A Subaru Search for Lyman$\alpha$ Emitters at Redshift 5.7

We present the results of a survey for Ly$\alpha$ emitters at $z\approx 5.7$ based on optical narrow-band (${\lambda }_{\mathrm{c}}=8150$ \AA ~ and $\Delta\lambda = 120$\mathring{A}),andbroad-band($B$,$R_{\rm C}$,$I_{\rm C}$,and$z^\prime$) observations of the field surrounding the high redshift quasar, SDSSp J104433.04$-$012522.2, on the 8.2 m Subaru Telescope with the Subaru Prime Focus Camera, Suprime-Cam. This survey covers a sky area of $\approx 720$ arcmin${}^2$ and a co-moving volume of $\simeq 2\times {10}^5{h}_{0.7}^{-3}$ Mpc${}^3$. We have found 20 candidates of Ly$\alpha$ emitters at $z\approx$ 5.7 with $\mathrm{\Delta }z\approx 0.1$. Two of them have been confirmed star-forming galaxies at $z=5.655$ and $z=5.687$ from our follow-up optical spectroscopy. We discuss star-formation properties of the 20 objects from a statistical point of view. Our survey leads to a new estimate of the star formation rate density at $z\approx 5.7$, $\sim 1.2\times {10}^{-3}{h}_{0.7}{M}_{\odot }$ yr${}^{-1}$ Mpc${}^{-3}$.