Lyman Alpha Emitters in Hierarchical Galaxy Formation II. UV Continuum
  Luminosity Function and Equivalent Width Distribution
  We present theoretical predictions of UV continuum luminosity function (UV
LF) and Lya equivalent width (EW) distribution of Lyman alpha emitters (LAEs)
in the framework of the hierarchical clustering model of galaxy formation. The
model parameters about LAEs were determined by fitting to the observed Lya LF
at z=5.7 in our previous study, and the fit indicates that extinction of Lya
photons by dust is significantly less effective than that of UV continuum
photons, implying clumpy dust distribution in interstellar medium. We then
compare the predictions about UV LFs and EW distributions with a variety of
observations at z ~ 3-6, allowing no more free parameters and paying careful
attention to the selection conditions of LAEs in each survey. We find that the
predicted UV LFs and EW distributions are in nice agreement with observed data,
and especially, our model naturally reproduces the existence of large EW LAEs
(> 240 A) without introducing Pop III stars or top-heavy initial mass function.
We show that both the stellar population (young age and low metallicity) and
extinction by clumpy dust are the keys to reproduce large EW LAEs. The evidence
of EW enhancement by clumpy dust is further strengthened by the quantitative
agreement between our model and recent observations about a positive
correlation between EW and extinction. The observed trend that brighter LAEs in
UV continuum tend to have smaller mean EW is also reproduced, and the clumpy
dust is playing an important role again for this trend. We suggested in our
previous study that the transmission of intergalactic medium for Lya emission
rapidly decreases from z ~ 6 to 7 by the fitting to Lya LFs, and this evidence
is quantitatively strengthened by the comparison with the UV LF and EW
distribution at z ~ 6.6.
