Are Boltzmann Plots of Hydrogen Balmer lines a tool for identifying a
  subclass of S1 AGN?
  It is becoming clear that we can define two different types of nearby AGN
belonging to the Seyfert 1 class (S1), on the basis of the match of the
intensities of their Broad Balmer Lines (BBL) with the Boltzmann Plots (BP).
These two types of S1 galaxies, that we call BP-S1 and NoBP-S1, are
characterized, in first approximation, by Broad Line Regions (BLR) with
different structural and physical properties. In this communication, we show
that these features can be well pointed out by a multi-wavelength analysis of
the continuum and of the broad recombination Hydrogen lines, that we carry out
on a sample of objects detected at optical and X-ray frequencies. The
investigation is addressed to verify whether BP-S1 are the ideal candidates for
the study of the kinematical and structural properties of the BLR, in order to
derive reliable estimates of the mass of their central engine and to constrain
the properties of their nuclear continuum spectrum.
