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Session 106 - Clusters of Galaxies.
Display session, Saturday, January 10
Exhibit Hall,
We have obtained U-band polarimetry of the blue optical continuum that is coincident with the FR I radio source PKS 2322-122 in the Abell 2597 cluster central galaxy. We find a three sigma upper limit to the degree of polarization of the optical continuum of less than 5%. The accuracy of the measurement is limited by diluting galactic starlight. This limit is inconsistent with the blue continuum being primarily scattered light or synchrotron emission, and it excludes models for the blue continuum being scattered light from an active nucleus that is hidden from direct view. Essentially all of the data pertaining to the blue continuum along the radio source, or ``blue lobes'', indicate that they are regions of recent star formation. The spatial coincidence between the blue lobes and disturbances in the radio source suggest that star formation was induced by an interaction between the radio source and the cool (<10^4K), surrounding gas.
