Evidence for Rapid Redshift Evolution of Strong Cluster Cooling Flows

TL;DR

This study finds a significant decline in strong cooling flow clusters from redshift 0.5 to the present, suggesting evolution driven by cluster mergers and active galactic nucleus heating.

Contribution

It provides observational evidence for rapid redshift evolution of cluster cooling flows by analyzing nebular emission in brightest cluster galaxies.

Findings

No strong nebular emission detected in the sample

Fewer strong cooling flow clusters at higher redshift

Supports evolution of cooling flows over cosmic time

Abstract

We present equivalent widths of the [OII] and Ha nebular emission lines for 77 brightest cluster galaxies (BCGs) selected from the 160 Square Degree $ROSAT$ X-ray survey. We find no [OII] or Ha emission stronger than -15 angstroms or -5 angstroms, respectively, in any BCG. The corresponding emission line luminosities lie below 6E40 erg/s, which is a factor of 30 below that of NGC1275 in the Perseus cluster. A comparison to the detection frequency of nebular emission in BCGs lying at redshifts above z = 0.35 drawn from the Brightest Cluster Survey (Crawford et al. 1999) indicates that we should have detected roughly one dozen emission-line galaxies, assuming the two surveys are selecting similar clusters in the X-ray luminosity range 10E42 erg/s to 10E45 erg/s. The absence of luminous nebular emission (ie., Perseus-like systems) in our sample is consistent with an increase in the number density of {\it strong} cooling flow (cooling core) clusters between $\rm z=0.5$ and today. The decline in their numbers at higher redshift could be due to cluster mergers and AGN heating.