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