4. AN EXAMPLE GRAND UNIFICATION SCHEME - OBSERVATIONAL PREDICTIONS

Figure 3 shows two radio-optical planes for Class A and Class B objects in an example grand unification scheme (after Meier 1999). These figures are to be compared with observed radio-optical planes like that of Ledlow & Owen (1996). As the optical luminosity of the galaxy or quasar scales with black hole mass in both cases, the horizontal axis is M_H in both. The vertical axis is the observed radio power using the Bicknell factor to convert L_jet to P^rad. The curves separate the plane into several different black hole spin states: NO sources (j > 1 is not allowed); FR II sources (j_crit < j < 1), FR I sources (j_min < j < j_crit), and radio quiet objects (j < j_min). For j_crit we have used here the generalized magnetic switch of Meier (1999), but Bicknell's FR I/II transonic condition could be substituted. For j_min we have chosen the point where the predicted black hole MHD power in equation (5) equals the thin disk MHD power with B_p = (H/R) B. Other observational definitions of radio quietness (using the radio-optical flux ratio) are shown.

Figure 3. Example of a grand unification scheme (after Meier 1999). Left panel shows Class B objects (e.g., radio galaxies; = 0.01), right panel Class A objects (e.g., quasars; = 0.1). Lines dividing the radio-optical planes are discussed in the text.

This grand unification scheme makes some interesting predictions. There should be a population of sources corresponding to FR I quasars (high , low j). These were formerly FR II sources, but their holes have since spun down. However, the spindown time for Class A sources is so short (equation 7) that it is likely that the FR II hot spots will still be radiating as the source goes through the FR I phase. Such hybrid FR II sources could be identified by young diffuse emission or ``bridges'' between the radio core and the hot spots. The FR IIa quasars identified by R. Daly (these proceedings) are candidates for such sources; the FR IIa/IIb transition also appears to occur near the j = j_crit line in Figure 3b.

There also should be a population of high redshift, faint sub-mJy FR I and II radio sources associated with spiral galaxies or pre-spiral bulges (M_H < 10⁷ M). If the accretion rate was high at that time - the most likely case in the early universe - then these may appear as optically faint radio quasars (L^opt 10⁴³ erg s^-1, P^rad 10^23-27 W Hz^-1). Their numbers should be a significant fraction of the present-day spiral population, exceeding the contribution of quasars residing in elliptical galaxies alone.