Maybe lensing, maybe starburst

https://www.legacysurvey.org//viewer/?ra=331.2789&dec=1.7845&layer=hsc-dr2&zoom=15

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And a Tidal-Tail?

Yes. The presence of a tidal tail from possible interaction with the second galaxy is why I proposed that the blue arc might be starburst rather than gravitational lensing. When galaxies collide and stars are thrown out as a tidal trail, the trail often becomes excited into lots of new star formation, so you often see streaks of blue near interacting galaxies. If the galaxies are relatively close you can usually see what is causing it, but with distant galaxies like this it is hard to tell one from the other - it needs a high resolution image taken by Hubble to distinguish them, or spectroscopic analysis of the light in the streak. If it is gravitational lensing, the light in the streak will be more highly red-shifted than the light from the main galaxy, as it comes from a much more distant source.

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