Subaru FOCAS survey of z=7-7.1 Ly{\alpha} emitters: a test for z >~ 7
  Ly{\alpha} photometric luminosity functions
  Recent observations of z >~ 7 Ly{\alpha} emitters (LAEs) have derived a
variety of Ly{\alpha} luminosity functions (LFs) with contradictory results,
evolution or non-evolution from z <~ 6, the epoch after reionization. This
could be because most of z >~ 7 LFs comprise photometric candidates and might
include some contaminations. We conducted the Subaru Telescope Faint Object
Camera And Spectrograph narrowband NB980 ({\lambda}c ~ 9800A, FWHM ~ 100A)
imaging and spectroscopy survey of z=7-7.1 LAEs to compare its
"contamination-free" result with z >~ 7 photometric Ly{\alpha} LFs previously
derived. We imaged the Subaru Deep Field and the sky around a cluster MS
1520.1+3002 and found one LAE candidate, but spectroscopy did not reveal
Ly{\alpha} though deep enough to detect it. We calculated the expected number
of LAEs in our survey, using five z=7 and three z=7.7 Ly{\alpha} LFs from
recent surveys. Seven of them are consistent with null detection
(0.1^{+1.8}_{-0.1}-1.1^{+2.2}_{-1.0} LAEs) within errors including Poisson
statistics and cosmic variance, but average values (0.7-1.1 LAEs) predicted
from one z=7 and two z=7.7 LFs among the seven indicate nearly a single
detection. The remaining one z=7 LF predicts 3.0^{+3.2}_{-2.0} LAEs. As to z=7,
the discrepancy likely comes from different LAE selection criteria. For z=7.7,
there are two possibilities; (1) If z=7.7 LAEs are somehow brighter in
Ly{\alpha} luminosity than lower redshift LAEs, z=7.7 LF is observed to be
similar to or higher than lower redshift LFs even if attenuated by neutral
hydrogen. (2) All/most of the z=7.7 candidates are not LAEs. This supports the
decline of LF from z ~ 6 to 7.7 and reionization at z ~ 6-7.7.
