Revised optical classification of a sample of gamma-ray emitting AGN with GTC and VLT

TL;DR

This study refines the optical classifications of a sample of γ-ray emitting AGN using new GTC/OSIRIS and VLT/FORS2 spectra, identifying two new γ-ray NLS1s and clarifying several IS and Ambiguous cases. By deriving black hole masses from Hβ-based virial relations (with preference for the line width σ_Hβ) and estimating bolometric luminosities from line proxies to mitigate jet contamination, the authors find BH masses spanning roughly $10^{6.25}$ to $10^{9.32}$ M$_ _ _$ and Eddington ratios from about $0.05$ to $2.07$, with some upper limits extending higher. The results reinforce that powerful relativistic jets can be produced by AGN with relatively small BH masses and demonstrate the continued importance of high-quality optical spectroscopy to accurately classify γ-ray emitters. Overall, the γ-NLS1 population appears as a significant and growing component of the γ-ray AGN landscape, influencing our understanding of jet formation and the blazar main sequence.

Abstract

We report the results of the optical follow-up of a sample of $γ$-ray-emitting active galactic nuclei (AGN). New high-quality optical spectra were obtained using Gran Telescopio Canarias with Optical System for Imaging and low- Intermediate-Resolution Integrated Spectroscopy and the European Southern Observatory Very Large Telescope Unit Telescope 1 with the FOcal Reducer and low dispersion Spectrograph 2. From the analysis of these spectra, we confirmed the previous classification as narrow-line Seyfert 1 (NLS1) for four objects and discovered two new NLS1s, bringing the total number of optically confirmed $γ$-NLS1s to 26. We also identified two ambiguous cases between NLS1 and intermediate Seyfert (IS), three IS, one broad-line Seyfert 1, one Seyfert 2. Based on the new spectra, we calculated black hole masses ranging from $10^{6.25}$ to $10^{9.32}$ $M_\odot$, and Eddington ratios spanning 0.05 to 2.07. This reclassification reinforces the scenario in which AGN with relatively small black hole masses are capable of launching powerful relativistic jets, contributing to our broader understanding of $γ$-ray-emitting AGN.

Figures (5)

• Figure 1: Pie chart showing the distribution of different source classes in the 4FGL catalog. Percentages indicate the updated number of objects in each class, based on 2022Univ....8..587F and revised according to the analysis presented in this work and other recent studies. Specifically, 2980 sources are from 2022Univ....8..587F, two (J0105$+$1912 and J0933$-$0013) from 2024MNRAS.527.7055P, and one (J0959$+$4600) from 2023AA...676A...9L.
• Figure 2: FWHM(H$\beta_{\rm broad}$)--$R_{4570}$ plane defining the quasar MS. The same plot shows pop. A and B, together with their finer subdivisions. Shaded regions indicate the areas populated by quasars, with color intensity representing the source density in each region. The pink points represent the objects in the current sample for which the FWHM(H$\beta_{\rm broad}$) and $R_{4570}$ were measured.
• Figure 3: Continued on the next page. Spectra of the considered sources. Top panels: redshift-corrected spectra with continuum and iron line fits overlaid. Grey dotted rectangles indicate the regions that are magnified in the lower panels, where detailed line fitting is performed. Bottom panels: fitted emission lines (e.g., H$\beta$--[O III]$\lambda\lambda$4959,5007 or Mg II$\lambda2800$--[O II]$\lambda3727$), along with the corresponding residuals.
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