen. The universe contains a much larger density of bright galaxies than what the model predicts. At z>2, the brightest galaxies are older and more massive than anticipated by the model.
- Pub Date:
- January 2018