SDSSJ143244.91+301435.3: a link between radio-loud narrow-line Seyfert 1
  galaxies and compact steep-spectrum radio sources?
  We present SDSSJ143244.91+301435.3, a new case of radio-loud narrow line
Seyfert 1 (RL NLS1) with a relatively high radio power (P1.4GHz=2.1x10^25 W
Hz^-1) and large radioloudness parameter (R1.4=600+/-100). The radio source is
compact with a linear size below ~1.4 kpc but, contrary to most of the RL NLS1
discovered so far with such a high R1.4, its radio spectrum is very steep
(alpha=0.93) and not supporting a 'blazar-like' nature. Both the small mass of
the central super-massive black-hole and the high accretion rate relative to
the Eddington limit estimated for this object (3.2x10^7 Msun and 0.27,
respectively, with a formal error of ~0.4 dex on both quantities) are typical
of the class of NLS1. Through a modeling of the spectral energy distribution of
the source we have found that the galaxy hosting SDSSJ143244.91+301435.3 is
undergoing a quite intense star-formation (SFR=50 Msun y^-1) which, however, is
expected to contribute only marginally (~1 per cent) to the observed radio
emission. The radio properties of SDSSJ143244.91+301435.3 are remarkably
similar to those of compact steep spectrum (CSS) radio sources, a class of AGN
mostly composed by young radio galaxies. This may suggest a direct link between
these two classes of AGN, with the CSS sources possibly representing the
misaligned version (the so-called parent population) of RL NLS1 showing blazar
characteristics.
