Speaker
Description
Intermediate mass black holes (IMBHs) remain elusive, in comparison to their supermassive or stellar-mass counterparts, but are essential for understanding galaxy – black hole co-evolution. The small size and distance to IMBHs make dynamic detections difficult, so active galactic nuclei (AGN) signatures provide an easier way to locate IMBHs in dwarf galaxies. Dwarf galaxies also contain other X-ray emitters, such as ultra-luminous X-ray sources (ULXs), that can mimic the signatures expected from dwarf AGN, so distinguishing between the spectral signatures of dwarf AGN and ULXs is notoriously difficult, especially at low metallicities. We present model spectral energy distributions (SEDs) covering 0.01-1.0 Z_solar that include fully self-consistent contributions of IMBHs as a function of metallicity and ULXs as a function of both metallicity and stellar age. Our preliminary analysis shows that at solar metallicity, an AGN contribution of 4% is enough to completely erase any ULX signature at energies >54 eV. Conversely, at low metallicities, ULXs continue to contribute to the ionizing spectrum at >54 eV until the AGN contribution reaches 16%, however, this result is also weakly dependent on stellar age. These results have implications for using emission line diagnostics sensitive to high energy photons, like He II and O I, for separating IMBH and ULX contributions at various metallicities in dwarf galaxies.
