Ensemble Variability Properties of Active Galactic Nuclei in the SDSS DR17

TL;DR

This study analyzes the variability of approximately 9,600 AGN from SDSS DR17 over various timescales, revealing that accretion rate primarily influences variability amplitude, with anti-correlations extending across a wide luminosity range.

Contribution

It provides the first extensive analysis linking AGN variability to black hole mass and accretion rate across a broad luminosity and redshift range.

Findings

Variability amplitude anti-correlates with luminosity over four orders of magnitude.

Accretion rate is the main factor affecting variability amplitude.

Anti-correlation between black hole mass and variability is strongest at low accretion rates.

Abstract

We present the results from a study of ~9,600 Broad-Line selected AGN with host galaxies detected from the Sloan Digital Sky Survey Data Release 17 (SDSS DR17). We compute ensemble variability statistics based on the comparison of the original SDSS photometric data with spectrophotometric measurements obtained days to decades later in the Sloan g-, r-, and i-bands. Galaxy and AGN templates have been fitted to the SDSS spectra to isolate the AGN component from the host galaxy. The sources have absolute magnitudes in the range -24<M_i<-18 and lie at redshifts less than z~0.9. A variability analysis reveals that the anti-correlation between luminosity and variability amplitude continues down to log(L_bol[erg/s]) = 43.5, demonstrating that the relationship extends by 4 orders of magnitude in AGN luminosity. To further explore the connection between AGN luminosity and variability, we determine the black hole mass and the accretion rate through measurement of the H-Beta line width and the monochromatic luminosity at rest-frame 5,100 angstrom. Our results suggest that the accretion rate is the dominant parameter impacting the amplitude of variability and that the anti-correlation between accretion rate and amplitude extends to rates as low as 1% Eddington. Moreover, we also identify an anti-correlation between variability amplitude and black hole mass, with the correlation appearing strongest among the AGN with low accretion rates.