Things to think about when looking at cross-matched sources in
Is it a good X-ray/optical cross-match? Think about different
- X-ray source close to an optical source, small X-ray position
- X-ray source close to an optical source, but large X-ray
- 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
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 (soft X-rays: hot gas halo around
the galaxy, maybe?)