FAQ

Silly

What's in your logo?

"ROSAT PSPC image of the Sun" (by Maxim Markevitch).

Why is it your logo?

Our survey is based on X-ray observations with the ROSAT PSPC (in fact, the yellow-magenta circle approximately corresponds to the central region of the PSPC field of view where we looked for clusters). Also, because many in our team work for SAO.

Sample selection

Most clusters have cooling flows. Don't you miss them because they look like point sources?

In fact, there is little or no difference in the detectability of high-redshift clusters with flat cores and with cooling flows. We have explicitly demonstrated that, see §7.1.1 in The Paper. See also discussion in our paper on the cooling fraction at high redshifts.

Won't you miss high-redshift clusters if there are bright AGNs in the center?

We've studied this effect as well (§6.5 in The Paper). Detection efficiency is decreased significantly only if the AGN is approximately a factor of 2–3 more luminous than the host cluster. The effect on the flux estimate is more significant (basically, from ROSAT data we derive a total luminosity of the AGN+cluster system). However, we have Chandra data for all clusters we use in the cosmological work and so we can remove any contribution from point sources (it was never found to be significant).