1°- and 2°.5-scale interferometric surveys in the northern sky at 5 GHz

Abstract

We present observations from a 5-GHz short-baseline interferometer at Jodrell Bank, which has been operating at spacings of 0.702 and 1.79m between 1990 and 1997. These surveys covered 2 sr of the sky between Dec. = +30° and +55°, at rms sensitivities of 10 and 8 μK, on angular scales of ≃1° (ℓ = 184 ± 15) and ∼2°.5 (ℓ = 71 ± 13) respectively. This sensitivity was achieved by using the maximum entropy method (MEM) to find the most probable underlying sky fluctuations. We have used the Green Bank 5-GHz catalogue to model point source contributions, tor subtraction from the survey at each spacing. The resulting rms signal measured at intermediate and high Galactic latitudes, in directions away from strong extragalactic sources is 50 ± 6 μK at the shorter spacing and 54 ± 3 μK at the longer spacing. Allowing for the interferometer window function and a contribution arising from uncorrected point source variability, these values correspond to intrinsic rms levels of 373 ± 55 and 1080 ± 120 μK for narrow and wide spacings. We compare these values with measurements at 10 GHz and conclude that between these frequencies the Galactic spectrum is predominantly synchrotron in nature. Further comparison with the Tenerife experiments, sensitive to different angular scales, suggests that the angular power spectrum is flat (ℓ-2) over the observed ℓ-range.