Research Activities

I study the structure of the dark matter halos that are believed to host some of the earliest galaxies and supermassive black holes. I am interested in how the first galaxies formed, and what physical processes are relevant. This includes feedback from Population III stars, feedback from the precursors to supermassive black holes, and any systematic effects from the dark matter halo properties. The last possibility has been the major emphasis of my Ph.D. thesis

I use N-body simulations (using GADGET-2) to trace growth of dark matter halos from early times down to a redshift of z=6, allowing us to follow the halos from z=20 when the metal free Population III stars form until the earliest quasars are shining at z=6. I first studied the growth of angular momentum, in Davis and Natarajan (2009). We found that, similar to low redshift halos, the spin distribution of our halo sample is log-normal. We also found that high spin and low spin halos show a difference in clustering strength: high spin halos are more strongly clustered. Therefore, high spin halos will have a stronger feedback effects on their neighbors, as their neighbors are closer on average.

We then turned to the internal structure of these halos in Davis and Natarajan (2010). We measured the halo shape, concentration, and circular velocity, and the bias in the correlation function when haloes were binned by these criterion. We also found a systematic offset in the peak of the circular velocity curves for high and low spin halos of the same mass.

My most recent work has been studying the virial state of our halo sample (Davis, D'Aloisio, and Natarajan 2010). We find that even after including the surface terms from the virial equation, high redshift dark matter halos have too much kinetic energy on average. This will also have an effect on the baryonic structures forming in these halos.