https://www.legacysurvey.org//viewer/?ra=115.2668&dec=54.4302&layer=ls-dr10-grz&zoom=13&ngc
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Why this occurs, from what I learned with dstn a while back
The northern MzLS + BASS survey uses two different telescopes. The z-band uses the Mayall telescope, and the g-band and r-bands use the Bok telescope. Sadly, the Bok does not include the z-band. Also, the Mosaic camera on the Mayall telescope has been retired and disassembled.
The known issue is that MzLS is much deeper than the SDSS z band – it’s an issue related to estimating the background around bright galaxies.
I believe the problem is related to a step in the Mosaic adaptation of the Community Pipeline (which processes raw exposures into calibrated & corrected exposures, and is the input to the Legacypipe processing). That Mosaic3 camera had a “pattern noise” issue, basically a periodic electronic signal that added patterned noise to the images. The CP attempts to estimate and remove that pattern noise. However – and here I don’t really know or understand the details – the algorithm it uses for this results in subtracting real signal on large galaxies. This results in removing z-band (red, in these images) light from the centers of larger galaxies.
cheers,
dustin
Thanks, did not know about adaptions to the community pipeline about MzLS survey images. Read about the pattern noise issue.