Scientists: please clarify lensing by spirals
After some Googling around, I'm getting the idea that edge-on spirals sometimes create lenses of quasars. I haven't found any references to lensing of any other type of galaxy...so it seems unlikely that a front-on spiral would create arc-type lensing. I see that lots of us are marking those, and the sims are sometimes ambiguous or misleading. Can we get the science clear so we don't waste our own time, or yours? TIA
by psaha scientist
Nice explanation by Tom Collett on another thread.
Also worth looking for two other clues: First, the image colors should match. Lensing itself does not change the colors at all, but differential absorption can modify the colors a little, in which case the image closer to the galaxy may be slightly redder. Second, the positioning of the images will be somehow ``lens-like''. This is hard to describe in words, but check out LensToy to get a feeling for how lensed images tend to arrange themselves.