Investigating the AGN variability timescale -- black hole mass relationship with Gaia, SDSS and ZTF

TL;DR

This study analyzes a large AGN catalog to investigate the relationship between variability timescales and black hole mass, confirming previous correlations and highlighting data quality limitations for precise measurements.

Contribution

It provides a new catalog of AGNs with variability parameters and black hole masses, and assesses the effectiveness of light curve sampling for timescale estimation.

Findings

Confirmed the correlation between variability timescale and black hole mass.

Identified sampling limitations in Gaia light curves for reliable timescale measurement.

Provided a catalog of 127 AGNs with variability and black hole mass data.

Abstract

Active galactic nuclei (AGNs) exhibit variability in their luminosities with timescales that correlate with the mass of the black hole at the centre of the AGN. Presently, the empirical correlation lacks sufficient precision to confidently convert these timescales into black hole masses, especially at the low-mass end. To find more AGNs with timescale measurements, we study a very large catalog of AGNs from the Gaia Data Release 3 called GLEAN (Gaia variabLE AgN; 872228 objects). We identify GLEAN objects with optical spectra from the Sloan Digital Sky Survey DR17 and light curves from the Zwicky Transient Facility (ZTF) DR21. After fitting the light curves with a damped random walk model, we find that the GLEAN light curves have insufficient sampling to extract reliable amplitude and timescale measurements outside the range of 50-100 days. On the other hand, well-sampled ZTF light curves allow more accurate estimations of these parameters. The fractional variability amplitude is an effective, model-independent metric for measuring variability amplitude, but only when derived from high-quality light curves. We provide a catalog of 127 GLEAN AGNs with spectroscopic virial black hole masses, and variability amplitudes and timescales. Though we do not find any low-mass black holes in this AGN sample, we confirm a relationship between the damped random walk timescale and the black hole mass that is consistent with previous studies.