...
LRG's have absolute magnitudes of -22 to -23 (Tal et al MASS GROWTH AND MERGERS: DIRECT OBSERVATIONS OF THE LUMINOSITY FUNCTION OF LRG SATELLITE GALAXIES OUT TO z = 0.7 FROM SDSS AND BOSS IMAGES)
| z | mu |
|---|---|
| 0.2 | 39.7 |
| 0.4 | 41.4 |
| 0.5 | 42 |
| 0.75 | 43.1 |
We can see m=M+mu=22=22 so threshold mu should be 44, corresponding to z of around 0.8. Wow. That's a detection threshold. For getting a decent color we need better than 10% photometry in each band so let's go out to 0.5 for now.
| Object | RA (J2000) | DEC (J2000) | z | notes |
|---|---|---|---|---|
| Abell 2218 | 16:35:52.4 | +66:12:52 | 0.176 | |
| Abell 370 | 02:39:50 | -01:35:08 | 0.375 | |
PSZSPT J0117-5053 | 019.29320144653 | -50.88529205322 | unknown | Planck + SPT cluster but no SPT counterpart so likely low-z |
PSZSPT J0109-4552 | 017.36057472229 | -45.87871932983 | 0.02  | really low-z, likely hard to pick out cluster members? |
Typical cluster sizes are a few arcmin so a stacked image that is 1 deg x 1 deg would be plenty to get comparison regions as well.
tasks:
1) find ATLAS magnitudes of isolated SDSS LRG galaxies and construct photo-z estimator (like redmapper) for these objects.
2) Make star-galaxy discriminator perhaps by including WISE data?
3) extract photometry from stacked images and morphology from stacked images, perhaps add WISE or GAIA data to get another color?
4) make color-magnitude diagram of plausible cluster members and look for LRG finger.
5) run on entire e-Rosita Xray cluster catalog, for example https://www.aanda.org/articles/aa/full_html/2022/05/aa41120-21/aa41120-21.html