Empirical Estimate of Lyman-alpha Escape Fraction in a Statistical
  Sample of Lyman-alpha Emitters
  The Lyman-alpha (Lya) recombination line is a fundamental tool for galaxy
evolution studies and modern observational cosmology. However, subsequent
interpretations are still prone to a number of uncertainties. Besides numerical
efforts, empirical data are urgently needed for a better understanding of Lya
escape process. We empirically estimate the Lyman-alpha escape fraction
fesc(Lya) in a statistically significant sample of z ~ 0 - 0.3 galaxies in
order to calibrate high-redshift Lyman-alpha observations. An optical
spectroscopic follow-up of a sub-sample of 24 Lyman-alpha emitters (LAEs)
detected by GALEX at z ~ 0.2-0.3, combined with a UV-optical sample of local
starbursts, both with matched apertures, allow us to quantify the dust
extinction through Balmer lines, and to estimate the Lyman-alpha escape
fraction from the Halpha flux corrected for extinction in the framework of the
recombination theory. The global escape fraction of Lyman-alpha radiation spans
nearly the entire range of values, from 0.5 to 100 %, and fesc(Lya) clearly
decreases with increasing nebular dust extinction E(B-V). Several objects show
fesc(Lya) greater than fesc(continuum) which may be an observational evidence
for clumpy ISM geometry or for an aspherical ISM. Selection biases and aperture
size effects may still prevail between z ~ 0.2-0.3 LAEs and local starbursts,
which may explain the difference observed for fesc(Lya).
