科研之友
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摘要
Measurements of the galaxy UV luminosity function at z greater than or similar to 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 similar to 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,. xi(star)(ion), and the fraction of these escaping into the IGM. Given the difficulty of constraining with existing observatories the physical properties of z greater than or similar to 6 galaxies, in this work we focus on a sample of 10 nearby objects showing UV spectral features comparable to those observed at z greater than or similar to 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,. xi(star)(ion), based on the equivalent width of the bright [O III] lambda lambda 4959,5007 line doublet, which does not require measurements of H-recombination lines. This new diagnostic can be used to estimate. xi(star)(ion) from future direct measurements of the [OIII] lambda lambda 4959,5007 line using JWST/NIRSpec (out to z similar to 9.5), and by exploiting the contamination by H, ss + [O III] lambda lambda 4959,5007 of photometric observations of distant galaxies, for instance from existing Spitzer/IRAC data and from future ones with JWST/NIRCam.
- 出版日期2018-9
