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SDSS J143244.91+301435.3: a link between radio-loud narrow-line Seyfert 1 galaxies and compact steep-spectrum radio sources?

A. Caccianiga, S. Antón, L. Ballo, D. Dallacasa, R. Della Ceca, F. Fanali, L. Foschini, T. Hamilton, A. Kraus, T. Maccacaro, K.-H Mack, M. Marchã, A. Paulino-Afonso, Eleonora Sani, P. Severgnini

Abstract
We present SDSS J143244.91+301435.3, a new case of a radio-loud narrow-line Seyfert 1 (RL NLS1) with a relatively high radio power (P1.4 GHz = 2.1 × 1025 W Hz-1) and large radio-loudness parameter (R1.4 = 600 ± 100). The radio source is compact with a linear size below ̃1.4 kpc but, in contrast to most of the RL NLS1 discovered so far with such a high R1.4, its radio spectrum is very steep (α = 0.93, Sν ∝ ν) and does not support a `blazar-like' nature. Both the small mass of the central supermassive black hole and the high accretion rate relative to the Eddington limit estimated for this object (3.2 × 107 M and 0.27, respectively, with a formal error of ̃0.4 dex for both quantities) are typical of the NLS1 class. Through modelling the spectral energy distribution of the source, we have found that the galaxy hosting SDSS J143244.91+301435.3 is undergoing quite intense star formation (SFR = 50 M yr-1), which, however, is expected to contribute only marginally (̃1 per cent) to the observed radio emission. The radio properties of SDSS J143244.91+301435.3 are remarkably similar to those of compact steep-spectrum (CSS) radio sources, a class of active galactic nuclei (AGN) mostly composed of young radio galaxies. This may suggest a direct link between these two classes of AGN, with CSS sources possibly representing the misaligned version (the so-called `parent population') of RL NLS1 showing blazar characteristics.

Keywords
galaxies: active – galaxies: nuclei – quasars: individual: SDSS J143244.91 + 301435.3

Monthly Notices of the Royal Astronomical Society
Volume 441, Issue 1, Page 172
2014 April

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Fundação para a Ciência e a Tecnologia
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