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dc.contributor.authorSenchyna, Peter
dc.contributor.authorStark, Daniel P.
dc.contributor.authorVidal-García, Alba
dc.contributor.authorChevallard, Jacopo
dc.contributor.authorCharlot, Stéphane
dc.contributor.authorMainali, Ramesh
dc.contributor.authorJones, Tucker
dc.contributor.authorWofford, Aida
dc.contributor.authorFeltre, Anna
dc.contributor.authorGutkin, Julia
dc.date.accessioned2017-11-03T21:27:33Z
dc.date.available2017-11-03T21:27:33Z
dc.date.issued2017-12
dc.identifier.citationUltraviolet spectra of extreme nearby star-forming regions – approaching a local reference sample for JWST 2017, 472 (3):2608 Monthly Notices of the Royal Astronomical Societyen
dc.identifier.issn0035-8711
dc.identifier.issn1365-2966
dc.identifier.doi10.1093/mnras/stx2059
dc.identifier.urihttp://hdl.handle.net/10150/625962
dc.description.abstractNearby dwarf galaxies provide a unique laboratory in which to test stellar population models below Z(circle dot)/2. Such tests are particularly important for interpreting the surprising high-ionization ultraviolet (UV) line emission detected at z > 6 in recent years. We present HST/COS UV spectra of 10 nearby metal-poor star-forming galaxies selected to show He II emission in SDSS optical spectra. The targets span nearly a dex in gas-phase oxygen abundance (7.8 < 12 + logO/H < 8.5) and present uniformly large specific star formation rates (sSFR similar to 10(2) Gyr(-1)). The UV spectra confirm that metal-poor stellar populations can power extreme nebular emission in high-ionization UV lines, reaching CIII] equivalent widths comparable to those seen in systems at z similar to 6-7. Our data reveal a marked transition in UV spectral properties with decreasing metallicity, with systems below 12 + logO/H less than or similar to 8.0 (Z/Z(circle dot) less than or similar to 1/5) presenting minimal stellar wind features and prominent nebular emission in He II and C IV. This is consistent with nearly an order of magnitude increase in ionizing photon production beyond the He+-ionizing edge relative to H-ionizing flux as metallicity decreases below a fifth solar, well in excess of standard stellar population synthesis predictions. Our results suggest that often-neglected sources of energetic radiation such as stripped binary products and very massive O-stars produce a sharper change in the ionizing spectrum with decreasing metallicity than expected. Consequently, nebular emission in C IV and He II powered by these stars may provide useful metallicity constraints in the reionization era.
dc.description.sponsorshipNASA through Space Telescope Science Institute [14168]; NASA [NAS 5-26555]; W.M. Keck Foundation; National Science Foundation [AST-1410155]; European Research Council [321323-NEOGAL]; NASA through Hubble Fellowship - Space Telescope Science Institute [HST-HF2-51359.001-A]; ERC [339659-MUSICOS]en
dc.language.isoenen
dc.publisherOXFORD UNIV PRESSen
dc.relation.urlhttp://academic.oup.com/mnras/article/472/3/2608/4082838/Ultraviolet-spectra-of-extreme-nearby-starformingen
dc.rights© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.en
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/
dc.subjectstars: massiveen
dc.subjectgalaxies: evolutionen
dc.subjectgalaxies: stellar contenten
dc.subjectultraviolet: galaxiesen
dc.titleUltraviolet spectra of extreme nearby star-forming regions – approaching a local reference sample for JWSTen
dc.typeArticleen
dc.contributor.departmentUniv Arizona, Steward Observen
dc.identifier.journalMonthly Notices of the Royal Astronomical Societyen
dc.description.collectioninformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.en
dc.eprint.versionFinal published versionen
refterms.dateFOA2018-09-11T23:54:50Z
html.description.abstractNearby dwarf galaxies provide a unique laboratory in which to test stellar population models below Z(circle dot)/2. Such tests are particularly important for interpreting the surprising high-ionization ultraviolet (UV) line emission detected at z > 6 in recent years. We present HST/COS UV spectra of 10 nearby metal-poor star-forming galaxies selected to show He II emission in SDSS optical spectra. The targets span nearly a dex in gas-phase oxygen abundance (7.8 < 12 + logO/H < 8.5) and present uniformly large specific star formation rates (sSFR similar to 10(2) Gyr(-1)). The UV spectra confirm that metal-poor stellar populations can power extreme nebular emission in high-ionization UV lines, reaching CIII] equivalent widths comparable to those seen in systems at z similar to 6-7. Our data reveal a marked transition in UV spectral properties with decreasing metallicity, with systems below 12 + logO/H less than or similar to 8.0 (Z/Z(circle dot) less than or similar to 1/5) presenting minimal stellar wind features and prominent nebular emission in He II and C IV. This is consistent with nearly an order of magnitude increase in ionizing photon production beyond the He+-ionizing edge relative to H-ionizing flux as metallicity decreases below a fifth solar, well in excess of standard stellar population synthesis predictions. Our results suggest that often-neglected sources of energetic radiation such as stripped binary products and very massive O-stars produce a sharper change in the ionizing spectrum with decreasing metallicity than expected. Consequently, nebular emission in C IV and He II powered by these stars may provide useful metallicity constraints in the reionization era.


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