Detection of a Small Scale Cosmic Background Anisotropy at 3.6 cm

We report on the detection of a feature with negative radio flux in a sensitive, low resolution observation with the VLA. This morphologically peculiar feature is approximately 25" 65" in size with a peak central amplitude of about -0.25 mK compared to the brightness temperature of the background sky at 3.6 cm. Within about 1' of this microwave decrement, we also found two radio quiet quasars, both at 2.561, with a projected physical separation of about 1 Mpc ($q_o$ = 0.5, h = 0.5), suggestive of a possible galaxy cluster in the region. We are unable to account for this negative source by systematic phase fluctuations within our observations, sidelobe artifacts, or instrumental noise. We discuss possible physical origins of this microwave source, in particular the inverse-Compton scattering of the cosmic microwave background by hot gas in a distant cluster of galaxies.

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