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arXiv · 2606.16343

Optical Variability as a Probe of Hidden Nuclear Activity in Type 2 AGNs

Maša Lakićević
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Abstract

Optical variability in Type 2 active galactic nuclei (AGNs) is rarely explored because the direct accretion-disk continuum is obscured by circumnuclear dust. Nevertheless, detectable optical variations are present in multi-epoch surveys such as SDSS Stripe~82, indicating that some component of the nuclear emission is observed indirectly, for example through scattering or partial transmission. This study explores whether this variability is statistically connected to spectroscopic parameters of the narrow-line region (NLR), using the ALPAKA catalogue of spectral measurements. A subsample of 412 Type 2 AGNs was assembled by crossmatching SDSS Stripe 82 multi-epoch variability measurements in the $u,g,r,i,z$ bands with the ALPAKA spectroscopic catalogue. Correlations were then computed between the root-mean-square (RMS) variability amplitudes and the corresponding emission-line luminosities, kinematic widths and equivalent widths (EWs). Significant anti-correlations are found between the RMS amplitudes and [O III] 4949, [O III] 5007, [N II] 6548 and [NII] 6584 line luminosities. Velocity dispersions ($\sigma$) and EWs of forbidden-lines [O III] 5007 and [N II] 6584 also show moderate anti-correlations with RMS. The results demonstrate that even in obscured AGNs, optical variability carries information about the hidden nucleus. The anti-correlation between RMS and line luminosity suggests a connection between accretion stability and ionising output. Anti-correlations between RMS and the [O III] and [N II] velocity dispersions indicate a secondary correlation between optical RMS variability and the integrated kinematic state of the NLR. In addition, the anti-correlation between RMS and EW shows that the EW variations are primarily driven by changes in the continuum level, while the narrow-line flux itself remains effectively constant on the relevant timescales.

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Maša Lakićević. 2026-06-15. Optical Variability as a Probe of Hidden Nuclear Activity in Type 2 AGNs. https://doi.org/10.1051/0004-6361%2F202558342

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