  Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN)
recently identified as a new class of $\gamma$-ray sources. The high energy
emission is explained by the presence of a relativistic jet observed at small
angles, just like in the case of blazars. When the latter are observed at
larger angles they appear as radio-galaxies, but an analogue parent population
for beamed NLS1s has not yet been determined. In this work we analyze this
problem by studying the physical properties of three different samples of
parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s,
and disk-hosted radio-galaxies, along with compact steep-spectrum sources. In
our approach, we first derived black hole mass and Eddington ratio from the
optical spectra, then we investigated the interaction between the jet and the
narrow-line region from the [O III] $\lambda\lambda$4959,5007 lines. Finally,
the radio luminosity function allowed us to compare their jet luminosity and
hence determine the relations between the samples.
