Finding AGN in cluster galaxies

Advisor: For your thesis, we should look at the fraction of AGN in clusters. Why don't you go dig through the data archives and see what you come up with?

Student: uh, OK.

So what do you do? This is an excellent example of a multiwavelength data mining task. We'll combine optical and X-ray data to study AGN in clusters.

Step I: Identify some galaxy clusters. We'll start with the soft X-ray selected ROSAT Brightest Cluster Sample, and I'm providing a easy to read data table. From that, we want to select clusters that we also have optical and hard X-ray data for.

Step II: Get the SDSS optical photometry and spectroscopy of galaxies within 1 Mpc of the cluster center. Build a color-magnitude diagram for the cluster, first for all (non-stellar) objects, and then for spectroscopically confirmed cluster members (what is your criterion for "spectroscopically confirmed"?). Use these plots to identify the red sequence, and thereby assign "photometric cluster membership".

Step III: Search the Chandra source catalog for hard X-ray point sources around the cluster -- these are likely AGN. Cross-match them with your optical galaxy catalog, and plot them on your cluster color-magnitude diagram. What can you say about their cluster membership? What kind of galaxies do they live in? Make sure you look individually at every cross-matched source brighter than r=20.5.

Step IV: Write up your results in the form of a short thesis proposal to your advisor. Here is an example (courtesy Craig Rudick, although this doesn't follow the format below). Your write-up should have the following format:

Intro: why is this an interesting problem? what has been done before?
Techniques: What you did in your data mining task. Describe how you chose your clusters. Show your color-mag plots for each cluster, and explain how you defined the red sequence.
Results: Did you find AGN in clusters? How many? With what certainty? Other than AGN in clusters, what kind of objects did you find? What were the limitations of what you did?
Future steps: What would the next step be? What data would you need to actually get a better handle on the problem?
The writeup should be ~ 5 pages of text, plus figures and references.

The archival data retrieval for steps I, II, and III will be done in class in groups. Any subsequent analysis and discussion should also be done in your group. The writeup (step IV) should be your own writeup.

Notes:

We will be working at distances were cosmological effects will start becoming noticeable. So don't use Hubble's law to get "a distance". Instead, use the cluster redshift to get luminosity distances and angular size distances for calculating spatial sizes and luminosities, respectively. Ned Wright's cosmology calculator will be helpful for this.
SDSS footprint