Optical emission-line gas associated with dominant cluster galaxies

A representative sample of 13 dominant cluster galaxies is investigated to determine the presence of the type of emission-line region seen around M87 and NGC 1275. Half of the sample shows detectable emission lines where L(H-alpha + forbidden N III) is greater than 10 to the 40.5th/erg (H₀ = 75). The emission-line luminosity appears to be related to the X-ray luminosity and/or the cluster richness, and a relationship between optical-line and radio emission is found, which indicates that the radio source may help form or excite the emission-line gas. Data are also consistent with the cooling accretion flow picture, which is modified by including the role of the radio source.