A search for Ly alpha emitters at redshift 3.7

We present the results of a survey for emission-line objects, based on optical intermediate-band (lambda(c) = 5736 Angstrom and Deltalambda = 280 Angstrom) and broadband (B, V, R, and i') observations of the Subaru/XMM-Newton Deep Field with the 8.2 m Subaru telescope and the Subaru Prime Focus Camera (Suprime-Cam). All the data were obtained during the guaranteed time observations of the Suprime-Cam instrument. The intermediate-band image covered a sky area of 10.'62 x 12.'40 approximate to132 arcmin(2) in the Subaru/XMM-Newton Deep Field (Ouchi et al.). Using this image, we found 23 emission-line sources whose observed emission-line equivalent widths are greater than 250 Angstrom. Their optical multicolor properties indicate that six emission-line sources are Lyalpha emitters at z approximate to 3.7 (Deltaz approximate to 0.22). They are either intense starburst galaxies or active galactic nuclei like quasars at z approximate to 3.7. Two more emission-line sources may also be Lyalpha emitters at z approximate to 3.7, although their multicolor properties are marginal. Among the remaining 15 emission-line objects, eight objects appear to be strong emission-line galaxies at lower redshift; e. g., [OII] lambda3727 emitters at z approximate to 0.54, Hbeta at z approximate to 0.18, or [O III] lambda5007 emitters at z approximate to 0.15. The remaining seven objects are unclassified because they are too faint to be detected in broadband images. We discuss the observational properties of these strong emission-line sources. In particular, our data allow us to estimate the star formation density at z approximate to 3.7 for the first time.