Escape of Lyman-alpha and continuum photons from star-forming galaxies
  A large number of high-redshift galaxies have been discovered via their
narrow-band Lya line or broad-band continuum colors in recent years. The nature
of the escaping process of photons from these early galaxies is crucial to
understanding galaxy evolution and the cosmic reionization. Here, we
investigate the escape of Lya, non-ionizing UV-continuum (l = 1300 - 1600
angstrom in rest frame), and ionizing photons (l < 912 angstrom) from galaxies
by combining a cosmological hydrodynamic simulation with three-dimensional
multi-wavelength radiative transfer calculations. The galaxies are simulated in
a box of 5^3 h^-3 Mpc^3 with high resolutions using the Aquila initial
condition which reproduces a Milky Way-like galaxy at redshift z=0. We find
that the escape fraction (fesc) of these different photons shows a complex
dependence on redshift and galaxy properties: fesc(Lya) and fesc(UV) appear to
evolve with redshift, and they show similar, weak correlations with galaxy
properties such as mass, star formation, metallicity, and dust content, while
fesc(Ion) remains roughly constant at ~ 0.2 from z ~ 0 - 10, and it does not
show clear dependence on galaxy properties. fesc(Lya) correlates more strongly
with fesc(UV) than with fesc(Ion). In addition, we find a relation between the
emergent Lya luminosity and the ionizing photon emissivity of Lyman Alpha
Emitters (LAEs). By combining this relation with the observed luminosity
functions of LAEs at different redshift, we estimate the contribution from LAEs
to the reionization of intergalactic medium (IGM). Our result suggests that
ionizing photons from LAEs alone are not sufficient to ionize IGM at z > 6, but
they can maintain the ionization of IGM at z ~ 0 - 5.
