Composite Spectra in Merging U/LIRGs Caused by Shocks
Abstract
We present a key result from our optical integral field spectroscopic survey of 27 nearby ultra luminous and luminous infrared galaxies (U/LIRGs) from the Great Observatory All-sky LIRG Survey. Using spatially resolved multi-component emission line fitting to trace the emission line ratios and velocity dispersion of the ionized gas, we quantify for the first time the widespread shock ionization in gas-rich merging U/LIRGs. Our results show a fractional contribution to the total observed \Ha flux from radiative shocks increasing from a few percent during early merger stages to upwards of 60% of the observed optical emission line flux in late stage mergers. We compare our resolved spectroscopy to nuclear spectra and find that 3/4 of the galaxies in our sample that would be classified as "composite" based on optical spectroscopy are primarily characterized by a combination of star formation and merger-driven shocks. Our results have important implications for the interpretation of "composite" rest-frame optical spectra of U/LIRGs as starburst+AGN, as the shock emission combined with star formation can mimic "composite" optical spectra in the absence of any contribution from an AGN.
Keywords
Cite
@article{arxiv.1310.3441,
title = {Composite Spectra in Merging U/LIRGs Caused by Shocks},
author = {Jeffrey A. Rich and Lisa J. Kewley and Michael A. Dopita},
journal= {arXiv preprint arXiv:1310.3441},
year = {2015}
}
Comments
Accepted for Publication in ApJ Letters 5 Pages, 4 figures