Ly{\alpha} Emission from High Redshift Sources in COSMOS
  We investigate spectroscopically measured Ly{\alpha} equivalent widths and
escape fractions of 244 sources of which 95 are Lyman Break Galaxies (LBGs) and
106 Lyman Alpha Emitters (LAEs) at z~4.2, z~4.8, and z~5.6 selected from
intermediate and narrow band observations. The sources were selected from the
Cosmic Evolution Survey (COSMOS), and observed with the DEIMOS spectrograph. We
find that the distribution of equivalent widths shows no evolution with
redshift for both the LBG selected sources and the intermediate/narrowband
LAEs. We also find that the Ly{\alpha} escape fraction of intermediate and
narrow band LAEs is on average higher and has a larger variation than the
escape fraction of LBG selected sources. The escape fraction does not show a
dependence with redshift. Similar to what has been found for LAEs at low
redshifts, the sources with the highest extinctions show the lowest escape
fractions. The range of escape fractions increases with decreasing extinction.
This is evidence that the dust extinction is the most important factor
affecting the escape of Ly{\alpha} photons, but at low extinctions other
factors such as HI covering fraction and gas kinematics can be just as
effective at inhibiting the escape of Ly{\alpha} photons.
