Dwarf AGNs from Variability for the Origins of Seeds (DAVOS): Optical Variability of Broad-line Dwarf AGNs from the Zwicky Transient Facility

TL;DR

This study analyzes optical variability in low-mass AGNs using Zwicky Transient Facility data, confirming the relation between black hole mass and variability timescale, and demonstrating potential for detecting intermediate-mass black holes.

Contribution

It expands the $M_{BH} - \tau_{DRW}$ relation to 78 new low-mass AGNs, validating virial black hole mass estimates and highlighting the potential for IMBH detection in future surveys.

Findings

Confirmed the $M_{BH} - \tau_{DRW}$ relation with 78 new low-mass AGNs.

The optical variability timescale correlates with black hole mass, consistent with previous studies.

Intermediate-mass black holes may have variability timescales of tens of hours, aiding their detection.

Abstract

We study the optical variability of a sample of candidate low-mass (dwarf ang Seyfert) active galactic nuclei (AGNs) using Zwicky Transient Facility g-band light curves. Our sample is compiled from broad-line AGNs in dwarf galaxies reported in the literature with single-epoch virial black hole (BH) masses in the range $M_{\rm{BH}} \sim 10^{4}$--$10^{8}\ M_{\odot}$. We measure the characteristic ``damping'' timescale of the optical variability $\tau_{\rm{DRW}}$, beyond which the power spectral density flattens, of a final sample of 79 candidate low-mass AGNs with high-quality light curves. Our results provide further confirmation of the $M_{\rm{BH}} - \tau_{\rm{DRW}}$ relation from Burke et al. 2022 within $1\sigma$ agreement, adding 78 new low-mass AGNs to the relation. The agreement suggests that the virial BH mass estimates for these AGNs are generally reasonable. We expect that the optical light curve of an accreting intermediate-mass black hole (IMBH) to vary with a rest-frame damping timescale of $\sim$ tens of hours, which could enable detection and direct mass estimation of accreting IMBHs in wide-field time-domain imaging surveys with sufficient cadence like with the Vera C. Rubin Observatory.