Lyman-alpha line profiles are a powerful probe of ISM structure, outflow
speed, and Lyman continuum escape fraction. In this paper, we present the
Lyα line profiles of the COS Legacy Archive Spectroscopic SurveY, a
sample rich in spectroscopic analogs of reionization-era galaxies. A large
fraction of the spectra show a complex profile, consisting of a double-peaked
Lyα emission profile in the bottom of a damped, Lyα absorption
trough. Such profiles reveal an inhomogeneous interstellar medium (ISM). We
successfully fit the damped Lyα absorption (DLA) and the Lyα
emission profiles separately, but with complementary covering factors, a
surprising result because this approach requires no Lyα exchange between
high-NHI and low-NHI paths. The combined distribution
of column densities is qualitatively similar to the bimodal distributions
observed in numerical simulations. We find an inverse relation between
Lyα peak separation and the [O III]/[O II] flux ratio, confirming that
the covering fraction of Lyman-continuum-thin sightlines increases as the
Lyα peak separation decreases. We combine measurements of Lyα
peak separation and Lyα red peak asymmetry in a diagnostic diagram which
identifies six Lyman continuum leakers in the CLASSY sample. We find a strong
correlation between the Lyα trough velocity and the outflow velocity
measured from interstellar absorption lines. We argue that greater vignetting
of the blueshifted Lyα peak, relative to the redshifted peak, is the
source of the well-known discrepancy between shell-model parameters and
directly measured outflow properties. The CLASSY sample illustrates how
scattering of Lyα photons outside the spectroscopic aperture reshapes
Lyα profiles as the distances to these compact starbursts span a large
range.Comment: 40 pages, 19 figures, 5 tables, submitted to ApJ, comments welcom