With two groups of BLRGs it might seem that the unification schemes no longer apply. However, there is an historical pitfall. In the past, an active galaxy was classified as a radio galaxy when the optical galaxy was visible. When it was only a point-like source, it would be called a quasi-stellar object. The names stuck, but with present day instruments, there are many QSRs with visible host galaxies. Also, nearby quasars would have been classified as BLRG. A radio study reveals that there are indeed two groups of BLRGs, one consisting of low-luminosity quasar counterparts and another of mis-oriented quasars. Only the last group are BLRGs which fit into unified models (Dennett-Thorpe et al. 2000). In the sample with 25 µm peakers, there might be more of the first group, while the comparison sample consists mostly of objects from the second group. This does not contradict unified models, but it shows that there is more to it than just orientation.
5.2. Nuclear and extended dust
In the HST images the peakers lack extended dust related to star-formation, but there is no clear evidence that a central torus is absent as well. The fact that the broad-line region is visible indicates that the torus could be smaller in these objects. In the classical unification schemes there might be confusion between obscuration of the central parts by a nuclear torus, or by extended dust in the host galaxy. There is no easy way to tell the difference between these two geometries, but it implies that NLRG without extended dust could appear as BLRG, irrespective of the presence of a nuclear dust torus.
There might be an evolutionary link between 25 µm peakers and normal BLRGs. Dust is the main fuel for both star-formation and the AGN, but there is a limited supply. Especially when the galaxy is isolated, there are no ways to re-fuel the host galaxy and star-formation will cease. When the fuel for the AGN runs out as well, one expects to see weaker emission lines and lower radio power. In addition, without extended dust, these galaxies should have little reddening and low polarization. Studies of the polarization, colors, stellar populations and X-ray absorption columns will provide more clues on the nature of the peakers.
Hes et al. (1995) show that there is a correlation between 178 MHz power and 60 µm power, which would imply that the AGN heats the cold dust. However, this work indicates that in many objects the 60 µm dust is related to star-formation processes, as in star-burst galaxies. Combining both results, there could be a relation between the star-formation rate in the host galaxy and the power of the AGN. If one can confirm this relation in larger samples, it will provide important insights in the formation and evolution of both the host galaxy and the central black hole.