A comprehensive radio study of narrow-line Seyfert 1 galaxies

¹ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, FI-02540 Kylmälä, Finland
² Aalto University Department of Electronics and Nanoengineering, P.O. Box 15500 FI-00076 Aalto, Finland
³ Department of Physics and Astronomy, Texas Tech University, Box 41051 Lubbock, 79409-1051 TX, USA
⁴ Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, 440 W. Brooks St., Norman, OK 73019, USA
⁵ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁶ Private Researcher, Raisio, Finland

^⋆ Corresponding author: irene.varglund@aalto.fi

Received: 1 June 2024
Accepted: 23 September 2025

Abstract

Narrow-line Seyfert 1 (NLS1) galaxies are a type of active galactic nuclei (AGNs) that had originally been classified as sources with little to no radio emission. Although the class is rather unified from an optical perspective, their radio characteristics are diverse. One of the most curious aspects of these sources is their ability to form and maintain powerful relativistic jets. In this work, we studied the radio properties of the cleanest available sample of 3998 NLS1 galaxies, which allowed us to investigate the population-wide characteristics. We used both historical and ongoing surveys: LOw-Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS; 144 MHz), Faint Images of the Radio Sky at Twenty-centimeters (FIRST; 1.4 GHz), National Radio Astronomy Observatory (NRAO) Very Large Array (VLA) Sky Survey (NVSS; 1.4 GHz), and VLA Sky Survey (VLASS; 3 GHz). We were able to obtain a radio detection for ∼40% of our sources, with the largest number of detections provided by LoTSS. The majority of the detected NLS1 galaxies are faint (∼1 − 2 mJy) and non-variable, suggesting considerable contributions from star formation activities, especially at 144 MHz. However, we identified samples of extreme sources, for example, in fractional variability and radio luminosity, indicating significant AGN activity. Our results highlight the heterogeneity of the NLS1 galaxy population in radio, laying the foundation for targeted future studies.