A three-dimensional, multi-wavelength view and time-dependent analysis of the Milky Way's local ionized gas

Abstract

This work is the continuation of a series attempting to characterize the local warm ionized medium through both static and time dependent simulations. We build upon our three dimensional, observationally-derived simulation of the local photoionized interstellar medium - based on static photoionization simulations constrained by 3D dust maps - to include metals required to predict collisionally excited optical and infrared emission lines, providing the first all-sky prediction of a series of lines including [SII] 6716$\mathring{A}$, [NII] 6584$\mathring{A}$ and [OIII] 5007$\mathring{A}$. While these predictions only include O-star photoionization under ionization equilibrium, we also carry out a suite of radiation-hydrodynamics simulations including time-dependent metal ionization and the effects of supernova feedback to highlight missing features in our predicted skies. We use the simulations to estimate the very local (1 $\rm kpc^{2}$) Galactic star formation rate, finding a rate of 370 $\rm M_{\odot}~Myr^{-1}~kpc^{-2}$ provides the best match between the observationally-derived and ab-initio simulations. This is approximately a factor of four lower than previous estimates for the star formation rate required to support an observed layer of high-altitude diffuse ionized gas, possibly suggesting a `bursty' star formation history in the region surrounding the Sun. We also investigate the effects of O-star environments on their ability to ionize large volumes of diffuse ionized gas, and find it is likely ionized by a small number of luminous O-stars located in regions where the leakage of their Lyman continuum photons can produce the vast volumes of ionized gas observed in the midplane and at high galactic altitudes.