A comprehensive radio study of narrow-line Seyfert 1 galaxies

Narrow-line Seyfert 1 (NLS1) galaxies are a type of active galactic nuclei (AGN) that were originally 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 biggest curiosities found in these sources is their ability to form and maintain powerful relativistic jets. We studied the radio properties of a sample of 3998 NLS1 galaxies which is the largest clean sample available, thus allowing us to study the population-wide characteristics. We used both historical and ongoing surveys: the LOw-Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS; 144~MHz), the Faint Images of the Radio Sky at Twenty-centimeters (FIRST; 1.4~GHz), the National Radio Astronomy Observatory (NRAO) Very Large Array (VLA) Sky Survey (NVSS; 1.4~GHz), and the VLA Sky Survey (VLASS; 3~GHz). We were able to obtain a radio detection for $\sim40\%$ of our sources, with the most detections by LoTSS. The majority of the detected NLS1 galaxies are faint ($\sim1-2$ 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 and lays the foundation for targeted future studies.