The dynamics of self-interacting dark matter in galaxy clusters

Abstract

This thesis presents three different but connected projects related to the study of the nature of dark matter (DM) using galaxy clusters. In particular, in the first two projects I use cosmological simulations to investigate how DM particles that interact through forces other than gravity affect galaxy clusters as a whole as well as the galaxies that reside inside them.

First, I compared the mass loss of galaxies accreted unto simulated clusters ran with both cold dark matter (CDM) and self-interacting dark matter (SIDM) physics. Due to the additional interactions between the DM haloes of the galaxies and of the clusters, we expect there to be additional mass loss in SIDM galaxies on top of the tidal mass loss due to the gravitational field from the cluster. Indeed, I find that on average not only do SIDM galaxies lose more mass, they are also more susceptible to total disruption.

Second, I investigated the effects of SIDM on major mergers of galaxy clusters. In such events, the gas is offset from the collisionless galaxies due to ram pressure. If the SIDM cross-section is non-zero, the DM can be offset from the galaxies as well. By comparing the offsets of the gas, DM, and stars in simulations ran with different SIDM cross-sections, I found that the DM offset increases with cross-section as expected from analytical models.

The third project was undertaken for the upcoming balloon-borne telescope SuperBIT, whose main science goal will be to map out the DM in and surrounding galaxy clusters. To keep up with SuperBIT's (and any possible successor's) relatively high data rate, we have developed a toolkit of hardware and software that would allow us to physically downlink data mid-flight. I wrote software predicting the trajectories of the system, given the location and time of the release. The system was successfully tested from beginning to end during the SuperBIT 2019 test flight.

In essence, all three projects are based around simulations to predict the trajectories of some form of matter falling into some other form of matter, i.e. DM into clusters, or parachutes into the Earth's atmosphere. The intention was to bring the three projects together and use the SuperBIT hardware that I have helped develop to measure the behaviour of DM and calibrate it against the cosmological simulations. Unfortunately SuperBIT's first science flight was delayed due to the COVID-19 pandemic, and I did not get to measure the DM effects on real astronomical data. I intend to do so in the future.