The Lyα Luminosity Function and Cosmic Reionization at z ∼ 7.0: A Tale of Two LAGER Fields

Abstract

We present the largest-ever sample of 79 Lyα emitters (LAEs) at z ∼ 7.0 selected in the COSMOS and CDFS fields of the LAGER project (the Lyman Alpha Galaxies in the Epoch of Reionization). Our newly amassed ultradeep narrowband exposure and deeper/wider broadband images have more than doubled the number of LAEs in COSMOS, and we have selected 30 LAEs in the second field CDFS. We detect two large-scale LAE-overdense regions in the COSMOS that are likely protoclusters at the highest redshift to date. We perform injection and recovery simulations to derive the sample incompleteness. We show significant incompleteness comes from blending with foreground sources, which however has not been corrected in LAE luminosity functions in the literature. The bright end bump in the Lyα luminosity function in COSMOS is confirmed with 6 (2 newly selected) luminous LAEs (L Lyα > 10 43.3 erg s −1 ). Interestingly, the bump is absent in CDFS, in which only one luminous LAE is detected. Meanwhile, the faint end luminosity functions from the two fields well agree with each other. The 6 luminous LAEs in COSMOS coincide with 2 LAE-overdense regions, while such regions are not seen in CDFS. The bright-end luminosity function bump could be attributed to ionized bubbles in a patchy reionization. It appears associated with cosmic overdensities, thus supports an inside-out reionization topology at z ∼ 7.0, i.e., the high density peaks were ionized earlier compared to the voids. An average neutral hydrogen fraction of x HI ∼ 0.2 -0.4 is derived at z ∼ 7.0 based on the cosmic evolution of the Lyα luminosity function.

The Magellan M2FS Spectroscopic Survey of High-$z$ Galaxies: Lyα Emitters at $z\approx6.6$ and the Evolution of Lyα Luminosity Function over $z\approx5.7-6.6$

“…At higher redshift, the difference between the faint-and bright-end LF evolution increases. The bright-end bump is indeed robustly detected in the Lyα LF at z ∼ 7.0 by the LAGER survey (Zheng et al 2017;Hu et al 2019). They also show that the IGM has a higher x HI at z ∼ 7.0 than at z ≈ 5.7 and 6.6.…”

“…Our LAE sample spans a luminosity range of ∼3 × 10 42 −7 × 10 43 erg s −1 . Previous studies using photometric samples usually assumed that the Lyα line locates at the central wavelength (or effective wavelength) of the narrowband filter due to the lack of the redshift information (e.g., Ouchi et al 2008Ouchi et al , 2010Zheng et al 2017;Shibuya et al 2018;Hu et al 2019). We do the same calculation for comparison and plot the result as the gray line in Figure 7.…”

“…By measuring the evolution of the Lyα luminosity density ρ Lyα , we constrain the neutral hydrogen fraction x HI . We use a method in the literature (e.g., Zheng et al 2017;Konno et al 2018;Hu et al 2019). The density ρ Lyα is related to the UV luminosity density ρ UV by the equation,…”

Fast Luminous Blue Transients in the Reionization Era and Beyond

“…Malhotra & Rhoads 2004;Stark et al 2011;Kashikawa et al 2011), which indicates a neutral IGM during that period. However, this estimation of x HI by the number density of LAEs is affected by the degree of galaxy clustering and tends to be underestimated, because a high degree of galaxy clustering can preferentially ionize these regions (Dijkstra 2014;Hu et al 2019). Therefore, to obtain information of the overall reionization, bright objects whose existence is independent of galaxy clustering are more helpful.…”

HeII Ly$α$ Transmission Spikes and Absorption Troughs in Eight High-resolution Spectra Probing the End of HeII Reionization

“…INTRODUCTION The reionization of intergalactic primordial gas completed separately for hydrogen and helium. For hydrogen, several observational tracers, such as the cosmic microwave background (Planck Collaboration et al 2020), Ly𝛼 emitters (e.g., Mason et al 2018;Hu et al 2019) and Lyman series absorption (e.g., Fan et al 2006), suggest that hydrogen reionization ended at 𝑧 ∼ 6 or even somewhat later (e.g., Becker et al 2015;Kulkarni et al 2019a;Choudhury et al 2021). Due to their similar ionization potential, hydrogen and He I were reionized by soft UV photons that were likely emitted by starforming galaxies (e.g., Madau et al 1999;Faucher-Giguère et al 2008;Eide et al 2020).…”