0 Your proposal could not be saved. Submission aborted. Assigned ID: 2916 ----- Attempting Submission 1 (Wed Mar 23 22:04:52 GMT 2022) ----- HST Phase I Proposal 2916 successfully submitted. Receipt: # 2916-1 ----- Attempting Submission 2 (Thu Mar 24 16:50:14 GMT 2022) ----- HST Phase I Proposal 2916 successfully submitted. Receipt: # 2916-2 ----- Attempting Submission 3 (Fri Mar 25 13:57:18 GMT 2022) ----- Decades of UV absorption line studies of the Circumgalactic Medium (CGM) of the Milky Way and Magellanic Clouds have revealed crucial information on the physical conditions and distribution of gas surrounding galaxies. However, a precise analysis of these UV absorption line properties requires an accurate understanding of the emerging radiation field from the inner Milky Way, which photoionizes the gas. Currently, the radiation field shape widely used in the literature for these studies is built upon the stellar population surrounding the solar neighborhood. However, recent observations of optical emission lines from the inner Milky Way, towards the same direction as previous HST UV absorption line observations, have revealed clear evidence for significant differences between the local and inner Galaxy radiation fields. In particular, optical emission line ratio observations show that the inner Milky Way is largely ionized and similar to a class of extragalactic systems known as Low Ionization (Nuclear) Emission Regions--LI(N)ERs. We propose to use the inner Milky Way as a bridge to tie extragalactic and Galactic efforts in full Spectral Energy Distribution (SED) models and provide a realistic SED of the inner Milky Way. Our work will provide a more complete understanding of the source of ionization of LI(N)ERs seen in many galaxies, where only optical emission has been previously used as a constraint. In addition, our new SED will provide an accurate representation of the radiation field escaping from Galactic Center and photoionzing gas in the CGM of the Milky Way and Magellanic Couds and is crucial to fully understand the co-evolution of Local Group galaxies. PI Dhanesh Krishnarao is an expert on diffuse ionized gas in galaxies, both within the Milky Way and in extragalactic systems. He has led several papers using optical emission line spectroscopy and UV absorption line spectroscopy to observe and characterize the interstellar medium of galaxies. He is a core member of the Wisconsin H-Alpha Mapper team, and has direct access to the telescope and observing time on it for use in studies of the Milky Way. He is also a member of the Sloan Digital Sky Survey IV and V, where he has extensive experience working with extragalactic observations in the MaNGA survey and has leadership roles in the upcoming SDSS-V as a Data Release Manager for the Local Volume Mapper. PI Krishnarao led the initial discoveries of the ionized Tilted Disk, including towards LS4825, as well as the discovery of optical emission towards the Fermi Bubbles in the direction of PDS 456. Krishnarao also is the first to measure optical emission line ratios towards the inner Milky Way and find that the gas is LI(N)ER like. Krishnarao additionallyled the effort from HST project 16363 (PI D'Onghia), which characterizes the Magellanic CGM and required significant analysis of COS UV spectra and Cloudy photoionization models. PI Krishnarao will lead the analysis of this project alongside CoI Cashman. CoIs Andrew Fox and Frances Cashman are experts in UV absorption-line spectroscopy and has substantial experience investigating the gas cycle in the Milky Way, the Magellanic Clouds, and distant galaxies. Fox has also led numerous HST projects, including HST 12604 entitled "Ionization in the Magellanic Stream: A Case Study of Galactic Accretion" and HST 13840 entitled "The Smith Cloud: Galactic or Extragalactic?". Fox has also developed SED models of the Milky Way radiation field in previous work, but based on local gas and stellar populations. CoI Cashman has considerable experience running Cloudy radiative transfer models, especially time-dependent non-equilibrium model and also has extensive experience in labratory astrophysics with contributions of atomic data used in Cloudy models. Cashman also has experience studying UV absorption line gas towards the inner Milky Way and specifically towards LS4825, where she analyzed HST absorption and FUSE absorption observations to characterize molecular gas in the Tilted Disk and Fermi Bubbles. Stellar Populations and the Interstellar Medium Galaxies 0 Regular false false true true false false SUPPORTED