Two studies investigate variability in Type 2 active galactic nuclei (AGNs), where dust obscures direct view of the accretion-disk continuum. One work uses optical multi-epoch data from SDSS Stripe 82 combined with the ALPAKA spectroscopic catalog for 412 Type 2 AGNs. It measures variability amplitudes as root-mean-square (RMS) fluctuations in u, g, r, i, and z bands and tests for correlations with properties of the narrow-line region (NLR). The study reports significant anti-correlations between optical RMS variability and the luminosities of several forbidden lines, including [O III] 4949 and 5007 and [N II] 6548 and 6584. It also finds moderate anti-correlations between RMS and velocity dispersions (σ) and equivalent widths for [O III] 5007 and [N II] 6584. The results interpret these trends as evidence that optical variability contains information about the hidden nucleus, with an anti-correlation between RMS and equivalent width suggesting continuum-driven EW changes while narrow-line flux stays roughly constant on the relevant timescales. A second study analyzes near-infrared (NIR) variability using 14-year UltraVISTA data in YJHKs for 533 Type 2 AGNs. It finds that 7–17% are variable in the NIR, with higher variability fractions toward Ks where the dusty torus contributes more. Variability is modeled with a damped random walk process, and NIR variability helps clarify mismatches between optical and X-ray classifications, including identifying weak or misclassified Type 1 AGNs.
Studies link optical and near-infrared variability to hidden activity in Type 2 AGNs
Two studies investigate variability in Type 2 active galactic nuclei (AGNs), where dust obscures direct view of the accretion-disk continuum. One work uses optical multi-epoch data from SDSS Stripe 82...
- Optical variability is detected in Type 2 AGNs despite obscuration, and it correlates with narrow-line-region properties.
- In a sample of 412 Type 2 AGNs, optical RMS variability shows significant anti-correlations with [O III] (4949, 5007) and [N II] (6548, 6584) line luminosities.
- The optical study finds moderate anti-correlations between RMS variability and the velocity dispersions (σ) and equivalent widths of [O III] 5007 and [N II] 6584.
- Near-infrared variability in Type 2 AGNs is measured using 14-year UltraVISTA monitoring; about 7–17% of 533 Type 2 AGNs show NIR variability.
- NIR variability fractions increase toward Ks and are used to flag possible misclassified or weak Type 1 AGNs, with different variability rates reported for X-ray unabsorbed vs. obscured Type 2 samples.
arXiv:2606.16343v1 Announce Type: new 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.
2 hours agoarXiv:2606.15016v1 Announce Type: new Abstract: Near-infrared (NIR) variability studies of active galactic nuclei (AGNs) are still limited, as long-term multiepoch monitoring in the NIR is observationally challenging. The depth, wavelength coverage, and 14-year temporal baseline of UltraVISTA make it one of the few surveys capable of providing a detailed characterization of AGN variability in this regime. We aim to quantify the NIR variability of known AGNs in the COSMOS field and to investigate the physical origin of variability in type 2 AGNs. In particular, we examine how NIR variability can help clarify the discrepancies between optical and X-ray classifications. Using the 14-year multiepoch UltraVISTA DR6 dataset in the YJHKs bands, we constructed calibrated NIR light curves and quantified their variability through a set of metrics. AGN-like stochastic variability was identified by modeling the light curves with a damped random walk (DRW) process. We find that about 7-17% of the 533 type 2 AGNs are variable in the NIR, with variability fractions increasing toward Ks, where the dusty torus dominates the emission. Based on the wavelength dependence of the DRW variability amplitude, we classify variable type 2 AGNs into disk-dominated, torus-dominated, and highly obscured groups. About one third of the X-ray unobscured (XR I) type 2 AGNs are variable in the NIR, consistent with misclassified weak type 1 or true type 2 AGNs. On the other hand, 21.4% (30/140) of the X-ray obscured (XR II) type 2 AGNs show detectable variability in the NIR, most of them only in H or Ks, consistent with obscuration of the bluer (accretion disk) bands. Type 2 AGNs without X-ray counterparts (165) show the smallest fraction (3.6%) of variable objects. NIR variability provides an effective and independent diagnostic for confirming optical classifications and for identifying weak or misclassified type 1 AGNs in deep extragalactic surveys.
2 hours ago
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