The Host Galaxy Fluxes of Active Galaxy Nuclei Are Generally Overestimated by the Flux Variation Gradient Method

Abstract

In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but this assumption has been questioned by the intrinsic color variation of quasars and local Seyfert galaxies. Here, using an up-to-date thermal fluctuation model to simulate multi-wavelength AGN variability, we theoretically demonstrate that the FVG method generally overestimates the host galaxy flux; that is, it is more significant for brighter AGN/quasars. Furthermore, we observationally confirm that the FVG method indeed overestimates the host galaxy flux by comparing it to that estimated through other independent methods. We thus caution that applying the FVG method should be performed carefully in the era of time-domain astronomy.

References in corpus (14)

• The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements
• Quasar Accretion Disks Are Strongly Inhomogeneous
• The Discovery of Timescale-Dependent Color Variability of Quasars
• Reverberation Measurements of the Inner Radii of the Dust Tori in Quasars
• Photometric reverberation mapping of 3C120
• A universal average spectral energy distribution for quasars from optical to extreme ultraviolet
• Optical continuum photometric reverberation mapping of the Seyfert-1 galaxy Mrk509
• Dust Reverberation of 3C273: torus structure and lag -- luminosity relation
• Broadband X-ray/UV/optical time-resolved spectroscopy of NGC 5548: The origin of the UV/optical variability in active galactic nuclei
• Continuum reverberation mapping of MCG 08-11-011
• The H$\alpha$ broadband photometric reverberation mapping of four Seyfert 1 galaxies
• Measurement of AGN dust extinction based on the near-infrared flux variability of WISE data
• Circumstellar Disks revealed by $H$/$K$ Flux Variation Gradients
• On the nature of the continuum reverberation of X-ray/UV and optical emission of IRAS 09149-6206