Zusammenfassung
Understanding how QSO's UV radiation affects galaxy formation is vital to our
understanding of reionization era. Using a custom made narrow-band filter,
$NB906$, on Subaru/Suprime-Cam, we investigated the number density of
Ly$\alpha$ emitters (LAE) 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
$\sim$5400~cMpc$^2$, much larger than previously studies at z=5.7 ($\sim$200
cMpc$^2$). In this field, we previously found a factor of 7 overdensity of
Lyman break galaxies (LBGs). Based on this, we expected to detect $\sim$100
LAEs down to $NB906$=25 ABmag. However, our 6.4 hour 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 $p$Mpc across. A simple argument suggests a strong UV radiation
from the QSO can suppress star-formation in halos with
$M_vir<10^10M_ødot$ within a $p$Mpc from the QSO, but the deficit at the
edge of the field (5 $p$Mpc) remains to be explained.
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