A Photometric Survey for Lyα–HeiiDual Emitters: Searching for Population III Stars in High‐Redshift Galaxies

Abstract

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 Lyα and He II λ1640 (dual emitters) and are promising candidates for Pop III-hosting galaxies at 3.93 z 4.01 and 4.57 z 4.65. Although we found 10 dual emitters, most of them turn out to be [O II]-[O III] dual emitters or Hβ-(Hα+[N II]) dual emitters at z < 1, as inferred from their broadband colors and from the ratio of the equivalent widths. No convincing candidate Lyα-He II dual emitter of SFRPopIII 2 M☉ yr−1 was found by our photometric search in 4.03 × 105 Mpc3 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 SFRDPopIII < 5 × 10−6 M☉ 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.