Polarization Observations in a Low Synchrotron Emission Field at 1.4 GHz

We present the first observation of the diffuse polarized synchrotronradiation of a patch ($\sim 3^\circ \times 3^\circ$) in the BOOMERanG field,one of the areas with the lowest CMB foreground emission. The work has beencarried out with the Australia Telescope Compact Array at 1.4 GHz with 3.4arcmin resolution and sensitivity of $\sim 0.18$ mJy beam$^{-1}$. The meanpolarized signal has been found to be $P_{rms} = \sqrt{(Q_{rms}^2 + U_{rms}^2)}= 11.6 \pm 0.6$ mK, nearly one order of magnitude below than in the GalacticPlane. Extrapolations to frequencies of interest for cosmological investigationssuggest that polarized synchrotron foreground noise should allow the detectionof the CMB Polarization $E$--mode already at 32 GHz and make us confident that,at 90 GHz, it is accessible with no relevant foreground contamination. Last butnot least, even the $B$--mode detection for $T/S > 0.01$ is not ruled out insuch a low emission patch.Comment: Uses emulateapj.sty, onecolfloat.sty, 5 pages 4 fig., accepted for publication in ApJ