Here is the 7.91micron image (infrared image) of M66 taken by the Spitzer Telescope with its Irac instrument, showing the nature of the pronounced arm asymmetry in M66:
(this image is displayed at a linear scale)
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Here is the Far-ultraviolet channel from the GALEX image of M66:
(image displayed at a logarithmic scale)
Note the single Really Unusual and Very Large and very luminous Far-ultraviolet emitting Knot or Radial Feature!!
"Curioser and Curioser, said the white rabbit"