INTERACTION VERSUS RADIO-SOURCE GENERATION - THE PROPERTIES OF RADIO JET PARENT GALAXIES

A sample of 47 galaxies with radio jets from the Bridle and Perley list with z ≤ 0.15 and δ ≥ -15° has been observed with CCD two-dimensional imaging (Colina and Pérez-Fournon). As much as 50% of the sample presents morphological peculiarities like isophote twists, nonconcentric isophotes, filaments, or a large companion galaxy present. This fraction agrees with previous values obtained for high-luminosity radio galaxies (Hutchings; Heckman et al.). Considering projection effects, at least 35% of the radio jet galaxies are undergoing physical interaction with another elliptical galaxy. Of the present sample, 45% of the galaxies (21) are classified as dumbbell (six) or have a companion galaxy, mean relative size 0.37 that of the radio source, at projected distances shorter than 20 kpc (15). These galaxies, the multicomponent sample, present a very homogeneous set of radio properties: 67% have 22.0 ≤ log P5 GHzcore ≤ 23.0 WHz-1; 67% have 24.0 ≤ log P1.4 GHztotal ≤ 25.0 WHz-1; 67% have 10 ≤ djet ≤ 40 kpc; 71% have 0.00 ≤ P5core/P1.4total ≤ 0.03. A parameterization of the companion galaxies within 20 kpc of the radio galaxy nucleus is done in terms of number, size, and gravitational potential. The rest of the sample, consisting of galaxies with no companions at distances shorter than 20 kpc, isolated sample, appears as more heterogeneous, with a large fraction presenting characteristics of gas-rich galaxies. We conclude that multicomponent galaxies are associated with physical interaction between elliptical galaxies, e.g., 3C 465, 3C 278, or B2 0206 + 35. On the other hand, our isolated galaxies are most likely associated with gas-rich galaxies, e.g., 3C 120, with interactions/merging involving gas-rich galaxies, e.g., 3C 305, or with elliptical galaxies, some of them showing a very compact core, e.g., 3C 303 or 3C 371. The differences in the radio properties are explained as a consequence of a different optical parent galaxy population and interaction effects. Galaxies with gas produce more powerful radio sources than those without. Also, interactions seem to control, at least when ellipticals are involved, the process of energy generation, producing a very well defined class of radio sources.