A search for Population III galaxies in CLASH. I. Singly-imaged candidates at high redshift

TL;DR

This study searches for Population III galaxy candidates at high redshift in CLASH data, identifying five potential objects with Lya-like colors, but only two are strongly consistent with Population III models upon detailed analysis.

Contribution

The paper introduces a new method to identify Population III galaxy candidates using broadband photometry and lensing data, and reports five new candidates with detailed spectral modeling.

Findings

Identified five high-redshift galaxy candidates with Lya-like colors.

Only two candidates are well-fitted by Population III models.

None of the candidates have been previously reported.

Abstract

Population III galaxies are predicted to exist at high redshifts and may be rendered sufficiently bright for detection with current telescopes when gravitationally lensed by a foreground galaxy cluster. Population III galaxies that exhibit strong Lya emission should furthermore be identifiable from broadband photometry because of their unusual colors. Here, we report on a search for such objects at z > 6 in the imaging data from the Cluster Lensing And Supernova survey with Hubble (CLASH), covering 25 galaxy clusters in 16 filters. Our selection algorithm returns five singly-imaged candidates with Lya-like color signatures, for which ground-based spectroscopy with current 8-10 m class telescopes should be able to test the predicted strength of the Lya line. None of these five objects have been included in previous CLASH compilations of high-redshift galaxy candidates. However, when large grids of spectral synthesis models are applied to the study of these objects, we find that only two of these candidates are significantly better fitted by Population III models than by more mundane, low-metallicity stellar populations.