Rare Occasions: Tidal Disruption Events Rarely Power the AGNs Observed in Dwarf Galaxies

TL;DR

This study analyzes the variability of dwarf galaxy AGNs over 16 years to determine the role of tidal disruption events, finding they rarely power the observed AGNs, contrary to some theoretical predictions.

Contribution

The paper provides the first extensive variability analysis of dwarf galaxy AGNs, using Bayesian methods to constrain the TDE contribution to their activity.

Findings

TDEs are rare among dwarf galaxy AGNs, with an estimated contribution below 10%.

Most dwarf galaxy AGNs are not powered by TDEs, challenging previous theoretical assumptions.

The study introduces a Bayesian framework for assessing TDE prevalence in AGN populations.

Abstract

Tidal disruption events (TDEs) could be an important growth channel for massive black holes in dwarf galaxies. Theoretical work suggests that the observed active galactic nuclei (AGNs) in dwarf galaxies are predominantly TDE-powered. To assess this claim, we perform variability analyses on the dwarf-hosted AGNs detected in the $7$ Ms Chandra Deep Field-South (CDF-S) survey, with observations spanning $\approx 16$ years. Based on the spectral energy distribution (SED) modeling with X-CIGALE, we select AGNs hosted by dwarf galaxies (stellar mass below $10^{10}\ M_\odot$). We focus on X-ray sources with full-band detections, leading to a sample of $78$ AGNs (0.122 $\leq$ $z$ $\leq$ 3.515). We fit the X-ray light curves with a canonical TDE model of $t^{-5/3}$ and a constant model. If the former outperforms the latter in fitting quality for a source, we consider the source as a potential TDE. We identify five potential TDEs, constituting a small fraction of our sample. Using true- and false-positive rates obtained from fitting models to simulated light curves, we perform Bayesian analysis to obtain the posterior of the TDE fraction for our sample. The posterior peaks close to zero ($2.56\%$), and we obtain a $2$-$\sigma$ upper limit of $9.80\%$. Therefore, our result indicates that the observed AGNs in dwarf galaxies are not predominantly powered by TDEs.