Galaxy Mergers Drive Shocks: an Integral Field Study of GOALS galaxies

TL;DR

This study uses integral field spectroscopy to analyze shock excitation in 27 nearby luminous infrared galaxies, revealing that shocks become more prominent as galaxy mergers progress, significantly contributing to their emission lines.

Contribution

It provides a detailed spatial and kinematic analysis of shock excitation in U/LIRGs, highlighting the increasing role of shocks during galaxy mergers.

Findings

Widespread shock excitation observed in many U/LIRGs.

Shock contribution to Hα luminosity increases with merger stage.

Shocks may account for up to half of the Hα emission in late-stage mergers.

Abstract

We present an integral field spectroscopic study of radiative shocks in 27 nearby ultraluminous and luminous infrared galaxies (U/LIRGs) from the Great Observatory All-sky LIRG Survey, a subset of the Revised Bright Galaxy Sample. Our analysis of the resolved spectroscopic data from the Wide Field Spectrograph (WiFeS) focuses on determining the detailed properties of the emission line gas, including a careful treatment of multi- component emission line profiles. The resulting information obtained from the spectral fits are used to map the kinematics of the gas, sources of ionizing radiation and feedback present in each system. The resulting properties are tracked as a function of merger stage. Using emission line flux ratios and velocity dispersions, we find evidence for widespread, extended shock excitation in many local U/LIRGs. These low-velocity shocks become an increasingly important component of the optical emission lines as a merger progresses. We find that shocks may account for as much as half of the H{\alpha} luminosity in the latest-stage mergers in our sample. We discuss some possible implications of our result and consider the presence and effects of AGN on the spectra in our sample.