Galaxy Formation Theory

My main research is studying how galaxies formed their stars.  Past projects involved reconstructing star formation histories for all observable galaxies as a function of their halo mass and redshift, as well as making empirical connections between galaxies and their host dark matter halos.  At present, I am refining these models to better understand the processes that lead to galaxy quenching.

Phase-space Halo Finding

I am the main developer of the Rockstar (Robust Overdensity Calculation using K-Space Topologically Adaptive Refinement) phase-space halo finder.  Rockstar excels at identifying halos and substructure where other halo finders often fail---in major mergers and at the centers of large clusters. 

Supermassive Black Hole Growth Histories

Methodology for reconstructing galaxy growth histories also applies to black holes.  Quasar luminosity functions combined with AGN occupation fractions and z=0 black hole mass functions provide constraints not only on black hole accretion histories but also on their typical Eddington ratios and duty cycles as a function of redshift and host galaxy mass.

Algorithmic Complexity

On the side, I also like to consider current problems in computer science, especially those with relevance to astrophysical computation.  Recent projects include a faster approach to finding confidence contours (Hierarchical Markov Chain Monte Carlo Methods) as well as improving the computational complexity of calculating Euclidean minimum spanning trees to O(N (log N)^2) or better.