Triggered star-formation in the inner filament of Centaurus A
  We present recent Hubble Space Telescope observations of the inner filament
of Centaurus A, using the new Wide Field Camera 3 (WFC3) $F225W, F657N$ and
$F814W$ filters. We find a young stellar population near the south-west tip of
the filament. Combining the WFC3 dataset with archival Advanced Camera for
Surveys (ACS) $F606W$ observations, we are able to constrain the ages of these
stars to <=10 Myrs, with best-fit ages of 1-4 Myrs. No further recent
star-formation is found along the filament.
  Based on the location and age of this stellar population, and the fact that
there is no radio lobe or jet activity near the star-formation, we propose an
updated explanation for the origin of the inner filament. Sutherland et al.
(1993) suggested that radio jet-induced shocks can drive the observed optical
line emission. We argue that such shocks can naturally arise due to a weak
cocoon-driven bow shock (rather than from the radio jet directly), propagating
through the diffuse interstellar medium from a location near the inner northern
radio lobe. The shock can overrun a molecular cloud, triggering star-formation
in the dense molecular cores. Ablation and shock heating of the diffuse gas
then gives rise to the observed optical line and X-ray emission. Deeper X-ray
observations should show more diffuse emission along the filament.
