A New Constraint on Reionization from the Evolution of the Ly alpha Luminosity Function at z similar to 6-7 Probed by a Deep Census of z=7.0 Ly alpha Emitter Candidates to 0.3L

作者：Ota Kazuaki^*; Iye Masanori; Kashikawa Nobunari; Konno Akira; Nakata Fumiaki; Totani Tomonori; Kobayashi Masakazu A R; Fudamoto Yoshinobu; Seko Akifumi; Toshikawa Jun; Ichikawa Akie; Shibuya Takatoshi; Onoue Masafusa

来源：Astrophysical Journal, 2017, 844(1): 85.

DOI：10.3847/1538-4357/aa7a0a

• cosmology: observations
• dark ages, reionization, first stars
• galaxies: formation
• galaxies: high-redshift
• galaxies: luminosity function
• mass function

We detect 20 z = 7.0 Ly alpha emitter (LAE) candidates to L(Ly alpha) similar to 2 x 10(42) erg s(-1) or 0.3 L*(z=7) and in a volume of 6.1 x 10(5) Mpc(3) in the Subaru Deep Field and the Subaru/XMM-Newton Deep Survey field by 82 hr and 37 hr of Subaru Suprime-Cam narrowband NB973 and reddest optical y-band imaging. We compare their Ly alpha and UV luminosity functions (LFs) and densities and Ly alpha equivalent widths (EWs) to those of z = 5.7, 6.6, and 7.3 LAEs from previous Suprime-Cam surveys. The Ly alpha LF (density) rapidly declines by a factor of x 1.5 (1.9) in L(Ly alpha) at z = 5.7-6.6 (160 Myr), x1.5 (1.6) at z = 6.6-7.0 (60 Myr) at the faint end, and x2.0 (3.8) at z = 7.0-7.3 (40 Myr). Also, in addition to the systematic decrease in EW at z = 5.7-6.6 previously found, two-thirds of the z = 7.0 LAEs detected in the UV continuum exhibit lower EWs than the z = 6.6 ones. Moreover, while the UV LF and density do not evolve at z = 5.7-6.6, they modestly decline at z = 6.6-7.0, implying galaxy evolution contributing to the decline of the Ly alpha LF. Comparison of the z = 7.0 Ly alpha LF to the one predicted by an LAE evolution model further reveals that galaxy evolution alone cannot explain all of the decline of the Ly alpha LF. If we attribute the discrepancy to Ly alpha attenuation by neutral hydrogen, the intergalactic medium transmission of Ly alpha photons at z = 7.0 would be T-Ly alpha(IGM) <= 0.6-0.7. It is lower (higher) than the T-Ly alpha(IGM) at z = 6.6 (7.3) derived by previous studies, suggesting rapid increase in neutral fraction at z > 6.

• 出版日期2017-7-20
• 单位中国科学院国家天文台