How similar are narrow-line Seyfert 1 galaxies and high-z type 1 AGN?

M. Berton, E. Järvelä, A. Tortosa, C. Mazzucchelli

First listed 2025-09-03 | Last updated 2025-09-03

Abstract

The recent observations of highly accreting supermassive black holes (SMBH) at very high redshift ($>$4) with the James Webb Space Telescope (JWST) allowed us to shed light for the very first time on the early evolutionary phases of active galactic nuclei (AGN). Perhaps unsurprisingly, several of the physical properties observed in these new objects, including those known as little red dots (LRDs), are closely reminiscent of the low-mass and high-Eddington AGN in the local Universe, and in particular of the class of narrow-line Seyfert 1 (NLS1) galaxies. However, some differences also emerged, likely due to the radically different evolutionary path and the environment where LRDs and NLS1s live. In this work, we review the multiwavelength properties of local NLS1s and compare them with type 1 AGN found at high-$z$, showing that despite some differences, the study of NLS1s can be extremely useful to better understand the extreme accretion physics of high-$z$ quasars and the early stages of AGN evolution.

Short digest

Review draws a line between local narrow-line Seyfert 1s and the newly uncovered z>4 type 1 AGN/LRDs: both host low-mass (∼10^6–10^7 M⊙) black holes accreting near or above Eddington and often show features like steep, variable X-rays and, in a subset, relativistic jets. The authors argue jets can help shed angular momentum in super-Eddington flows, making NLS1s practical analogs for early SMBH growth. Radio examples underscore the wide range from host-dominated star-formation morphologies to blazar-like, large-scale jets. Key caveat: some systematic differences remain, plausibly tied to distinct environments and evolutionary paths at high redshift.

Key figures to inspect

• Fig. 1 (J0713+3820): Inspect the patchy 5.2 GHz morphology and spectral-index map to see circumnuclear star-formation–dominated radio emission in an NLS1, illustrating the host-dominated end of the class.
• Fig. 2 (J0354−1340): The 5.5 GHz map overlaid on the host shows a southern jet reaching ∼94 kpc projected (∼127 kpc deprojected), demonstrating that some NLS1s launch large-scale, blazar-like jets despite low BH masses.
• Fig. 3 (Mrk 783): Compare the very steep-spectrum region SE of the nucleus with the currently active jet to the NE; this juxtaposition highlights aged plasma versus ongoing activity and possible duty-cycle or orientation changes.
• Fig. 4 (J1522+3934): The non-simultaneous radio SED with PL/BPL fits reveals variability and spectral breaks, useful for diagnosing jet dominance, spectral aging, and absorption in radio-loud NLS1s.