A photometric survey for Lyα-He II dual emitters:: Searching for population III stars in high-redshift galaxies

We present a new photometric search for high-z galaxies hosting Population III (Pop III) stars based on deep intermediate-band imaging observations obtained in the Subaru Deep Field (SDF), using Suprime-Cam on the Subaru Telescope. By combining our new data with the existing broadband and narrowband data, we searched for galaxies that emit strongly in both Ly alpha and He II lambda 1640 (dual emitters) and are promising candidates for Pop III-hosting galaxies at 3: 93 less than or similar to z less than or similar to 4.01 and 4: 57 less than or similar to z less than or similar to 4.65. Although we found 10 dual emitters, most of them turn out to be [O II]-[O III] dual emitters or H beta-(H alpha+[ NII]) dual emitters at z < 1, as inferred from their broadband colors and from the ratio of the equivalent widths. No convincing candidate Ly alpha-He II dual emitter of SFR(PopIII) greater than or similar to 2 M(circle dot) yr(-1) was found by our photometric search in 4.03 x 10(5) Mpc(3) in the SDF. This result disfavors low-feedback models for Pop III star clusters and implies an upper limit on the Pop III SFR density of SFRD(PopIII) < 5 x 10(-6) M(circle dot) yr(-1) Mpc(-3). This new selection method to search for Pop III-hosting galaxies should be useful in future narrowband surveys to achieve the first observational detection of Pop III-hosting galaxies at high redshifts.