TY - JOUR
T1 - Physical properties and H-ionizing-photon production rates of extreme nearby star-forming regions
AU - Chevallard, Jacopo
AU - Charlot, Stéphane
AU - Senchyna, Peter
AU - Stark, Daniel P.
AU - Vidal-García, Alba
AU - Feltre, Anna
AU - Gutkin, Julia
AU - Jones, Tucker
AU - Mainali, Ramesh
AU - Wofford, Aida
N1 - Funding Information:
The authors are grateful to the referee, G. Stasińska, for several comments that significantly improved the paper. JC, SC, and AVG acknowledge support from the European Research Council (ERC) via an Advanced Grant under grant agreement no. 321323-NEOGAL. DPS acknowledges support from the National Science Foundation through the grant AST-1410155. TJ acknowledges support from NASA through Hubble Fellowship grant HST-HF2-51359.001-A awarded by the Space Telescope Science Institute. AF acknowledges support from the ERC via an Advanced Grant under grant agreement no. 339659-MUSICOS. The data described in this pa- per were obtained by the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution, and the NASA/ESA Hubble Space Telescope. Support for HST GO program #14168 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., diunder NASA contract NAS 5-26555.
Publisher Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2018/9/21
Y1 - 2018/9/21
N2 - Measurements of the galaxy UV luminosity function at z ≳ 6 suggest that young stars hosted in low-mass star-forming galaxies produced the bulk of hydrogen-ionizing photons necessary to reionize the intergalactic medium (IGM) by redshift z ∼ 6. Whether star-forming galaxies dominated cosmic reionization, however, also depends on their stellar populations and interstellar medium properties, which set, among other things, the production rate of H-ionizing photons, ξ*ion, and the fraction of these escaping into the IGM. Given the difficulty of constraining with existing observatories the physical properties of z ≳ 6 galaxies, in this work we focus on a sample of 10 nearby objects showing UV spectral features comparable to those observed at z ≳ 6. We use the new-generation BEAGLE tool to model the UV-to-optical photometry and UV/optical emission lines of these local 'analogues' of high-redshift galaxies, finding that our relatively simple, yet fully self-consistent, physical model can successfully reproduce the different observables considered. Our galaxies span a broad range of metallicities and are characterized by high ionization parameters, low dust attenuation, and very young stellar populations. Through our analysis, we derive a novel diagnostic of the production rate of H-ionizing photons per unit UV luminosity, ξ*ion, based on the equivalent width of the bright [O III] λλ4959,5007 line doublet, which does not require measurements of H-recombination lines. This new diagnostic can be used to estimate ξ*ion ion from future direct measurements of the [OIII] λλ4959,5007 line using JWST/NIRSpec (out to z ∼ 9.5), and by exploiting the contamination by H, ß + [O III] λλ4959,5007 of photometric observations of distant galaxies, for instance from existing Spitzer/IRAC data and from future ones with JWST/NIRCam.
AB - Measurements of the galaxy UV luminosity function at z ≳ 6 suggest that young stars hosted in low-mass star-forming galaxies produced the bulk of hydrogen-ionizing photons necessary to reionize the intergalactic medium (IGM) by redshift z ∼ 6. Whether star-forming galaxies dominated cosmic reionization, however, also depends on their stellar populations and interstellar medium properties, which set, among other things, the production rate of H-ionizing photons, ξ*ion, and the fraction of these escaping into the IGM. Given the difficulty of constraining with existing observatories the physical properties of z ≳ 6 galaxies, in this work we focus on a sample of 10 nearby objects showing UV spectral features comparable to those observed at z ≳ 6. We use the new-generation BEAGLE tool to model the UV-to-optical photometry and UV/optical emission lines of these local 'analogues' of high-redshift galaxies, finding that our relatively simple, yet fully self-consistent, physical model can successfully reproduce the different observables considered. Our galaxies span a broad range of metallicities and are characterized by high ionization parameters, low dust attenuation, and very young stellar populations. Through our analysis, we derive a novel diagnostic of the production rate of H-ionizing photons per unit UV luminosity, ξ*ion, based on the equivalent width of the bright [O III] λλ4959,5007 line doublet, which does not require measurements of H-recombination lines. This new diagnostic can be used to estimate ξ*ion ion from future direct measurements of the [OIII] λλ4959,5007 line using JWST/NIRSpec (out to z ∼ 9.5), and by exploiting the contamination by H, ß + [O III] λλ4959,5007 of photometric observations of distant galaxies, for instance from existing Spitzer/IRAC data and from future ones with JWST/NIRCam.
KW - Dark ages
KW - First stars
KW - Galaxies: dwarf
KW - Galaxies: evolution
KW - Galaxies: ism
KW - H ii regions
KW - Methods: data analysis
KW - Reionization
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U2 - 10.1093/mnras/sty1461
DO - 10.1093/mnras/sty1461
M3 - Article
AN - SCOPUS:85051501048
VL - 479
SP - 3264
EP - 3273
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 3
ER -