A survey of dual active galactic nuclei in simulations of galaxy mergers: frequency and properties

TL;DR

This survey analyzes the frequency and properties of dual active galactic nuclei in galaxy mergers using high-resolution simulations, revealing how merger parameters influence dual AGN activity and observability.

Contribution

It provides a comprehensive simulation-based analysis of dual AGN triggering, observability timescales, and the effects of merger characteristics, filling gaps in understanding their occurrence and detection.

Findings

Dual activity peaks before merger remnant formation at high luminosities.

Dual AGN activity lasts 20-70 Myr in minor mergers and 100-160 Myr in major mergers.

Fraction of dual AGN in merging galaxies is 20-30% for major and 1-10% for minor mergers.

Abstract

We investigate the simultaneous triggering of active galactic nuclei (AGN) in merging galaxies, using a large suite of high-resolution hydrodynamical simulations. We compute dual-AGN observability time-scales using bolometric, X-ray, and Eddington-ratio thresholds, confirming that dual activity from supermassive black holes (BHs) is generally higher at late pericentric passages, before a merger remnant has formed, especially at high luminosities. For typical minor and major mergers, dual activity lasts ~20-70 and ~100-160 Myr, respectively. We also explore the effects of X-ray obscuration from gas, finding that the dual-AGN time decreases at most by a factor of ~2, and of contamination from star formation. Using projected separations and velocity differences rather than three-dimensional quantities can decrease the dual-AGN time-scales by up to ~4, and we apply filters which mimic current observational-resolution limitations. In agreement with observations, we find that, for a sample of major and minor mergers hosting at least one AGN, the fraction harbouring dual AGN is ~20-30 and ~1-10 per cent, respectively. We quantify the effects of merger mass ratio (0.1 to 1), geometry (coplanar, prograde, retrograde, and inclined), disc gas fraction, and BH properties, finding that the mass ratio is the most important factor, with the difference between minor and major mergers varying between factors of a few to orders of magnitude, depending on the luminosity and filter used. We also find that a shallow imaging survey will require very high angular resolution, whereas a deep imaging survey will be less resolution-dependent.