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Session 104 - Radio Galaxies, Radio Observations of AGN Jets & Outflows.
Display session, Saturday, January 10
Exhibit Hall,
Observational evidence for shock-induced star formation is found in the NE radio lobe of the nearby radio galaxy Centaurus A (NGC 5128). A gas cloud, recently mapped in H I, is impacted by the adjacent radio jet to the extent that cloud collapse is triggered and loose chains of blue supergiant stars are formed. Diffuse clouds and filaments of ionized gas have been detected near the interface of the H I cloud and the radio jet. New observations of this gas have been made at Las Campanas Observatory. These show velocities which cover a range more than 550 km s^-1 . Line intensities in the spectra are characteristic of a shock-related origin with strong [N II] and [S II] relative to H\alpha. The [O III]/H\alpha line ratio indicates a large range in excitation which is not correlated with velocity. The star-forming process appears similar to that proposed in our own galaxy involving supernova-induced cloud collapse but with one important difference. The source of the impinging shock is still active and star formation will continue for as long as the gas cloud remains close to the radio jet. The loose chains of blue stars in the area are resolved only because NGC 5128 is so close. The reported faint blue extensions and plumes in more distant analogs probably have a similar origin.
