We are using LSST DM v18 to process the data of galaxy clusters from DECam. We are mainly using the default settings of DM, and for background subtraction we just use the default setting.
We find in the output of
deepCoadd/band_name/tract_number/patch_number.fits), the outer envelopes of bright giant galaxies and bright stars are over-subtracted. Here are some examples.
Example1: on the left is a coadded patch near the center of a cluster (r band), and on the right is a temporary exposure generated by
makeCoaddTempExp (at the same patch).
Example2: a coadded image and a temporary exposure of another cluster. The cluster’s center galaxy (BCG) is at top right, one elliptical galaxy is the center, and a bright star is at bottom left. The black lines near the BCG comes from the edge of a CCD (the bleed trail from a bright star touched the edge of the CCD and caused this on the raw image).
How should we adjust the config files (of processCcd and coaddition) to avoid these?
PS: We also notice sometimes there are some diffuse faint vertical light perpendicular to the bleed trail: please see the two bright stars at top left (this is g band and we notice it in u band). Can it be cleaned by background subtraction?
Sometime we could see on
calexp the background of one CCD chip was divided into 4 parts (top left, top right, bottom left, bottom right) but the difference is small. Do we need to adjust some settings in the config file to correct it? (Perhaps coaddition could automatically fix this?)