Speaker
Description
Nebular He II λ4686 in low-metallicity star-forming galaxies requires a hard ionizing spectrum beyond that produced by stellar populations. I present new deep Chandra and XMM-Newton observations that quantify the relative contributions of ULXs and hot diffuse plasma to this ionizing field in nearby metal-poor starbursts. Chandra’s sub-arcsecond imaging resolves individual ULXs, deconfuses them from surrounding emission, and establishes their spatial association with young stellar clusters. XMM-Newton constrains the soft X-ray luminosity and temperature structure of the diffuse thermal plasma component. Combining spatially resolved X-ray spectroscopy with photoionization modeling, I derive the relative contributions of ULXs, hot gas, and young stellar populations to the photon budget required to power nebular He II and related high-ionization tracers. These observations provide empirical constraints on the emergent ionizing spectra of super-Eddington compact-object populations in metal-poor environments. These results define the observational framework within which NewAthena’s increased throughput and high-resolution spectroscopy will enable population-level constraints on super-Eddington accretion and its coupling to the surrounding medium in metal-poor galaxies.
