We present 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 ( VLA ) resolution , is resolved on the milliarcsec scale , showing a central region plus two extended structures .
The relatively high brightness temperature of all components ( 5 \times 10 ^ { 6 } -1.3 \times 10 ^ { 8 } 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 sources ( CSS ) .
However , the linear size of the source ( \sim 0.5 kpc ) measured from the EVN map is lower than the value predicted using the turnover/size relation valid for CSS sources ( \sim 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 .