Deep 1.4‐GHz observations of diffuse polarized emission

ABSTRACT Polarized diffuse emission observations at 1.4 GHz in a high Galactic latitude area of the Northern celestial hemisphere are presented. The 3.2 × 3.2 deg 2 field, centred at RA = 10 h 58 m , Dec. =+42°18′ (B1950) , has Galactic coordinates l ∼ 172°, b ∼+63° and is located in the region selected as northern target of the Balloon‐borne Radiometers for Sky Polarization Observations experiment. Observations have been performed with the Effelsberg 100‐m telescope. We find that the angular power spectra of the E and B modes have slopes of β E =−1.79 ± 0.13 and β B =−1.74 ± 0.12 , respectively. Because of the very high Galactic latitude and the smooth emission, a weak Faraday rotation action is expected, which allows both a fair extrapolation to cosmic microwave background polarization (CMBP) frequencies and an estimate of the contamination by the Galactic synchrotron emission. We extrapolate the E ‐mode spectrum up to 32 GHz and confirm the possibility to safely detect the CMBP E ‐mode signal in the Ka band found in another low‐emission region. Extrapolated up to 90 GHz, the Galactic synchrotron B mode looks to compete with the cosmic signal only for models with a tensor‐to‐scalar perturbation power ratio T / S < 0.001 , which is even lower than the T / S value of 0.01 found to be accessible in the only other high Galactic latitude area investigated to date. This suggests that values as low as T / S = 0.01 might be accessed at high Galactic latitudes. Such low‐emission values can allow a significant redshift of the best frequency to detect the CMBP B mode, also reducing the contamination by Galactic dust, and opening interesting perspectives to investigate inflation models.