Physical properties and H-ionizing-photon production rates of extreme nearby star-forming regions
Abstract
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^\star, 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^\star, based on the equivalent width of the bright [O III] λ λ 4959, 5007 line doublet, which does not require measurements of H-recombination lines. This new diagnostic can be used to estimate ξ_ion^\star from future direct measurements of the [O III] λ λ 4959, 5007 line using JWST/NIRSpec (out to z ∼ 9.5), and by exploiting the contamination by H,β +[O {III}] λ λ 4959, 5007 of photometric observations of distant galaxies, for instance from existing Spitzer/IRAC data and from future ones with JWST/NIRCam.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- September 2018
- DOI:
- 10.1093/mnras/sty1461
- arXiv:
- arXiv:1709.03503
- Bibcode:
- 2018MNRAS.479.3264C
- Keywords:
-
- methods: data analysis;
- H <sc>ii</sc> regions;
- galaxies: dwarf;
- galaxies: evolution;
- galaxies: ISM;
- dark ages;
- reionization;
- first stars;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 10 pages, 4 figures, 5 tables, accepted for publication on MNRAS