The source of leaking ionizing photons from Haro11 -- Clues from HST/COS
  spectroscopy of knots A, B and C
  Understanding the escape of ionizing (Lyman continuum) photons from galaxies
is vital for determining how galaxies contributed to reionization in the early
universe. While directly detecting Lyman continuum from high redshift galaxies
is impossible due to the intergalactic medium, low redshift galaxies in
principle offer this possibility, but requirie observations from space. The
first local galaxy for which Lyman continuum escape was found is Haro11 , a
luminous blue compact galaxy at z=0.02, where observations with the FUSE
satellite revealed an escape fraction of 3.3 %. However the FUSE aperture
covers the entire galaxy, and it is not clear from where the Lyman continuum is
leaking out. Here we utilize HST/COS spectroscopy in the wavelength range
1100-1700 A of the three knots (A, B, and C) of Haro11 to study the presence of
Ly-$\alpha$ emission and the properties of intervening gas. We find that all
knots have bright Ly-$\alpha$ emission. UV absorption lines, originating in the
neutral interstellar medium, as well as lines probing the ionized medium, are
seen extending to blue shifted velocities of 500 km/s in all three knots,
demonstrating the presence of an outflowing multiphase medium. We find that
knots A and B have large covering fractions of neutral gas, making LyC escape
along these sightlines improbable, while knot C has a much lower covering
fraction ($\lesssim50$%). Knot C also has the the highest Ly-$\alpha$ escape
fraction and we conclude that it is the most likely source of the escaping
Lyman continuum detected in Haro11.
