OPTICAL LINE-EMITTING GAS AND RADIO-EMISSION - EVIDENCE FOR CORRELATION IN LOW-LUMINOSITY RADIO GALAXIES

Narrow-band H-alpha + [N II] images of a sample of low-luminosity B2 radio sources are used to investigate the correlations between radio and optical emission-line properties. It is shown that the correlation between radio and emission-line luminosity - previously established for high-power radio galaxies - extends over five decades in radio luminosity and includes the low radio power sources. It is also shown that the compact radio sources have emission-line excesses relative to the other sources in the sample of the same radio power, as well as far-infrared (IR) emission characteristics of emission from cool dust. Although continuity arguments can be used to show that the ionized gas in most of the low-luminosity sources is likely to be photoionized by the Active Galactic Nucleus (AGN), it is possible that additional ionizing sources contribute in the compact, emission-line excess objects. A programme of detailed spectroscopic observations is required to investigate the underlying physical mechanisms in more depth.