June 1 2022
Single-frame 5 sigma point source depth for ATLAS is around 19.5, sky-limited. A stack of 100 images has 10X SNR so 5 sigma depth is 10X fainter, or 2.5 mag which gets us to 22nd.
Two-band images give us a magnitude and a single color. Balmer break is at 364.5 nm. ATLAS band edges are:
blue edge of c: 420 nm, transition at z of 0.15
red edge of c and blue edge of c: 550 nm, transition at z of 0.51
red edge of c: 650 nm, transition at z of 0.81.
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.
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