Lyman-alpha emission in low-mass compact galaxies with most extreme [OIII]5007/[OII]3727 ratios of above 30

0 Assigned ID: 4125 ----- Attempting Submission 1 (Tue May 23 17:00:18 GMT 2023) ----- HST Phase I Proposal 4125 successfully submitted. Receipt: # 4125-1 ----- Attempting Submission 2 (Wed May 24 04:21:05 GMT 2023) ----- HST Phase I Proposal 4125 successfully submitted. Receipt: # 4125-2 ----- Attempting Submission 3 (Wed May 24 12:50:55 GMT 2023) ----- 0 ----- Attempting Submission 1 (Mon Sep 11 03:46:48 GMT 2023) ----- Lyman-alpha emission in low-mass compact galaxies with most extreme [OIII]5007/[OII]3727 ratios of above 30 Compact and low-mass star-forming galaxies (SFGs) at low redshifts are considered to be the likely nearby counterparts of the high-z star-forming dwarf galaxies thought to be responsible for the reionization of the Universe. We propose to observe with the HST/COS a sample of the five compact SFGs with the highest O32 = [OIII] 5007/[OII] 3727 ratio of 30 - 69 known in the local universe, to obtain medium-resolution spectra of the Ly-alpha emission line. These SFGs were selected from the Data Release 16 of the Sloan Digital Sky Survey to be very compact and to have very young starbursts (EW(Hbeta)>250A). Two SFGs are characterized by the extremely high [OIII]5007/[OII]3727 emission-line ratios of 57 and 69, indicating extreme ionization conditions in their HII regions. The Ly-alpha profiles in those medium resolution spectra will be used to indirectly estimate the escape fraction of the Lyman continuum and will provide important insight on the ISM and radiation field of the star-forming regions. Obtaining the rest-UV spectra of these five SFGs which will serve as templates for the analysis of spectra of high-z dwarf galaxies with active star formation, is thus both urgent and crucial for studies with the JWST and the largest ground-based facilities. The galaxies are faint and satisfy safety conditions for observing with the COS. Furthermore, there are no sources brighter than the COS safety limits in circular regions with the diameter of 43 arcsec centered on the selected galaxies. NUV acquisition images of the targets will be obtained with thestandard Mirror A and the ACQ/IMAGE mode to reach a S/N20 inside a 9x9 pixel box centered on the brightest part of the galaxy. The adopted GALEX NUV magnitudes were used to estimate exposure times. The angular galaxy radius is chosen to be 0.2", inside which most of the galaxy light is concentrated. The total time for acquisition is up to 120s+2x400s=920s per object (HST Primer manual), or third of orbit. As a bonus, the UV morphology of the selected objects will be studied with these images including the low-brightness component of the galaxy. For medium-resolution spectroscopy, the COS in combination with the G130M grating will be used to observe the Ly-alpha line. This resolution is required to resolve the Ly-alpha line profile and to measure features such as the velocity separations between different emission peaks which give the best estimate of the LyC escape fraction. The Ly-alpha emission-line profiles in the spectra of the proposed galaxies will be compared to those in LyC leaking galaxies and in Green Pea galaxies. The GALEX FUV magnitude is used to calculate for each object the required number of orbits to obtain a S/N > 5 for the continuum near Ly-alpha line, in the case of a 100-pixel binned spectrum. This S/N would be enough to obtain the Ly-alpha profile with a sufficient accuracy for radiative transfer modeling and for deriving velocity separations between the peaks. For each target, 0.3 orbit for acquisition, and 3.7 or 4.7 orbits for the spectrum with the medium-resolution G130M grating are needed, totalling 4 or 5 orbits per object. A total of 22 orbits for 5 objects is requested. We do not expect the large impact of reduced-gyro operations on our program because we do not request special orientation requirement for observing of our targets. Data reduction, analysis, and interpretation will be done as in our previous GO 13744, GO 14635, GO 15136, GO 15639, GO 15941 and GO 16271 projects and documented in Izotov et al. (2016a,b, 2018b,c, 2020a, 2021b, 2022). Our team includes experts on all relevant aspects and disposes of all necessary tools, including a custom pipeline for faint COS spectra (Worseck et al. 2011, Syphers et al. 2012), SED fitting tools, Ly-alpha radiation transfer models (Verhamme et al. 2017) and others. All galaxies possess SDSS spectra with which Izotov and Guseva derived data such as nebular line ratios, Hbeta and HeII emission-line luminosities, starburst ages and masses, limits on photoionization by WR stars and shocks, element abundances, specific star formation rates, etc. necessary for interpreting the LyC, and Ly-alpha data. We thus expect to produce scientific results promptly after the data are obtained, as already demonstrated for our successful GO programs 13744, 14635, 15136, 15433, 15639, 15941 and 16271 in papers by Izotov et al. 2016a,b, 2018b,c, 2020a, 2021b, 2022; Schaerer et al 2017, 2018. Galaxies 6 false false true false false false false false SUPPORTED GALAXY DWARF COMPACT EMISSION LINE NEBULA STARBURST NO J2000 J2000 FUV=22.30+/-0.30, NUV=22.59+/-0.43 GALAXY DWARF COMPACT EMISSION LINE NEBULA STARBURST NO J2000 J2000 FUV=20.27+/-0.24, NUV=21.19+/-0.28 GALAXY DWARF COMPACT EMISSION LINE NEBULA STARBURST NO J2000 J2000 FUV=20.50+/-0.10, NUV=20.69+/-0.06 GALAXY DWARF COMPACT EMISSION LINE NEBULA STARBURST NO J2000 J2000 FUV=20.49+/-0.10, NUV=20.61+/-0.15 (No data in Galex database. 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