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Ultraviolet spectra of extreme nearby star-forming regions – approaching a local reference sample for JWST
Author
Senchyna, PeterStark, Daniel P.
Vidal-García, Alba
Chevallard, Jacopo
Charlot, Stéphane
Mainali, Ramesh
Jones, Tucker
Wofford, Aida
Feltre, Anna
Gutkin, Julia
Affiliation
Univ Arizona, Steward ObservIssue Date
2017-12
Metadata
Show full item recordPublisher
OXFORD UNIV PRESSCitation
Ultraviolet spectra of extreme nearby star-forming regions – approaching a local reference sample for JWST 2017, 472 (3):2608 Monthly Notices of the Royal Astronomical SocietyRights
© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.Collection Information
This 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.Abstract
Nearby 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.ISSN
0035-87111365-2966
Version
Final published versionSponsors
NASA 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]Additional Links
http://academic.oup.com/mnras/article/472/3/2608/4082838/Ultraviolet-spectra-of-extreme-nearby-starformingae974a485f413a2113503eed53cd6c53
10.1093/mnras/stx2059