 Solution

The wavelength corresponds to about $15\mathrm{GHz}$, in the low-frequency decrement part of the thermal Sunyaev-Zeldovich effect. Hot cluster electrons inverse-Compton scatter CMB photons. In the Rayleigh-Jeans limit,The signal probes integrated electron pressure. Short baselines give sensitivity to extended arcminute-scale cluster structure, while the primary field covers the cluster and surrounding sky. The array's several-arcminute resolution suits many such structures; it is not equally well matched to every cluster size.

Simultaneous cross-correlations reject uncorrelated receiver noise and provide spatial information; compact radio sources can be constrained with the relatively longer baselines and separated from extended structure. Broad frequency coverage helps sensitivity provided channel smearing is controlled. Correlated atmospheric emission, calibration error, primordial CMB fluctuations and radio-source contamination remain relevant. The lack of zero and very short spacings also means that total integrated cluster flux requires a model or complementary data. An interferometer is therefore useful for the spatially resolved decrement, rather than automatically measuring every cluster's full pressure integral.