Filamentary Infall of Cold Gas and Escape of Lyman Alpha and Hydrogen
  Ionizing Radiation from an Interacting High-Redshift Galaxy
  We present observations of a peculiar Lyman alpha-emitting galaxy at redshift
3.344, discovered in a deep, blind spectroscopic survey for faint Lyman alpha
emitters with the Magellan II telescope in the Hubble Ultra Deep Field (HUDF).
The galaxy exhibits complex Lyman alpha emission, including an extended,
asymmetric component that is partially suppressed by damped Lyman alpha
absorption, and two spatially elongated, narrow emission features. Archival HST
ACS imaging shows evidence for tidal disruption of the stellar component. This
V=27 galaxy appears to give us unprecedented insights into two fundamental
stages in the formation of structure at high redshift: the inflow of gas into
ordinary galaxies, and the escape of ionizing radiation into the intergalactic
medium. Neutral hydrogen, falling in partly in form of a narrow filament,
appears to emit fluorescent Lyman alpha photons induced by the stellar ionizing
flux escaping from the disturbed galaxy. The in-falling material may represent
primary cold accretion or an interaction-triggered inflow. The rate of ionizing
photons required by the observed Lyman alpha emission is consistent with the
rate of photons produced by the observed stellar population, with roughly 50
percent of ionizing photons escaping from the immediate galaxy and encountering
the in-falling gas. The observational properties of the galaxy lend support to
a picture where galaxy interactions facilitate the escape of both Lyman alpha
and ionizing radiation. We argue that galaxies like the present object may be
common at high redshift. This galaxy may therefore be a late example of an
interacting population of dwarf galaxies contributing significantly to the
reionization of the universe.
