Long-slit spectroscopy of gas in the cores of X-ray luminous clusters

The authors report the results of long-slit spectroscopy obtained for the core regions of 14 clusters of galaxies. Seven of these clusters have optical emission in their cores. The presence of the optical emission is shown to depend on whether the central density of the hot X-ray emitting gas exceeds a critical value of roughly 8×10-3h1/2cm-3 h = H0/(100 km s-1Mpc-1). This result is naturally understood in terms of the "radiative regulation" model, where the hot gas cools and accretes to form the optical systems. It is argued that the emission is shock-excited by shocks in the range 70 - 90 km s-1 and that abundances in the gas of O, N, and S are near-solar. Most of the emission in the clusters is confined within 10 h-1kpc or less of the nucleus of the dominant central galaxy.