%0 Generic %1 naidu2019rapid %A Naidu, Rohan P. %A Tacchella, Sandro %A Mason, Charlotte A. %A Bose, Sownak %A Oesch, Pascal A. %A Conroy, Charlie %D 2019 %K library %T Rapid Reionization by the Oligarchs: The Case for Massive, UV-Bright, Star-Forming Galaxies with High Escape Fractions %U http://arxiv.org/abs/1907.13130 %X The protagonists of cosmic reionization remain elusive. Faint star-forming galaxies are leading candidates because they are numerous and may have significant ionizing photon escape fractions ($f_esc$). Here we update this picture via an empirical model that successfully predicts latest observations (e.g., the drop in star-formation density at z>8). We generate an ionizing spectrum for each galaxy in our model and constrain $f_esc$ using latest measurements of the reionization timeline (e.g., Ly$\alpha$ damping of quasars and galaxies at z>7). Assuming a constant $f_esc$, we find $M_UV$<-13.5 galaxies need $f_esc=0.21^+0.06_-0.04$ to complete reionization. The inferred IGM neutral fraction is 0.9, 0.5, 0.1 at z=8.2, 6.8, 6.2$\pm$0.2, i.e., the bulk of reionization transpires in 300 Myrs. Inspired by the emergent sample of Lyman Continuum (LyC) leakers that overwhelmingly displays higher-than-average star-formation surface density ($\Sigma$), we propose a model relating $f_esc$ to $\Sigma$ and find $f_esc\propto\Sigma^0.4\pm0.1$. Since $\Sigma$ falls by ~2.5 dex between z=8 and z=0, our model explains the humble upper limits on $f_esc$ at lower redshifts and its required evolution to ~0.2 at z>6. Within this model, strikingly, <5% of galaxies with $M_UV$<-18 (the `oligarchs') account for >80% of the reionization budget. In fact, faint sources ($M_UV$>-16) must be relegated to a limited role to ensure high neutral fractions at z=7-8. Shallow faint-end slopes of the UV luminosity function ($\alpha$>-2) and/or $f_esc$ distributions skewed toward bright galaxies produce the required late and rapid reionization. We predict LyC leakers like COLA1 (z=6.6, $f_esc$~30%, $M_UV$=-21.5) become increasingly common towards z~6 and that the drivers of reionization do not lie hidden across the faint-end of the luminosity function, but are already known to us. (abridged)

@misc{naidu2019rapid, abstract = {The protagonists of cosmic reionization remain elusive. Faint star-forming galaxies are leading candidates because they are numerous and may have significant ionizing photon escape fractions ($f_{esc}$). Here we update this picture via an empirical model that successfully predicts latest observations (e.g., the drop in star-formation density at z>8). We generate an ionizing spectrum for each galaxy in our model and constrain $f_{esc}$ using latest measurements of the reionization timeline (e.g., Ly$\alpha$ damping of quasars and galaxies at z>7). Assuming a constant $f_{esc}$, we find $M_{UV}$<-13.5 galaxies need $f_{esc}=0.21^{+0.06}_{-0.04}$ to complete reionization. The inferred IGM neutral fraction is [0.9, 0.5, 0.1] at z=[8.2, 6.8, 6.2]$\pm$0.2, i.e., the bulk of reionization transpires in 300 Myrs. Inspired by the emergent sample of Lyman Continuum (LyC) leakers that overwhelmingly displays higher-than-average star-formation surface density ($\Sigma$), we propose a model relating $f_{esc}$ to $\Sigma$ and find $f_{esc}\propto\Sigma^{0.4\pm0.1}$. Since $\Sigma$ falls by ~2.5 dex between z=8 and z=0, our model explains the humble upper limits on $f_{esc}$ at lower redshifts and its required evolution to ~0.2 at z>6. Within this model, strikingly, <5% of galaxies with $M_{UV}$<-18 (the `oligarchs') account for >80% of the reionization budget. In fact, faint sources ($M_{UV}$>-16) must be relegated to a limited role to ensure high neutral fractions at z=7-8. Shallow faint-end slopes of the UV luminosity function ($\alpha$>-2) and/or $f_{esc}$ distributions skewed toward bright galaxies produce the required late and rapid reionization. We predict LyC leakers like COLA1 (z=6.6, $f_{esc}$~30%, $M_{UV}$=-21.5) become increasingly common towards z~6 and that the drivers of reionization do not lie hidden across the faint-end of the luminosity function, but are already known to us. (abridged)}, added-at = {2019-08-01T04:51:00.000+0200}, author = {Naidu, Rohan P. and Tacchella, Sandro and Mason, Charlotte A. and Bose, Sownak and Oesch, Pascal A. and Conroy, Charlie}, biburl = {https://www.bibsonomy.org/bibtex/2df7da8a29419d7a1480f3edb83165ccf/gpkulkarni}, description = {Rapid Reionization by the Oligarchs: The Case for Massive, UV-Bright, Star-Forming Galaxies with High Escape Fractions}, interhash = {22723d5454b21bfb0cb10efa27a5cf4f}, intrahash = {df7da8a29419d7a1480f3edb83165ccf}, keywords = {library}, note = {cite arxiv:1907.13130Comment: Submitted to ApJ. Figure 5 features a compilation of LyC leakers and (hopefully) motivates an $f_{esc}$-$\Sigma_{SFR}$ connection. Figures 8, 9, and Table 1 profile the "oligarchs". Figure 10 compares with "democratic" reionization. Comments very welcome!}, timestamp = {2019-08-01T04:51:00.000+0200}, title = {Rapid Reionization by the Oligarchs: The Case for Massive, UV-Bright, Star-Forming Galaxies with High Escape Fractions}, url = {http://arxiv.org/abs/1907.13130}, year = 2019 }