R. B. Partridge
Near the center of this field, an isolated, negative feature was found. It was with a peak central amplitude of 250 . We interpret it as the Sunyaev--Zel'dovich signal from a high redshift cluster. Interestingly, within about of this decrement, lie two radio-quiet quasars both at . If the signal is from a cluster of galaxies, failure to observe the source in a deep ROSAT exposure suggests its redshift must exceed 1.5. There is no optical evidence from the MDS survey frames for a cluster in the vicinity of the microwave decrement, again suggesting high redshift.
This detection is very similar to one to be discussed at this conference by the Cambridge group; I suggest we refer to these objects as ``Black Clouds'' to honor Sir Fred Hoyle.