Annu. Rev. Astron. Astrophys. 1994. 32: 277-318 Copyright © 1994 by Annual Reviews. All rights reserved

3.4 Summary of Data from Non-X-Ray Wavebands

Many central galaxies in cooling flows show anomalies, such as strong, low-ionization, emission-line nebulae and diffuse blue light in the optical and high Faraday rotation and/or depolarization in the radio, which together are not seen in non-cooling-flow galaxies. These indicate that something unusual is occurring and are a link to the cooling flow but do not readily reveal the large mass cooling rates, or amounts of cooled gas, found in X rays. The optical anomalies are confined to the inner few kpc of the flow which corresponds to less than one-thousandth of its total volume. The bulk of the flow is undetected at non-X-ray wavelengths. Only a small fraction of the cooled gas can form stars with a normal IMF. Most must remain dark.

Pressures obtained from optical [SII] emission lines and from radio data are consistent with those found from X-ray data, confirming the first-order interpretation of the X-ray results and the short radiative cooling times of the hot gas. Velocity widths of the optical emission lines indicate that at least the inner region of a flow is turbulent.