Constraints on the End of Reionization from the Density Fields Surrounding Two Highly Opaque Quasar Sightlines

• Published in: The Astrophysical journal 2021-12, Vol.923 (1), p.87
• Main Authors: Christenson, Holly M., Becker, George D., Furlanetto, Steven R., Davies, Frederick B., Malkan, Matthew A., Zhu, Yongda, Boera, Elisa, Trapp, Adam
• Format: Article
• Language: English
• Subjects: Astronomical models; Astrophysics; Density; Fluctuations; Galaxies; High-redshift galaxies; Hydrogen; Intergalactic media; Intergalactic medium; Ionization; Lyman-alpha galaxies; Opacity; Quasars; Reionization; Scattering; Troughs
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac2a34

The observed large-scale scatter in Ly α opacity of the intergalactic medium at z < 6 implies large fluctuations in the neutral hydrogen fraction that are unexpected long after reionization has ended. A number of models have emerged to explain these fluctuations that make testable predictions for the relationship between Ly α opacity and density. We present selections of z = 5.7 Ly α -emitting galaxies (LAEs) in the fields surrounding two highly opaque quasar sightlines with long Ly α troughs. The fields lie toward the z = 6.0 quasar ULAS J0148+0600, for which we reanalyze previously published results using improved photometric selection, and toward the z = 6.15 quasar SDSS J1250+3130, for which results are presented here for the first time. In both fields, we report a deficit of LAEs within 20 h −1 Mpc of the quasar. The association of highly opaque sightlines with galaxy underdensities in these two fields is consistent with models in which the scatter in Ly α opacity is driven by large-scale fluctuations in the ionizing UV background or by an ultra-late reionization that has not yet concluded at z = 5.7.