Escaping Ionizing Radiation in Compact Star-Forming Galaxies: Probing Higher-Mass Systems

0 Assigned ID: 758 ----- Attempting Submission 1 (Fri Apr 05 21:03:39 GMT 2019) ----- 0 ----- Attempting Submission 1 (Fri Jul 19 19:45:22 GMT 2019) ----- Escaping Ionizing Radiation in Compact Star-Forming Galaxies: Probing Higher-Mass Systems Understanding the mechanisms responsible for reionization in the early universe is one of the most important questions in modern extragalactic research. The commonly accepted theory is that star-forming galaxies are the main contributors to this ionizing radiation. However, the exact nature of these galaxies - high mass vs. low mass - is still being debated. Recently, a class of compact starbursting galaxies known as Green Peas have been shown to exhibit high Lyman-alpha and Lyman continuum (LyC) escape fractions. With the existence of a low-redshift population of LyC emitting galaxies confirmed, the research in this field must transition to carrying out comprehensive studies of the nature of LyC emitting galaxies. We propose to use COS to observe 5 compact star-forming galaxies selected from a complete, flux-limited sample that probes to higher galaxy masses than previous studies. This study will significantly expand the number of known LyC emitters and extend their study to include a more diverse range of galaxy properties. We will measure the Lyman-alpha line profiles and attempt to detect LyC emission from these sources. These observations will contribute to our understanding of the escape mechanisms of ionizing radiation in galaxies, as well as provide insight into the types of sources responsible for cosmic reionization. Our targets have a compact/unresolved morphology in the SDSS images (Figure 3) meaning that the 2.5 diameter COS aperture will measure the totality of the galaxy's light so that global quantities can be derived. NUV acquisition images of the targets using excellent input coordinates from SDSS will be obtained with the standard MirrorA and the ACQ/IMAGE mode to reach a S/N~20 inside a 9x9 pixel box centered on the brightest part of the galaxy. The total time needed for acquisition depends on the NUV flux of the object and its compactness. The NUV fluxes for our targets were obtained from the GALEX database. Using the faintest GALEX NUV magnitude in our sample, 21.64 mag, our ETC run using the "Extended source that fills the aperture (1.25 arcsec radius)" setting returned an exposure time of 1200 s. According to Cardamone et al (2009), the angular radius of compact GP-like objects at a redshift of ~0.35 that contains 50% of the UV light is more like 0.3 arcsec. This implies that a much shorter integration time of 300 s will still yield an image with a high S/N in excess of 20. As a bonus we will be able to study the morphology of our targets with these acquisition images. We plan to use COS in combination with two gratings: 1) the low-resolution G140L grating (770-1950 A) to measure the LyC. We adopt a flat spectral energy distribution and use the GALEX NUV magnitude in order to calculate the required number of orbits to probe the LyC escape fraction down to 2% with SNR ~2-3. 2) the medium-resolution G160M grating (1602-1772 A) to observe the Ly-alpha line. Again, we adopt a flat spectral energy distribution and use the GALEX NUV magnitude as well as inputting a model Ly-alpha emission line to calculate for each object the required exposure time to obtain a S/N >5. We check the later estimate by using our measured H-alpha line fluxes, and assume Case B recombination and a 5% Ly-alpha escape fraction to arrive at an alternate exposure time estimate. Since most of our sources exhibit negligible absorption based on their optical spectra (c_(Hbeta) ~0), we simply adopt Galactic extinction, which is ~0.05 mag for these galaxies, in the ETC calculations. The ETC shows our count rates are safe for the instrument for all of our targets. Samantha Brunker is working on her PhD thesis which is primarily focused on the compact extreme star-forming galaxies rom the KISS and H-alpha Dots [O III]-selected samples described in this proposal. She is studying the global properties of these objects, specifically their environments, metallicities, and their star formation rates. Dr. Aparna Venkatesan is an expert on the theoretical modeling and understanding of how ionizing radiation is produced in and escapes from these compact star-forming Green Pea-like galaxies. Dr. Danielle Berg is an expert in observing with COS and reducing and processing COS spectral data. She is also an expert in measuring nebular abundances for star forming galaxies. Dr. John Salzer is an expert in survey design and implementation targeting emission line sources. He is an expert in measuring nebular abundances for star forming galaxies. Galaxies and the IGM Cosmology 6 false false true false false false false SUPPORTED GALAXY STARBURST NO This object is compact. The coordinates were obtained from SDSS DR15. NUV and FUV magnitudes come from GALEX, and gri magnitudes come from SDSS DR15. J2000 J2000 NUV=22.08 +/- 0.25, FUV=22.27, g=21.62, r=21.12, i=22.13 GALAXY STARBURST NO This object is compact. The coordinates were obtained from SDSS DR15. NUV and FUV magnitudes come from GALEX, and gri magnitudes come from SDSS DR15. J2000 J2000 NUV=19.67 +/- 0.03, FUV=20.66, g=19.47, r=18.96, i=19.59 GALAXY STARBURST NO This object is compact. The coordinates were obtained from SDSS DR15. NUV magnitude comes from GALEX, and gri magnitudes come from SDSS DR15. J2000 J2000 NUV=21.64 +/- 0.31, g=21.04, r=20.98, i=20.25 GALAXY STARBURST NO This object is compact. The coordinates were obtained from SDSS DR15. NUV and FUV magnitudes come from GALEX, and gri magnitudes come from SDSS DR15. J2000 J2000 NUV=21.14 +/- 0.08, FUV=21.25, g=20.92, r=20.66, i=20.96 GALAXY STARBURST NO This object is compact. The coordinates were obtained from SDSS DR15. NUV and FUV magnitudes come from GALEX, and gri magnitudes come from SDSS DR15. J2000 J2000 NUV=21.59 +/- 0.34, FUV=21.91, g=21.31, r=20.50, i=21.61 COS/NUV Imaging No No MIRRORA COS/FUV Spectroscopic No No G160M 1600 COS/FUV Spectroscopic No No G140L 800 COS/NUV Imaging No No MIRRORA COS/FUV Spectroscopic No No G160M 1589 COS/FUV Spectroscopic No No G140L 800 COS/NUV Imaging No No MIRRORA COS/FUV Spectroscopic No No G160M 1611 COS/FUV Spectroscopic No No G140L 800 COS/NUV Imaging No No MIRRORA COS/FUV Spectroscopic No No G160M 1600 COS/FUV Spectroscopic No No G140L 800 COS/NUV Imaging No No MIRRORA COS/FUV Spectroscopic No No G160M 1589 COS/FUV Spectroscopic No No G140L 800 1562951762940 /Users/sbrunker/Documents/Research_wJohn/HST_proposal_Cycle27/phase2/OP-cache/hst_uv_c27_phase2-v01.xml The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. 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