A comprehensive radio study of narrow-line Seyfert 1 galaxies

TL;DR

This study presents a population-wide radio analysis of 3998 cleanly selected NLS1 galaxies using multi-frequency data from LoTSS (144 MHz), FIRST/NVSS (1.4 GHz), and VLASS (3 GHz). It reveals a broad radio diversity: a large fraction of detections at low frequencies are likely dominated by star formation, while a significant subset shows AGN-driven emission with steep, flat, or inverted spectra and measurable variability, including candidates for CSS/PS-like jets. The work demonstrates substantial heterogeneity in radio luminosity and extendedness, correlating with redshift, Eddington ratio, and black-hole mass, and highlights the impact of survey sensitivity and resolution on inferred properties. While optical properties remain comparatively uniform, the results underscore a complex interplay between star formation and AGN activity in NLS1 galaxies and motivate higher-quality, multiwavelength follow-ups to pin down jet production and host-galaxy contributions.

Abstract

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.

Figures (10)

• Figure 1: Distribution of peak and integrated flux densities. The peak flux density (mJy beam$^{-1}$) is shown in blue and the integrated flux density (mJy) is shown in orange. Top left panel: VLASS Epoch 1, top right panel: VLASS Epoch 2, bottom left panel: FIRST, and bottom right panel: LoTSS All.
• Figure 2: Distribution of NVSS Integrated flux densities in mJy.
• Figure 3: Fractional variability of VLASS
• Figure 4: Left panel: Spectral index plot using 144 MHz and 1.4 GHz v. 1.4 GHz and 3 GHz (Epoch 1), peak flux densities. right panel: Spectral index plot using 144 MHz and 1.4 GHz v. 1.4 GHz and 3 GHz (Epoch 1), integrated flux densities. The average error is plotted with green.
• Figure 5: Left panel: Spectral index plot using 144 MHz and 1.4 GHz v. 1.4 GHz and 3 GHz (Epoch 2), peak flux densities. right panel: Spectral index plot using 144 MHz and 1.4 GHz v. 1.4 GHz and 3 GHz (Epoch 2), integrated flux densities. The average error is plotted with green.