Kiloparsec-Scale Radio Structures in Narrow-Line Seyfert 1 Galaxies

Abstract

We report the finding of kiloparsec (kpc)-scale radio structures in three radio-loud narrow-line Seyfert 1 (NLS1) galaxies from the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) of the Very Large Array (VLA), which increases the number of known radio-loud NLS1s with kpc-scale structures to six, including two γ-ray emitting NLS1s (PMN J0948+0022 and 1H 0323+342) detected by the Fermi Gamma-ray Space Telescope. The detection rate of extended radio emissions in NLS1s is lower than that in broad-line active galactic nuclei (AGNs) with a statistical significance. We found both core-dominated (blazar-like) and lobe-dominated (radio-galaxy-like) radio structures in these six NLS1s, which can be understood in the framework of the unified scheme of radio-loud AGNs that considers radio galaxies as non-beamed parent populations of blazars. Five of the six NLS1s have (i) extended radio luminosities suggesting jet kinetic powers of 10 44 erg s −1 , which is sufficient to make jets escape from hosts' dense environments, (ii) black holes of 10 7 M ⊙ , which can generate the necessary jet powers from near-Eddington mass accretion, and (iii) two-sided radio structures at kpc scales, requiring expansion rates of ∼ 0.01c-0.3c and kinematic ages of 10 7 years. On the other hand, most typical NLS1s would be driven by black holes of 10 7 M ⊙ in a limited lifetime of ∼ 10 7 years. Hence the kpc-scale radio structures may originate in a small window of opportunity during the final stage of the NLS1 phase just before growing into broad-line AGNs.

Properties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

“…Doi et al 2012). One possible explanation, advanced by Doi et al (2012), is that in the case of RLNLS1s, the jet has low kinetic power because of the low mass and because it has to propagate in a gas-rich environment, while in BL Lacs the jet power is slightly greater and develops in a more rarified medium. Another possibility is to invoke the young age of RLNLS1s (Mathur 2000, Mathur et al 2012) and, indeed, many authors made the hypothesis of a link with GPS/CSS sources, which in turn are believed to be very young radio galaxies (Oshlack et al 2001, Komossa et al 2006a, Gallo et al 2006, Yuan et al 2008, Caccianiga et al 2014).…”

“…Estimated jet power from radio core measurements at 15 GHz according to the relationships in Foschini (2014). Columns display the logarithm of the radiative, kinetic (protons, electrons, magnetic field), and total jet powers [erg s Doi et al (2012), such structures might appear only in the sources with greatest black hole masses, which in turn might be in the final stages of their cosmological evolution before changing into broad-line AGNs.…”

“…The emerging characteristics are (a) compact radio morphology, although there are kiloparsec scale structures in some cases (Doi et al 2012), (b) high-brightness temperature of the core feature, indicating nonthermal processes, (c) flat or inverted spectra (although the samples included also steep spectrum radio sources, which are excluded from the present work), and (d) possible links with compact steep spectrum (CSS) and gigahertz peaked spectrum (GPS) radio sources, as also suggested by Oshlack et al (2001) and Gallo et al (2006) for J2007−4434, Komossa et al (2006a), Yuan et al (2008), and more recently by Caccianiga et al (2014). Doi et al (2012) found that the detection of extended emission is lower than expected from broad-line Seyferts and they suggest it could be due to the lower kinetic power of jets in low-mass AGNs, rather than the young age of the source. Interestingly, also the radio core of RQNLS1s and Seyferts display non-thermal characteristics, suggesting some link with jets (Giroletti & Panessa 2009, Doi et al 2013.…”

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447

“…Both paradigms are also discussed for γ-NLS1(e.g., Abdo et al 2009c;Foschini et al 2015;Berton et al 2015), and it has been proposed that CSS and RL-NLS1 are linked (e.g., Komossa et al 2006;Doi et al 2012;Caccianiga et al 2014;Komossa et al 2015;Gu et al 2015). Recently, Caccianiga et al (2015) have found evidence of significant star formation activity in a sample of RL-NLS1s, favouring the scenario that RL-NLS1s are young AGNs.…”

“…We computed the mean T B -value at 15 GHz and ∼8 GHz for the northern γ-NLS1s based on available data from Doi et al (2012), Lister et al (2013), and Foschini et al (2015). In the case of [HB89] 1219+044, the T B value was taken directly from Pushkarev & Kovalev (2012).…”