Multi-band observations of the galaxy cluster Abell 2319
This series of images shows Abell 2319, a nearby cluster of galaxies, in seven different frequency channels, from 44 to 545 GHz. The characteristic frequency dependence of the Sunyaev-Zel'dovich Effect is evident from a comparison of the various images.
In the four left-most frames, corresponding to frequencies lower than 217 GHz, the signal is negative (represented in blue), meaning that the cluster appears colder than the average CMB signal, whereas in the two right-most ones, corresponding to frequencies higher than 217 GHz, the cluster appears hotter than average, hence exhibiting a positive signal (represented in red). The absence of any signal at the null-point frequency of 217 GHz is a characteristic of the Sunyaev-Zel'dovich Effect.
Thanks to both the High Frequency Instrument (HFI) and the Low Frequency Instrument (LFI), Planck has an unprecedented coverage across the microwave region of the electromagnetic spectrum, which makes it an ideal tool to hunt for the Sunyaev-Zel'dovich Effect arising from clusters and super-clusters of galaxies, the largest structures in the Universe.
The size of each frame is about 2 degrees.