The physical origin for spatially large scatter of IGM opacity at the end of reionization: the IGM Lyα opacity-galaxy density relation

Rikako Ishimoto, Nobunari Kashikawa, Daichi Kashino, Kei Ito, Yongming Liang, Zheng Cai, Takehiro Yoshioka, Katsuya Okoshi, Toru Misawa, Masafusa Onoue, Yoshihiro Takeda, Hisakazu Uchiyama

Submitted on 11 July 2022


The large opacity fluctuations in the z>5.5 Lyα forest may indicate inhomogeneous progress of reionization. To explain the observed large scatter of the effective Lyα optical depth (τeff) of the intergalactic medium (IGM), fluctuation of UV background (Γ model) or the IGM gas temperature (T model) have been proposed, which predict opposite correlations between τeff and galaxy density. In order to address which model can explain the large scatter of τeff, we search for Lyα emitters (LAEs) around two (J1137+3549 and J1602+4228) quasar sightlines with τeff3 and J1630+4012 sightline with τeff5.5. Using a narrowband imaging with Subaru/Hyper Suprime-Cam, we draw LAE density maps to explore their spatial distributions. Overdensities are found within 20 h1Mpc of the quasar sightlines in the low τeff regions, while a deficit of LAEs is found in the high τeff region. Although the τeff of the three quasar sightlines are neither high nor low enough to clearly distinguish the two models, these observed τeff-galaxy density relations all consistently support the Γ model rather than the T model in the three fields, along with the previous studies. The observed overdensities near the low τeff sightlines may suggest that the relic temperature fluctuation does not affect reionization that much. Otherwise, these overdensities could be attributed to other factors besides the reionization process, such as the nature of LAEs as poor tracers of underlying large-scale structures.


Comment: 13 pages, 14 figures, accepted for publication in MNRAS

Subjects: Astrophysics - Astrophysics of Galaxies; Astrophysics - Cosmology and Nongalactic Astrophysics