A photometric survey for Lyalpha-HeII dual emitters: Searching for Population III stars in high-redshift galaxies

TL;DR

This study conducted a deep photometric survey in the Subaru Deep Field to identify high-redshift galaxies hosting Population III stars by detecting dual Ly_alpha and HeII emitters, but found no convincing candidates, setting upper limits on PopIII star formation.

Contribution

Introduced a new photometric method combining intermediate, broad, and narrow-band data to search for PopIII-hosting galaxies via dual emission lines at high redshift.

Findings

No convincing Ly_alpha-HeII dual emitters were detected.

The upper limit on PopIII star formation rate density was established.

Most dual emitters identified were lower-redshift contaminants.

Abstract

We present a new photometric search for high-z galaxies hosting Population III (PopIII) stars based on deep intermediate-band imaging observations obtained in the Subaru Deep Field (SDF), by using Suprime-Cam on the Subaru Telescope. By combining our new data with the existing broad-band and narrow-band data, we searched for galaxies which emit strongly both in Ly_alpha and in HeII 1640 (``dual emitters'') that are promising candidates for PopIII-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 [OII]-[OIII] dual emitters or H_beta-(H_alpha+[NII]) dual emitters at z<1, as inferred from their broad-band colors and from the ratio of the equivalent widths. No convincing candidate of Ly_alpha-HeII dual emitter of SFR_PopIII > 2 Msun/yr was found by our photometric search in 4.03 x 10^5 Mpc^3 in the SDF. This result disfavors low feedback models for PopIII star clusters, and implies an upper-limit of the PopIII SFR density of SFRD_PopIII < 5 x 10^-6 Msun/yr/Mpc^3. This new selection method to search for PopIII-hosting galaxies should be useful in future narrow-band surveys to achieve the first observational detection of PopIII-hosting galaxies at high redshifts.