@article{Environments:2679,
      recid = {2679},
      author = {Mansfield, Philip},
      title = {Dark Matter Halos and Their Environments},
      publisher = {University of Chicago},
      school = {Ph.D.},
      address = {2020-08},
      pages = {249},
      abstract = {The structure and evolution of the universe at large  scales is dominated by dark matter, particularly large  clumps of dark matter called “dark matter halos.” Soon  after running the first large scale, high-resolution  simulations, researchers realized that the growth of these  dark matter halos was closely tied to their surrounding  environment. This connection is called “assembly bias.”  Although this behavior is well-understood for the largest  halos, the cause of assembly bias for smaller dark matter  halos (such as the one which contains our galaxy, the Milky  Way) has remained a mystery for the past fifteen years.  This thesis aims to resolve this mystery through a  synthesis of previous approaches.

Accomplishing this goal  requires constructing a substantial theoretical framework.  One of the leading proposed causes for assembly bias stems  from ambiguity of where halos end and where their  surrounding environment begins. To this end, I develop  Shellfish, the first code which is capable of measuring the  boundary between the two, the “splashback  surface.”

Additionally, the study of assembly bias  requires detailed analysis of large “cosmological” dark  matter simulations. However, despite the long tenure of  these simulations, there remain main unanswered questions  about their accuracy. I perform extensive tests on the  reliability of cosmological simulations, assessing the  reliability of every major property of dark matter halos,  and identifying previously unknown numerical biases which  significantly impact a number of widely-used  simulations.

Finally, using Shellfish to identity halo  boundaries and these numerical tests to ensure reliability,  I tackle the problem of galaxy-mass assembly bias. I  identify the exact halos which are responsible for the  assembly bias signal and use this identification to isolate  the processes which lead to assembly bias. This analysis  shows that galaxy-mass assembly bias is primarily caused by  misidentified “splashback” subhalos, although a modest  fraction of the effect comes from a small number of halos  in massive filaments whose growth is slightly slowed by the  tidal fields of their filaments and by gravitational  heating.},
      url = {http://knowledge.uchicago.edu/record/2679},
      doi = {https://doi.org/10.6082/uchicago.2679},
}