SDSSJ143244.91+301435.3 at VLBI: a compact radio galaxy in a narrow-line Seyfert 1

• Published in: Monthly notices of the Royal Astronomical Society Vol. 464; no. 2; p. 1474
• Main Authors: Caccianiga, A, Dallacasa, D, Anton, S, Ballo, L, Berton, M, Mack, K-H, Paulino-Afonso, A
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 11.01.2017
• Subjects: Arrays; Dominance; Interferometry; Networks; Quasars; Radio; Radio galaxies; Radio sources (astronomy); Radio telescopes; Seyfert galaxies; Spectrum analysis; Star maps; Stars & galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw2471

We 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 x 10 super( 6)-1.3 x 10 super( 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 (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.