Abstract
Narrow-line Seyfert 1 (NLS1) galaxies are active galactic nuclei (AGN) believed to be in the early stages of their evolution. A fraction of them have been found to host relativistic jets. Due to the lack of large-scale diffuse radio emission they are believed to be experiencing one of their first activity cycles, and can offer us an opportunity to study the early evolution of more powerful AGN, such as radio galaxies and flat-spectrum radio quasars. Recently, a group of intriguing jetted NLS1s was discovered: based on high radio frequency data they host relativistic jets, but in the JVLA observations they all showed steep radio spectra at least up to 9.0 GHz, indicating very strong absorption at these frequencies. In this paper we study a subset of these sources in detail by employing spatially resolved radio spectral index maps at central frequencies of 1.6, 5.2, and 9.0 GHz. With spectral index maps we can disentangle the different radio emission components over the radio-emitting region, and get insights into the production mechanisms of radio emission. In addition, we study their host galaxies in relation to the radio emission to investigate if the host can provide us additional information regarding the origin of the radio emission, or the launching mechanism of the jets. It is fascinating how different the sources studied are, and certainly more, especially wide frequency-range, and high-resolution observations will be needed to understand their history and current properties, such as the reason behind the extraordinary radio spectra.
Highlights
Narrow-line Seyfert 1 (NLS1) galaxies are a class of young active galactic nuclei (AGN) that are extremely interesting from the point of view of AGN evolution (Mathur, 2000)
We especially focus on their host galaxies in connection to the radio emission, as it can help us understand the origin of the radio emission, and possibly the launching mechanism of the jets in these sources, as jetted NLS1s have found to often reside in interacting galaxies (Antón et al, 2008; Järvelä et al, 2018)
Based on the 90° mismatch between the host and the extended radio emission in J1522 + 3934, and its flat core, it seems safe to assume that the AGN is the origin of almost all radio emission seen in this source
Summary
Narrow-line Seyfert 1 (NLS1) galaxies are a class of young active galactic nuclei (AGN) that are extremely interesting from the point of view of AGN evolution (Mathur, 2000). In their optical spectrum the permitted lines are of comparable width to their forbidden lines, and they are defined based on this property: by definition, the full-width at half maximum of the broad Hβ, FWHM(Hβ) < 2,000 km s−1 (Osterbrock and Pogge, 1985). Since the bolometric luminosities of Absorbed Jets in NLS1s
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