A possible signature of primordial stellar populations in $z=3$ Lyman $\alpha$ emitters

TL;DR

This study suggests that the observed strong Lyman continuum emission from some $z=3.1$ Lyman alpha emitters may originate from either extremely metal-poor Population III stars or a top-heavy initial mass function in more metal-rich populations.

Contribution

It proposes a new interpretation of LyC emission in LAEs, indicating possible signatures of primordial stellar populations or unique IMF conditions.

Findings

Primordial or extremely metal-poor stellar populations can explain LyC strength.

Metallicity of $Z extgreater{}1/50 Z_igodot$ requires a top-heavy IMF.

A small fraction (~1%) of Population III stars can account for observed LyC.

Abstract

Observations with Subaru telescope have detected surprisingly strong Lyman continuum (LyC; $\sim900$ \AA\ in the rest-frame) from some Lyman $\alpha$ emitters (LAEs) at $z=3.1$. We have examined the stellar population which simultaneously accounts for the strength of the LyC and the spectral slope of non-ionizing ultraviolet of the LAEs. As a result, we have found that stellar populations with metallicity $Z\geq1/50 Z_\odot$ can explain the observed LyC strength only with a very top-heavy initial mass function (IMF; $< m > \sim 50 M_\odot$). However, the critical metallicity for such an IMF is expected to be much lower. A very young ($\sim1$ Myr) and massive ($\sim100$ $M_\odot$) extremely metal-poor ($Z\leq5\times10^{-4}Z_\odot$) or metal-free (so-called Population III) stellar population can also reproduce the observed LyC strength if the mass fraction of such 'primordial' stellar population is $\sim1$% in total stellar mass of the LAEs.