Small‐Scale Cosmic Microwave Background Observations at 8.4 GHz

We have used the Very Large Array (VLA) of the National Radio Astronomy Observatory at 8.44 GHz to image a ~40 arcmin 2 field with an uprecedented rms sensitivity of 1.5 μJy. After correcting for the effects of discrete foreground radio sources, we examined this most sensitive microwave image of the sky for fluctuations in the cosmic microwave background radiation (CBR). At the 6'' resolution of our VLA map, Δ T / T ≈ (0.7 ± 0.8) × 10 -4 , with an upper limit of 1.3 × 10 -4 at 95% confidence. At 1' resolution, we measure a fluctuation amplitude of Δ T / T = (1.2 ± 1.4) × 10 -5 . We also report on our observations of the linear and circular polarization of the CBR for which we derive upper limits (at 95% confidence) of Δ T / T ≤ 1.1 × 10 -5 and Δ T / T ≤ 1.6 × 10 -5 , respectively, on an angular scale of 1'.