DescriptionRecently, many isolated dwarf galaxies have been discovered with evidence that their star formation has been impacted by supermassive black hole (SMBH) activity. In light of these new discoveries, we study the effects of SMBH activity on dwarf galaxy evolution within the ROMULUS25 cosmological hydrodynamic simulation. First, we investigate the growth histories of SMBHs and their connection to present-day properties of dwarf galaxies. We show that SMBHs that have grown more than the mean correlate with depleted star-forming gas and suppressed star formation in their host dwarf galaxies in the present day. Dwarf galaxies with under-accreting SMBHs instead exhibit star-forming properties similar to dwarfs entirely without SMBHs. Our work indicates the presence of coeval growth between active, over-grown SMBHs and dwarf galaxies.
In order to understand the relationship between SMBHs and dwarf galaxies, it is important first to find them. However, SMBHs in dwarf galaxies are thought to accrete little and hence exhibit low luminosities. We perform mock observations of the population of SMBHs within dwarf galaxies in ROMULUS25 as a means of identifying SMBHs that may be missed by current observational facilities. We find a large population of SMBHs in dwarfs that are hidden from current x-ray facilities by virtue of their low luminosities, contamination by x-ray-producing processes in the host galaxy, and often large distances from the galaxy center. Our results provide guidance for future x-ray surveys searching for SMBHs in dwarf galaxies.
With the understanding that SMBHs are common in dwarf galaxies and may undergo coeval growth, we turn to understanding the precise mechanisms by which SMBHs may quench star formation in isolated dwarf galaxies. We mock-observe the dwarf galaxies in ROMULUS25 in order to make direct comparisons with recent observations. We find that the fraction of quiescent, isolated dwarf galaxies in ROMULUS25 can be explained by the presence of SMBHs that have had more than average growth. By tracing gas inflows/outflows, gas mass, star formation, and SMBH accretion across time, we find evidence that SMBHs are able to permanently quench star formation in dwarf galaxies. The quenching mechanism varies with the dwarf stellar mass, with the lowest mass dwarfs quenching over many gigayears through slow heating of the interstellar medium. In contrast, the highest mass dwarfs quench rapidly within one gigayear, sweeping gas into the outskirts of the halo. Our results provide a theoretical framework for the new observations of SMBH-driven quenching in isolated dwarf galaxies and may inform future simulations.