We observed the inner filament of NGC 5128 (Centaurus A) with the Hubble Space Telescope Wide Field Camera 3 (WFC3), using the F225W, F657N and F814W filters. We find a young stellar population near the south-west tip of the filament. We constrain the ages of these stars to 1-3 Myrs. No further recent star formation is found along the filament.

We propose an updated explanation for the origin of the inner filament. It has been suggested Sutherland et al.1993 that radio jets can shock the surrounding gas, giving rise to 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. We suggest such a shock has overrun a molecular cloud, triggering star formation in the dense molecular core. The outer, more diffuse parts of the cloud are then ablated and shock heated, giving rise to the observed optical line and X-ray emission.