CHORUS II. Subaru/HSC Determination of the Ly$\alpha$ Luminosity
  Function at $z=7.0$: Constraints on Cosmic Reionization Model Parameter
  We present the Ly$\alpha$ luminosity function (LF) derived from 34 Ly$\alpha$
emitters (LAEs) at $z=7.0$ on the sky of $3.1$ deg$^2$, the largest sample
compared to those in the literature obtained at a redshift $z\gtrsim7$. The LAE
sample is made by deep large-area Subaru narrowband observations conducted by
the Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) project. The
$z=7.0$ Ly$\alpha$ LF of our project is consistent with those of the previous
DECam and Subaru studies at the bright and faint ends, respectively, while our
$z=7.0$ Ly$\alpha$ LF has uncertainties significantly smaller than those of the
previous study results. Exploiting the small errors of our measurements, we
investigate the shape of the faint to bright-end Ly$\alpha$ LF. We find that
the $z=7.0$ Ly$\alpha$ LF shape can be explained by the steep slope of $\alpha
\simeq -2.5$ suggested at $z=6.6$, and that there is no clear signature of a
bright-end excess at $z\simeq 7$ claimed by the previous work, which was
thought to be made by the ionized bubbles around bright LAEs whose Ly$\alpha$
photons could easily escape from the partly neutral IGM at $z \simeq 7$. We
estimate the Ly$\alpha$ luminosity densities (LDs) with Ly$\alpha$ LFs at
$z\simeq 6-8$ given by our and the previous studies, and compare the evolution
of the UV-continuum LD estimated with dropouts. The Ly$\alpha$ LD monotonically
decreases from $z\sim 6$ to $8$, and evolves stronger than the UV-continuum LD,
indicative of the Ly$\alpha$ damping wing absorption of the IGM towards the
heart of the reionization epoch.
