The merger-driven evolution of warm infrared luminous galaxies

TL;DR

This paper develops a merger-driven evolutionary model for warm infrared luminous galaxies, showing that both star formation and AGN activity contribute to their warm IR colors, with implications for interpreting their observational signatures.

Contribution

The study introduces a comprehensive simulation-based model that links galaxy mergers, star formation, and black hole growth to warm IR colors, highlighting the complex interplay of these processes.

Findings

Warm (U)LIRGs can be produced by gas-rich major mergers with star formation and black hole growth.

Warm IR colors can result from star formation alone, not just AGN activity.

The model aligns with observed IR flux ratios and predicts scatter in IR color at fixed luminosity.

Abstract

We present a merger-driven evolutionary model for the production of luminous (LIRGs) and ultraluminous infrared galaxies (ULIRGs) with warm IR colours. Our results show that simulations of gas--rich major mergers including star formation, black hole growth, and feedback can produce warm (U)LIRGs. We also find that while the warm evolutionary phase is associated with increased AGN activity, star formation alone may be sufficient to produce warm IR colours. However, the transition can be suppressed entirely - even when there is a significant AGN contribution - when we assume a single-phase ISM, which maximizes the attenuation. Finally, our evolutionary models are consistent with the 25-to-60 micron flux density ratio vs. L_HX/L_IR relation for local LIRGs and ULIRGs, and predict the observed scatter in IR color at fixed L_HX/L_IR. Therefore, our models suggest a cautionary note in the interpretation of warm IR colours: while associated with periods of active black hole growth, they are probably produced by a complex mix of star formation and AGN activity intermediate between the cold star formation dominated phase and the birth of a bright, unobscured quasar.