Garofali, KristenBasu-Zych, AntaraJohnson, Benjamin D.Tzanavaris, PanayiotisJaskot, AnneRichardson, ChrisLehmer, Bret D.Yukita, MihokoHodges-Kluck, EdmundHornschemeier, AnnPtak, AndrewVulic, Neven2023-07-182023-07-182023-06-30https://doi.org/10.48550/arXiv.2307.00050http://hdl.handle.net/11603/28755We present a methodology for modeling the joint ionizing impact due to a ``simple X-ray population" (SXP) and its corresponding simple stellar population (SSP), where ``simple" refers to a single age and metallicity population. We construct composite spectral energy distributions (SEDs) including contributions from ultra-luminous X-ray sources (ULXs) and stars, with physically meaningful and consistent consideration of the relative contributions of each component as a function of instantaneous burst age and stellar metallicity. These composite SEDs are used as input for photoionization modeling with Cloudy, from which we produce a grid for the time- and metallicity-dependent nebular emission from these composite populations. We make the results from the photoionization simulations publicly available. We find that the addition of the SXP prolongs the high-energy ionizing output from the population, and correspondingly increases the intensity of nebular lines such as He II λ1640,4686, [Ne V] λ3426,14.3μm, and [O IV] 25.9μm by factors of at least two relative to models without an SXP spectral component. This effect is most pronounced for instantaneous bursts of star formation on timescales > 10 Myr and at low metallicities (∼ 0.1 Z⊙), due to the imposed time- and metallicity-dependent behavior of the SXP relative to the SSP. We propose nebular emission line diagnostics accessible with JWST suitable for inferring the presence of a composite SXP + SSP, and discuss how the ionization signatures compare to models for sources such as intermediate mass black holes.46 pagesen-USThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.Public Domain Mark 1.0http://creativecommons.org/publicdomain/mark/1.0/Text