I investigate dwarf galaxies that are initially quenched by reionization, but which resume star formation at least 2 Gyr later. In our simulations,
star formation is restarted in these galaxies when they are struck by a stream of gas, typically either thrown off during a nearby merger (as in the
above gif) or simply hanging off of a neighboring galaxy. If the ram pressure exerted by the stream is within the right range, some of the gas in the
hot halo of the dwarf is compressed onto its disk, forming neutral hydrogen (HI) and, eventually, stars. I am interested in how the gas within dwarf
galaxies evolves and, in particular, the role that environment plays in shaping their gas accretion and star formation histories.
Ultra-diffuse galaxies (UDGs) are galaxies that are both exceptionally large (reff > 1.5 kpc) and exceptionally low surface brightness (μ 0 > 24 mag/arcsec2). Although
originally discovered in clusters, they have also been observed in the field,
which suggests that it is not purely the violence of the cluster environment that creates them. However, it turns out that a galaxy that is isolated now didn't necessarily spend its entire life alone. The field UDGs that form within the Romulus25 cosmological simulation are primarily the products of relatively early major mergers that caused their star formation to migrate outward. I am interested in the properties and origins of these galaxies and other members of the low surface brightness galaxy family.