The AGN Luminosity Fraction in Merging Galaxies

TL;DR

This study estimates the contribution of active galactic nuclei (AGN) to the infrared luminosity in merging galaxies by analyzing their spectral energy distributions, revealing that AGN contribution increases in later-stage, more luminous mergers.

Contribution

It introduces a comprehensive SED modeling approach to quantify AGN luminosity fractions in merging galaxies across different interaction stages.

Findings

AGN contribution varies from 0% to 91% across systems.

AGN contribution is higher in late-stage, luminous mergers.

Validated SED modeling with simulated mergers and spectral data.

Abstract

Galaxy mergers are key events in galaxy evolution, often causing massive starbursts and fueling active galactic nuclei (AGN). In these highly dynamic systems, it is not yet precisely known how much starbursts and AGN respectively contribute to the total luminosity, at what interaction stages they occur, and how long they persist. Here we estimate the fraction of the bolometric infrared (IR) luminosity that can be attributed to AGN by measuring and modeling the full ultraviolet to far-infrared spectral energy distributions (SEDs) in up to 33 broad bands for 24 merging galaxies with the Code for Investigating Galaxy Emission. In addition to a sample of 12 confirmed AGN in late-stage mergers, found in the $Infrared$ $Array$ $Satellite$ Revised Bright Galaxy Sample or Faint Source Catalog, our sample includes a comparison sample of 12 galaxy mergers from the $Spitzer$ Interacting Galaxies Survey, mostly early-stage. We perform identical SED modeling of simulated mergers to validate our methods, and we supplement the SED data with mid-IR spectra of diagnostic lines obtained with $Spitzer$ InfraRed Spectrograph. The estimated AGN contributions to the IR luminosities vary from system to system from 0% up to 91% but are significantly greater in the later-stage, more luminous mergers, consistent with what is known about galaxy evolution and AGN triggering.