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

Abstract

Observations with Subaru telescope have detected surprisingly strong Lyman continuum (LyC; $\sim 900$ Å 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 $Z\ge 1/50Z_{\odot }$ can explain the observed LyC strength only with a very top-heavy initial mass function (IMF; $<m>\sim 50M_{\odot }$). However, the critical metallicity for such an IMF is expected to be much lower. A very young ($\sim 1$ Myr) and massive ($\sim 100$ $M_{\odot }$) extremely metal-poor ($Z\le 5\times 10^{-4}{Z}_{\odot }$) 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 $\sim 1$% in total stellar mass of the LAEs.

arXiv comment4 pages, 2 figures, First Stars IV in Kyoto conference (May 2012) proceeding