Are "Changing-Look" Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and their Hosts? II. The Case of Changing-Look Narrow-Line Seyfert 1 Galaxies

TL;DR

This study investigates the rarity and evolutionary significance of changing-look narrow-line Seyfert 1 galaxies, suggesting they are young AGNs and exploring spectral analysis methods to understand their properties.

Contribution

The paper extends the analysis of changing-look AGNs to NLS1s, confirming their rarity and potential role in AGN evolution, and proposes using off-center SDSS spectra for narrow-line region studies.

Findings

CL-NLS1s are extremely rare, with only three identified in a large sample.

CL-NLS1s tend to be at the young end of the intermediate-old stellar population.

Off-center SDSS spectra can effectively reveal properties of the narrow-line region.

Abstract

The evolutionary role of the so-called ``changing-look'' (CL) active galactic nucleus (AGN), which is characterized by spectral-type transitions within $\sim10$ yr, has been suggested in the past few years. By focusing on CL-AGNs having spectra similar to those of broad-line Seyfert 1 galaxies, some authors have proposed that CL-AGNs tend to be at a special evolutionary stage associated with intermediate-to-old stellar populations. Here we attempt to verify this evolutionary role by extending the sample to CL narrow-line Seyfert 1 (NLS1) galaxies, which are believed to be ``young'' AGNs with a less massive supermassive black hole and high accretion rate. Combining the recent large NLS1 catalog provided by Paliya et al. (2024) and the SDSS-V DR19 spectral survey returns only three CL-NLS1s out of a parent sample of 884 objects, reinforcing the rarity of CL-NLS1s. Subsequent spectral analysis shows that the evolutionary role mentioned above still holds, although CL-NLS1s tend to occupy the young end of the intermediate-old population. Finally, we propose that off-center SDSS spectra caused by the ``fiber drop'' effect have great potential for determining the properties of the narrow-line region of NLS1s.