U-Band Polarimetry of the Radio-aligned Optical Continuum in the Abell 1795 Cluster Central Galaxy

Abstract

We have obtained U-band polarimetry of the lobes of blue optical continuum located along the z = 0.063 F-R I radio source in the Abell 1795 cluster central galaxy. We find an upper limit to the degree of polarization of the light emitted from the lobes of less than 7%. The accuracy of this measurement is limited by the presence of diluting background starlight. This limit is inconsistent with the lobes being scattered light that originated in an obscured, anisotropically radiating nucleus, Unless the radiation is beamed and is viewed at an angle <~ 22^deg^ to the line of sight, which is unlikely. The absence of a polarized signal and detailed correspondence between the radio lobes and optical lobes is inconsistent with synchrotron light. The blue optical lobes are probably regions of recent star formation. If a burst of star formation were triggered by the expanding radio lobes, the age of the burst population should be ~10^7^ yr. Then, the star formation rate in both lobes, assuming the local IMF, is ~20 M_sun_ yr^-1^, and the stellar mass of the lobes is ~10^8^ M_sun_. 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.