The phylogeny of quasars and the ontogeny of their central black holes
  The connection between multifrequency quasar observational and physical
parameters related to accretion processes is still open to debate. In the last
20 year, Eigenvector 1-based approaches developed since the early papers by
Boroson and Green (1992) and Sulentic et al. (2000b) have been proven to be a
remarkably powerful tool to investigate this issue, and have led to the
definition of a quasar "main sequence". In this paper we perform a cladistic
analysis on two samples of 215 and 85 low-z quasars (z 0.7) which were studied
in several previous works and which offer a satisfactory coverage of the
Eigenvector 1-derived main sequence. The data encompass accurate measurements
of observational parameters which represent key aspects associated with the
structural diversity of quasars. Cladistics is able to group sources radiating
at higher Eddington ratios, as well as to separate radio-quiet (RQ) and
radio-loud (RL) quasars. The analysis suggests a black hole mass threshold for
powerful radio emission and also properly distinguishes core-dominated and
lobe-dominated quasars, in accordance with the basic tenet of RL unification
schemes. Considering that black hole mass provides a sort of "arrow of time" of
nuclear activity, a phylogenetic interpretation becomes possible if cladistic
trees are rooted on black hole mass: the ontogeny of black holes is represented
by their monotonic increase in mass. More massive radio-quiet Population B
sources at low-z become a more evolved counterpart of Population A i.e., wind
dominated sources to which the "local" Narrow-Line Seyfert 1s belong.
