Things to think about when looking at cross-matched sources in Navigator

For each cluster, make a final sample of all crossmatched sources that are brighter than r=20.5 and bluer than g-r=1.1. Then use their SDSS coordinates ('ra_SDSS' and 'dec_SDSS' in your data table) to look them up on the SDSS Navigator site (https://skyserver.sdss.org/dr18/VisualTools/navi).

While looking at your sources, think about the following things.

Is it a good X-ray/optical cross-match? Think about different cases:

X-ray source close to an optical source, small X-ray position uncertainty.
X-ray source close to an optical source, but large X-ray uncertainty.
X-ray source far from an optical source.
X-ray source in a crowded optical field.

Is it likely to be in the cluster?

If it has a spectroscopic redshift, you know whether or not it is in the cluster.
What if it doesn't have a spectrum? What other arguments could you make?

What kind of galaxy is it in?

Morphology: Spiral? Elliptical? Interacting?
Where is it in/around the cluster? Inner parts? Outskirts?
Color: Blue cloud? Red sequence?
SDSS Spectroscopic Classification: star forming? non-star-forming? AGN noted in classification?

X-ray hardness ("HRhs" column in the dataset)

Logarithmic measure of ratio of hard:soft X-rays. Larger number, harder spectrum (more energectic X-rays)
HRhs > −0.5: very likely AGN
HRhs < −0.5: uncertain, but possibly an AGN (soft X-rays could also be from a hot gas halo around the galaxy, maybe?)
Also think about the quality of the X-ray hardness measurement, things with low S/N are less certain.