First submission -540248356 Assigned ID: 4470 ----- Attempting Submission 1 (Wed May 24 18:12:23 GMT 2023) ----- HST Phase I Proposal 4470 successfully submitted. Receipt: # 4470-1 Resubmitting after running orbit planner and using auto-adjust to update schedulability. -255019688 ----- Attempting Submission 1 (Wed Sep 13 01:31:34 GMT 2023) ----- HST Phase II Proposal 17515 successfully submitted. Receipt: # 17515-1 ----- Attempting Submission 2 (Wed Sep 13 19:06:06 GMT 2023) ----- ----- Attempting Submission 3 (Fri Feb 28 20:58:22 GMT 2025) ----- Chasing Lyman Continuum Leakers in the Local Universe When and how did reionization occur? This will be one of the questions JWST will seek to address in the coming years. The main challenge, however, is the fact that direct measures of the leaking Lyman continuum (LyC) radiation from the same galaxies that reionized the Universe are not possible due to the high opacity of the intergalactic medium (IGM). To fully understand the mechanisms enabling the escape of LyC photons into the IGM, and to uncover the main contributors to the cosmic reionization, it is imperative that we: (1) Test and develop tools to indirectly infer the LyC escape fraction, and (2) compile a sample of nearby LyC leakers allowing us to exploit the ease of fully resolving these objects in the context of LyC escape. We propose a pioneering program to do exactly that. Building on archival observations of eleven local star-forming galaxies (SFGs), we request COS/FUV G130M/1291 spectroscopic data of five additional targets, all of which are expected to have f_esc(LyC)>10% based on cosmological radiation hydrodynamics simulations. Our study will test a much-needed indirect signpost of LyC leakers based primarily on the saturated CII 1334.5A line, allowing us to understand the physical process making LyC leakage possible, and probing the contribution of low-mass SFGs to the epoch of reionization. This HST/COS program observes 5 young star clusters in nearby star-forming galaxies in 5 separate visits with the G130M/1291 COS configuration. Each individual visit acquires the target using the ACQ/IMAGE mode with either MIRROR or MIRRORB. The spectroscopic observations are collected using FP-POS = 3 and 4. These new observations will be complemented by an archival sample of eleven local star-forming galaxies. This sample of 16 nearby star-forming galaxies will allow us to test the much-needed indirect signpost of LyC leakers based primarily on the saturated CII 1334.5A line, allowing us to understand the physical process making LyC leakage possible, and probing the contribution of low-mass SFGs to the epoch of reionization. Target Selection: The new COS sub-sample of star-forming galaxies covers a broad parameter space both in star formation rates, stellar masses, and metallicity. This new COS targets are needed to span the broadest parameter space possible for candidates with the highest probability, P(fesc(LyC)>=10%)> 0.6, to leak Lyman Continuum radiation. The exposure times were calculated assuming the spectrum of a simple stellar population of age 5 or 25 Myr (based on literature values) renormalized to either their WFC3/F275W, or WFC3/F336W magnitudes to reach S/N~10 at 1335 A. The only exception to this approach was VIIZw403. For this target we instead used archival IUE observations to estimate the appropriate exposure times. The members of our team are experts in the field of UV spectroscopy (Dr. Hernandez, Dr. James, Dr. Aloisi, Dr. Mingozzi, Dr. Hirschauer, Dr. Smith, Dr. Jones and Dr. Heckman). The principal investigator Dr. Hernandez is an expert on COS observations having previously served as a Research and Instrument Analyst for the COS instrument team for three years. Her expertise, reflected in her leadership and/or collaboration in at least 14 scientific articles in the last five years, expands from data reduction to scientific projects relying primarily on COS data. Furthermore, her main field of research has focused on chemical abundances of star clusters and the interstellar medium to understand the chemical histories of galaxies at different times. Dr. Aloisi's expertise includes the analysis of spectroscopic observations to obtain column densities and chemical abundances of both the gas, and stellar components in extragalactic environments. One of Dr. Aloisi's primary fields of technical expertise is in UV spectroscopy with space-based telescopes. For years she led the COS+STIS Team, acquiring knowledge on the strengths and weaknesses of the spectrographs. Her experience in both the scientific and technical areas are critical for the success of this project. Dr. James has ample experience with HST/COS spectroscopy as she served as the deputy manager of the COS instrument team. Dr. James has lead several HST/COS observing campaigns to study the environments of nearby star-forming galaxies. Dr. James is also an expert in the derivation of chemical abundances of star-forming galaxies using both UV and optical spectroscopy. Dr. Hirschauer is currently a member of the COS Team with ample experience in data reduction of UV spectroscopic observations. Additionally, Dr. Hirschauer is an expert in star-forming region abundances as it pertains to dwarf galaxies, dust and the mechanisms that facilitate star formation. Dr. Mingozzi is an expert in interstellar medium properties (including outflows, gas-phase abundances, etc), with ample experience analyzing COS spectroscopic observations of star-forming galaxies. Dr. Heckman is an expert in supermassive black holes and the formation and evolution of galaxies. Dr. Heckman is well-known for his work on galactic winds and on the co-evolution of galaxies and supermassive black holes. Dr. Heckman's work is observational with an emphasis on spectroscopy in the ultraviolet and visible. Dr. Heckman first proposed the CII indirect diagnostic of leaking LyC radiation, making his contributions to this program essential. Dr. Smith is an expert on massive stellar populations, the sources producing the energetic LyC photons which eventually reionized the Universe. Dr. Smith has extensive expertise reducing and analyzing UV spectroscopic observations (from both COS and STIS) of stellar populations. Dr. Jones as extensive experience on LyC studies at high redshifts (z~3), having lead several different projects (and publications) searching for LyC candidates. Dr. Jones is also an expert in the analysis of COS observations. 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