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Session 110 - Imaging of Cluster Galaxies.
Display session, Thursday, January 18
North Banquet Hall, Convention Center
We have obtained U-band polarimetry of the blue optical lobes located along the radio lobes of the FR I radio source in the Abell 1795 cluster central galaxy (z=0.063) [McNamara amp; O'Connell 1993, AJ, 105, 417]. We find an upper limit to the degree of polarization of the light emitted from the lobes to be <7%. The accuracy of this measurement is limited by the presence of diluting background starlight.
This limit is inconsistent with scattered light that originated in an obscured, anisotropically radiating nucleus, unless the radiation is beamed by <20\deg to the line of sight, which is unlikely. The absence of a detailed correspondence between the radio lobes and optical lobes and the absence of a polarized signal is likewise inconsistent with synchrotron light.
The blue optical lobes are probably regions of vigorous star formation. If a burst of star formation was triggered by the expanding radio lobes, the age of the burst population should be comparable to the radio age of \sim 10^7 yr. Then, the star formation rate in both lobes, assuming the Local IMF, is \sim 20 M_ødot yr^-1 and the stellar mass of the lobes is \sim 10^8 M_ødot. The material fueling the star formation and the radio source may have originated from the cooling flow or accretion from one or more gaseous cluster galaxies.
