CACCIANIGA, AlessandroAlessandroCACCIANIGADallacasa, D.D.DallacasaAntón, S.S.AntónBallo, L.L.BalloBerton, M.M.BertonMack, K. -H.K. -H.MackPaulino-Afonso, A.A.Paulino-Afonso2020-08-252020-08-2520170035-8711http://hdl.handle.net/20.500.12386/26799We present very long baseline interferometry (VLBI) observations, carried out with the European Very Long Baseline Interferometry Network (EVN), of SDSSJ143244.91+301435.3, a radio-loud narrow-line Seyfert 1 (RL NLS1) characterized by a steep radio spectrum. The source, compact at Very Large Array resolution, is resolved on the milliarcsec scale, showing a central region plus two extended structures. The relatively high brightness temperature of all components (5 × 10<SUP>6</SUP>-1.3 × 10<SUP>8</SUP> K) supports the hypothesis that the radio emission is non-thermal and likely produced by a relativistic jet and/or small radio lobes. The observed radio morphology, the lack of a significant core, and the presence of a low frequency (230 MHz) spectral turnover are reminiscent of the Compact Steep-Spectrum (CSS) sources. However, the linear size of the source (∼0.5 kpc) measured from the EVN map is lower than the value predicted using the turnover/size relation valid for CSS sources (∼6 kpc). This discrepancy can be explained by an additional component not detected in our observations, accounting for about a quarter of the total source flux density, combined to projection effects. The low core dominance of the source (CD < 0.29) confirms that SDSSJ143244.91+301435.3 is not a blazar, I.e. the relativistic jet is not pointing towards the observer. This supports the idea that SDSSJ143244.91+301435.3 may belong to the `parent population' of flat-spectrum RL NLS1 and favours the hypothesis of a direct link between RL NLS1 and compact, possibly young, radio galaxies.STAMPAenArticle10.1093/mnras/stw24712-s2.0-85014730953000393647100016https://academic.oup.com/mnras/article/464/2/1474/22828562017MNRAS.464.1474CFIS/05 - ASTRONOMIA E ASTROFISICA