Is quasar variability regulated by the close environment of accretion?

TL;DR

This study finds that the UV/optical variability in quasars is anti-correlated with infrared emission from the dusty torus, suggesting the close environment influences accretion disk turbulence.

Contribution

It provides evidence that the dusty torus environment affects quasar variability, highlighting the role of the close accretion environment in turbulence regulation.

Findings

Anti-correlation between variability and infrared emission at 2-3μm

Dusty torus influences UV/optical variability

Cooler polar dust has less impact on variability

Abstract

UV/optical variability in quasars is a well-observed phenomenon, yet its primeval origins remain unclear. This study investigates whether the accretion disk turbulence, which is responsible for UV/optical variability, is influenced by the close environment of the accretion by analyzing the correlation between variability and infrared emission for two luminous SDSS quasar samples. The first sample includes light curves from SDSS, Pan-STARRS, and ZTF $g$ band photometry, while the second sample utilizes SDSS Stripe 82 $g$ band light curves. We explore the correlation between the $g$ band excess variance ($\sigma_{rms}$) and the wavelength-dependent infrared covering factor ($L_{\rm IR}(\lambda)/L_{\rm bol}$), controlling for the effects of redshift, luminosity, and black hole mass. An anti-correlation between two variables is observed in both samples, which is strongest at wavelengths of 2-3$\mu$m but gradually weakens towards longer wavelength. This suggests the equatorial dusty torus (which dominates near-infrared emission) plays a significant role in influencing the UV/optical variability, while the cooler polar dust (which contributes significantly to mid-infrared emission) does not. The findings indicate that quasar variability may be connected to the physical conditions within the dusty torus which feeds the accretion, and support the notion that the close environment of the accretion plays an important role in regulating the accretion disk turbulence.