Reionization after Planck: The Derived Growth of the Cosmic Ionizing Emissivity now matches the Growth of the Galaxy UV Luminosity Density. Bouwens, R. J., Illingworth, G. D., Oesch, P. A., Caruana, J., Holwerda, B., Smit, R., & Wilkins, S. The Astrophysical Journal, 811(2):140, September, 2015. arXiv: 1503.08228
Reionization after Planck: The Derived Growth of the Cosmic Ionizing Emissivity now matches the Growth of the Galaxy UV Luminosity Density [link]Paper  doi  abstract   bibtex   
Thomson optical depth tau measurements from Planck provide new insights into the reionization of the universe. In pursuit of model-independent constraints on the properties of the ionising 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\textgreater\textasciitilde6 from the new Planck optical depth tau measurements, from the constraints provided by quasar absorption spectra and from the prevalence of Ly-alpha emission in z\textasciitilde7-8 galaxies. We find the redshift evolution in the emissivity dot\N\_\ion\(z) required by the observations to be d(log Nion)/dz=-0.15(-0.11)(+0.08), largely independent of the assumed clumping factor C_\HII\ and entirely independent of the nature of the ionising sources. The trend in dot\N\_\ion\(z) is well-matched by the evolution of the galaxy UV-luminosity density (dlog_\10\ rho_UV/dz=-0.11+/-0.04) to a magnitude limit \textgreater\textasciitilde-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 rho_UV to dot(N)_\ion\(z) being possible for physically-plausible values of the escape fraction f_\esc\, the Lyman-continuum photon production efficiency xi_\ion\, and faint-end cut-off \$M_\{lim\}\$ to the luminosity function. Quasars/AGN 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\textasciitilde10 UV-luminosity density is 8(-4)(+15)x lower than at \$z{\textasciitilde}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.
@article{bouwens_reionization_2015,
	title = {Reionization after {Planck}: {The} {Derived} {Growth} of the {Cosmic} {Ionizing} {Emissivity} now matches the {Growth} of the {Galaxy} {UV} {Luminosity} {Density}},
	volume = {811},
	issn = {1538-4357},
	shorttitle = {Reionization after {Planck}},
	url = {http://arxiv.org/abs/1503.08228},
	doi = {10.1088/0004-637X/811/2/140},
	abstract = {Thomson optical depth tau measurements from Planck provide new insights into the reionization of the universe. In pursuit of model-independent constraints on the properties of the ionising 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{\textgreater}{\textasciitilde}6 from the new Planck optical depth tau measurements, from the constraints provided by quasar absorption spectra and from the prevalence of Ly-alpha emission in z{\textasciitilde}7-8 galaxies. We find the redshift evolution in the emissivity dot\{N\}\_\{ion\}(z) required by the observations to be d(log Nion)/dz=-0.15(-0.11)(+0.08), largely independent of the assumed clumping factor C\_\{HII\} and entirely independent of the nature of the ionising sources. The trend in dot\{N\}\_\{ion\}(z) is well-matched by the evolution of the galaxy UV-luminosity density (dlog\_\{10\} rho\_UV/dz=-0.11+/-0.04) to a magnitude limit {\textgreater}{\textasciitilde}-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 rho\_UV to dot(N)\_\{ion\}(z) being possible for physically-plausible values of the escape fraction f\_\{esc\}, the Lyman-continuum photon production efficiency xi\_\{ion\}, and faint-end cut-off \$M\_\{lim\}\$ to the luminosity function. Quasars/AGN 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{\textasciitilde}10 UV-luminosity density is 8(-4)(+15)x lower than at \$z{\textasciitilde}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.},
	number = {2},
	urldate = {2016-05-15},
	journal = {The Astrophysical Journal},
	author = {Bouwens, R. J. and Illingworth, G. D. and Oesch, P. A. and Caruana, J. and Holwerda, B. and Smit, R. and Wilkins, S.},
	month = sep,
	year = {2015},
	note = {arXiv: 1503.08228},
	keywords = {Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics},
	pages = {140},
}

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