Reionization after Planck: The derived growth of the cosmic ionizing emissivity now matches the growth of the galaxy UV luminosity density
- Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands)
- UCO/Lick Observatory, University Of California, Santa Cruz, CA 95064 (United States)
- Department of Astronomy, Yale University, New Haven, CT 06520 (United States)
- Leibniz-Institut fur Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany)
- Department of Physics and Astronomy, South Road, Durham, DH1 3EE (United Kingdom)
- Department of Physics and Astronomy, University of Sussex, Falmer, Brighton, BN1 9QH (United Kingdom)
Thomson optical depth τ measurements from Planck provide new insights into the reionization of the universe. In pursuit of model-independent constraints on the properties of the ionizing sources, we determine the empirical evolution of the cosmic ionizing emissivity. We use a simple two-parameter model to map out the evolution in the emissivity at z ≳ 6 from the new Planck optical depth τ measurements, from the constraints provided by quasar absorption spectra and from the prevalence of Lyα emission in z ∼ 7–8 galaxies. We find the redshift evolution in the emissivity N-dot {sub ion}(z) required by the observations to be (dlog{sub 10} N-dot {sub ion}/dz){sub z=8}=−0.15{sub −0.11}{sup +0.08} ((dlog{sub 10} N-dot {sub ion}/dz){sub z=8}=−0.19{sub −0.11}{sup +0.09} for a flat prior), largely independent of the assumed clumping factor C{sub H ii} and entirely independent of the nature of the ionizing sources. The trend in N-dot {sub ion}(z) is well-matched by the evolution of the galaxy UV-luminosity density (dlog{sub 10}ρ{sub UV}/dz=−0.11±0.04) to a magnitude limit ≳−13 mag, suggesting that galaxies are the sources that drive the reionization of the universe. The role of galaxies is further strengthened by the conversion from the UV luminosity density ρ{sub UV} to N-dot {sub ion}(z) being possible for physically plausible values of the escape fraction f{sub esc}, the Lyman-continuum photon production efficiency ξ{sub ion}, and faint-end cut-off M{sub lim} to the luminosity function. Quasars/active galactic nuclei appear to match neither the redshift evolution nor normalization of the ionizing emissivity. Based on the inferred evolution in the ionizing emissivity, we estimate that the z ∼ 10 UV-Iuminosity density is 8{sub −4}{sup +15}× lower than at z ∼ 6, consistent with the observations. The present approach of contrasting the inferred evolution of the ionizing emissivity with that of the galaxy UV luminosity density adds to the growing observational evidence that faint, star-forming galaxies drive the reionization of the universe.
- OSTI ID:
- 22882521
- Journal Information:
- Astrophysical Journal, Vol. 811, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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