Anomalous narrow line Seyfert I galaxies from SDSS DR17

TL;DR

This study analyzes over 22,000 narrow-line Seyfert 1 galaxies from SDSS DR17, identifying spectroscopically anomalous sources and classifying them into distinct groups based on their spectral properties and AGN activity.

Contribution

The paper introduces a novel spectroscopic anomaly detection method (SQuAD) applied to a large NLSy1 sample, revealing intrinsic differences in AGN activity among subclasses.

Findings

Identified 620 anomalous NLSy1s with distinct spectral features.

Classified anomalies into Red, Blue, and Intermediate Seyferts with unique properties.

Discovered that intrinsic AGN activity, not dust or orientation, differentiates NLSy1 subclasses.

Abstract

We present an analysis of 22,656 narrow-line Seyfert 1 galaxies (NLSy1s) from Sloan Digital Sky Survey (SDSS) DR17 ($0.1\leq z\leq 0.9$), identifying a sample of spectroscopically anomalous sources. These anomalies were detected via the spectroscopic quasar anomaly detection (SQuAD) algorithm, which employed principal component analysis and hierarchical k-means clustering. Various physical diagnostic analysis were performed such as the color excess ($E_{(B-V)}$) calculations, Wide-field Infrared Survey Explorer (WISE) color analysis, probing O III, equivalent width as an inclination indicator, the BPT diagram and eigenvector 1 diagram. We detected 620 anomalous NLSy1s classified into two groups i.e. 246, Red NLSy1s, exhibiting host galaxy dominated spectra with a low luminosity active galactic nuclei (AGN) core revealed by the emission line widths. Another set of 374 Blue NLSy1s, strongly luminous galaxies with enhanced AGN activity, bluer continuum as compared to a typical NLSy1 and stronger Fe II emission. Finally, the third group of 257 outliers, identified as Intermediate Seyferts, a class of Seyfert galaxies identified by composite emission profiles, and extremely strong emission lines paired with virtually no continuum. These sources also exhibit rare and high ionization emission lines unseen in any other NLSy1 spectra (e.g. [Ne V]$\lambda3345$, Ne V $\lambda3426$, Ne III $\lambda3869$ etc). We conclude that the differentiating factor between red and blue NLSy1s is not dust obscuration or orientation effect, but intrinsic distinction in AGN activity. The resulting sample is presented as a value-added catalog.