Time for some more pretty pictures of hydrogen....
It's proving surprisingly difficult to convince people that some streams I've found in the Virgo cluster radio data are real. So to settle the matter once and for all, I've resorted to creating synthetic galaxies and adding fake streams and noise extracted from real data. Then I blindly search the data, labelling what I think looks like a stream and what doesn't. Since I don't know in advance which galaxies have streams or not, this should be a good way to quantify very rigorously how many false positives can occur just due to the noise, as well as measuring how many of the known fake streams would actually be detected by the search technique.
Each of these 100 pillars is a synthetic galaxy, with the vertical axis being velocity. Each of the "segments" is a contour at a different velocity channel, extended into 3D. Real galaxies would look a bit more complicated than this, but these are good enough to search for features as extended as the ones in the real data. Arranging them into a neat grid makes it easy to search the whole data set very quickly and isn't just for the sake of making something minimalist.
You can't really see the fake extensions from this angle - they're more visible from underneath. This particular data set has a stream in every galaxy, always pointing in the same direction. For the real search I vary the length, angle, brightness, presence, and number of velocity channels of the streams.
These pretty pictures aren't going in the paper - for that, I'm showing a boring but more easily comprehensible 2D plot. They look nice though.
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