Puzzles in Galaxy Evolution
Charles Louis Steinhardt
Niels Bohr Institute



I will describe a pair of sharp puzzles suggesting a possible mismatch between our theory of galaxy evolution and recent observations. First, current models predict that the z ~ 4-8 universe should be a time in which the most massive galaxies are transitioning from their initial halo assembly to the later baryonic evolution seen in star-forming galaxies and quasars. Instead, massive galaxies appear to exist impossibly early, before their halos should even have been able to assemble. Second, there is increasing observational evidence that history of many galaxies may not be driven by environment but rather by cosmic factors. I will then discuss whether theory and observation are truly inconsistent or whether analytical techniques might be responsible for the current tension. I will also outline a possible theoretical solution, and describe how upcoming surveys (including BUFFALO, an expanded version of the HST Frontier Fields, and future JWST studies) might be able to test it.