The aim of this work is to understand the nature of the parent population of beamed narrow-line Seyfert 1 galaxies (NLS1s), by studying the physical properties of three parent candidates samples: steepspectrum radio-loud NLS1s, radio-quiet NLS1s and disk-hosted radiogalaxies.
In particular, we focused on the black hole mass and Eddington ratio distribution and on the interactions between the jet and the narrowline region.