A three-dimensional, multiwavelength 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 [S ii] 6716 Å, [N ii] 6584 Å, and [O iii] 5007 Å. 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 4 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 mid-plane and at high galactic altitudes.