Is quasar variability regulated by the close environment of accretion?

Abstract

Ultraviolet (UV)/optical variability in quasars is a well-observed phenomenon, yet its primeval origins remain unclear. This study investigates whether the accretion disc turbulence, which is responsible for UV/optical variability, is influenced by the close environment of the accretion by analysing the correlation between variability and infrared emission for two luminous quasar samples from the Sloan Digital Sky Survey (SDSS). The first sample includes light curves from SDSS, Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), and Zwicky Transient Facility 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 (ρrms) and the wavelength-dependent infrared covering factor (LIR(λ)/Lbol), controlling for the effects of redshift, luminosity, and black hole mass. An anticorrelation between two variables is observed in both samples, which is strongest at wavelengths of 2-3 μm but gradually weakenstowardslonger wavelength. Thissuggeststhe 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 disc turbulence.