  We report the first results from a deep Lya imaging program of local
starburst galaxies with the Advanced Camera for Surveys (ACS) of the Hubble
Space Telescope. The two observed galaxies ESO 350-IG038 and SBS 0335-052 have
luminosities similar to those of the Magellanic Clouds but differ in their
chemical composition. ESO 350-IG038 has an oxygen abundance of 1/8 solar,
whereas SBS 0335-052 is known to have one of the lowest abundances among blue
galaxies (~1/30). The ACS imaging reveals a complex Lya morphology, with
sometimes strong offsets between the emission of Lya and the location of
stellar light, ionized gas traced by Halpha, and the neutral gas. Overall, more
Lya photons escape from the more metal- and dust-rich galaxy ESO 350-IG038. The
absence of clear SBS 0335-052 Lya emission over all observed knots, whatever
their dust content or/and color indices, contradicts model expectations of a
lower escape fraction from dust-rich gas due to destruction of Lya photons by
dust grains. Rather, the results are in qualitative agreement with models
suggesting the kinematic properties of the gas as the dominant Lya escape
regulator. If the properties of the two observed galaxies are representative
for starburst galaxies in general, Lya will be difficult to interpret as a
star-formation indicator, in particular if based on Lya imaging at low spatial
resolution.
