2005MNRAS.360L..10C

Polarized diffuse emission observations at 2.3 GHz in a high Galactic latitude area are presented. The 2°x 2° field, centred at (α= 5^h, δ=-49°), is located in the region observed by the BOOMERanG experiment. Our observations were carried out with the Parkes radio telescope, and represent the highest frequency detection to date in a low-emission area. Because of the weaker Faraday rotation effect, the high frequency allows an estimate of the Galactic synchrotron contamination of the cosmic microwave background polarization (CMBP) which is more reliable than that achieved at 1.4 GHz. We find that the angular power spectra of the E- and B-modes have slopes of β_E=-1.46±0.14 and β_B=-1.87±0.22, indicating a flattening with respect to 1.4 GHz. Extrapolated up to 32 GHz, the E-mode spectrum is about three orders of magnitude lower than that of the CMBP, allowing a clean detection even at this frequency. The best improvement concerns the B-mode, for which our single-dish observations provide the first estimate of the contamination on angular scales close to the CMBP peak (about 2°). We find that the CMBP B-mode should be stronger than the synchrotron contamination at 90 GHz for models with tensor-to-scalar perturbation ratio T/S > 0.01. This low level could move down to 60-70 GHz the optimal window for CMBP measurements.