Polarization Observations of NGC 315 with FAST

We present new continuum and polarization observations of radio galaxy NGC 315 obtained with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) over 1.0-1.5 GHz. The FAST data detect diffuse large-scale polarized emission with a noise level of 0.065 mJy beam$^{-1}$ at resolution of $4'$. We derived a rotation measure (RM) map with an error of 1.1 rad m$^{-2}$ including systematic error. The intrinsic RM map was obtained after subtracting the Galactic foreground contribution. We estimated a total magnetic field strength of $\lesssim 1$ $μ$G across the source and a thermal electron density of $\sim 10^{-4}$ cm$^{-3}$ toward the northwest lobe. The fractional polarization analysis suggests a random magnetic-field component over a large area toward the northwest lobe.