Coadded 5^∘ × 5^∘ W2-band image (between 2009 and 2022) of the region surrounding Cas A taken from unwise, overlaid with a map of the echo positions (red dots) and all other sources (blue dots) identified in our search. The black square inset shows a zoom-in of the region with a particularly high spatial density complex of echo features. The position of Cas A is indicated by the yellow crosshair, and the image spatial scale and orientation are indicated.

(The data used to create this figure are available in the online article.)

(The data used to create this figure are available.)