Lyα Emitters at z = 5.7 in the Subaru Deep Field

Abstract We present the properties of Ly emitters (LAEs) at z=5. 7 in the Subaru Deep Field. A photometric sample of 89 LAE candidates was constructed from narrow-band data down to NB816 = 26. 0 (AB) in a continuous 725 \, arcmin² area. Spectra of 39 objects satisfying the photometric selection criteria for LAEs were obtained with Subaru and Keck II Telescopes, among which 28 were confirmed LAEs, one was a nearby galaxy, and eight were unclassified. We also obtained spectra of another 24 NB816-excess objects in the field, identifying six additional LAEs. We find that the Ly luminosity function derived from the photometric sample is reproduced well by a Schechter function with L^ = 7. 9^+3. 0-₂. ₂ 10^42 \, erg \, s^-1 and ^ = 6. 3^+3. 0-₂. ₀ 10^-4 \, Mpc^-3 for =-1. 5 (fixed) over the whole luminosity range of L 3 10^42 -- 3 10^43 \, erg \, s^-1. We then measured the rest-frame Ly equivalent widths for the confirmed LAEs, to find that the median among the 28 objects satisfying the photometric selection criteria is W₀^i = 233 \, Å. We infer that 30%-40% of LAEs at z=5. 7 exceed W₀^i = 240 \, Å. These large-EW objects probably cannot be accounted for by ordinary star-forming populations with a Salpeter IMF. We also find that LAEs with fainter far-UV luminosities have larger EWs. Finally, we derived the far-UV luminosity function of LAEs down to Mₔₕ -19. 6 using the photometric sample, and compared it with that of Lyman-break galaxies (LBGs). We find that as high as about 80% of LBGs at z 6 have W₀^i 100 \, Å, in sharp contrast to lower-z counterparts.