Dependence of the optical/UV variability on the emission line properties and Eddington ratio in active galactic nuclei

TL;DR

This study investigates how optical/UV variability in radio-quiet AGNs relates to spectral properties and Eddington ratio, revealing that variability is smaller in NLS1s and inversely correlated with Eddington ratio, emphasizing the role of accretion disks.

Contribution

It provides new evidence linking optical/UV variability to Eddington ratio and emission line properties, highlighting the importance of accretion disks in AGN variability.

Findings

NLS1 AGNs show smaller variability than BLS1 AGNs.

Variability correlates with Eigenvector 1 spectral parameters.

Inverse correlation between variability and Eddington ratio.

Abstract

The dependence of the long-term optical/UV variability on the spectral and the fundamental physical parameters for radio-quiet active galactic nuclei (AGNs) is investigated. The multi-epoch repeated photometric scanning data in the Stripe-82 region of the Sloan Digital Sky Survey (SDSS) are exploited for two comparative AGN samples (mostly quasars) selected therein, a broad-line Seyfert\,1 (BLS1) type sample and a narrow-line Seyfert\,1 (NLS1) type AGN sample within redshifts 0.3--0.8. Their spectral parameters are derived from the SDSS spectroscopic data. It is found that on rest-frame timescales of several years the NLS1-type AGNs show systematically smaller variability compared to the BLS1-type. In fact, the variability amplitude is found to correlate, though only moderately, with the Eigenvector\,1 parameters, i.e., the smaller the \hb\ linewidth, the weaker the [O\,III] and the stronger the \feii\ emission, the smaller the variability amplitude is. Moreover, an interesting inverse correlation is found between the variability and the Eddington ratio, which is perhaps more fundamental. The previously known dependence of the variability on luminosity is not significant, and that on black hole mass---as claimed in recent papers and also present in our data---fades out when controlling for the Eddington ratio in the correlation analysis, though these may be partly due to the limited ranges of luminosity and black hole mass of our samples. Our result strongly supports that an accretion disk is likely to play a major role in producing the opitcal/UV variability.