No Ly α emitters detected around a QSO at z=6.4: Suppressed by the QSO?

Understanding how quasars' (QSOs') ultraviolet (UV) radiation affects galaxy formation is vital to our understanding of the reionization era. Using a custom-made narrow-band filter, NB906, on Subaru/ Suprime-Cam, we investigated the number density of Ly alpha emitters (LAEs) around a QSO at z = 6.4. To date, this is the highest redshift narrow-band observation, where LAEs around a luminous QSO are investigated. Due to the large field of view of Suprime-Cam, our survey area is similar to 5400 cMpc(2), much larger than previous studies at z = 5.7 (similar to 200 cMpc(2)). In this field, we previously found a factor of 7 overdensity of Lyman break galaxies. Based on this, we expected to detect similar to 100 LAEs down to NB906 = 25 ABmag. However, our 6.4 h exposure found none. The obtained upper limit on the number density of LAEs is more than an order lower than the blank fields. Furthermore, this lower density of LAEs spans a large scale of 10 pMpc across. A simple argument suggests that a strong UV radiation from the QSO can suppress star formation in haloes with M-vir < 10(10)M(circle dot) within a pMpc from the QSO, but the deficit at the edge of the field (5 pMpc) remains to be explained.