A Spitzer/IRS Study of Local Luminous Infrared Galaxies

TL;DR

This study uses Spitzer/IRS to analyze local luminous infrared galaxies, focusing on silicate features, nuclear star formation, and AGN contributions, revealing intermediate silicate absorption and nuclear star formation characteristics.

Contribution

First detailed infrared spectroscopic analysis of local LIRGs highlighting silicate features and nuclear star formation properties compared to ULIRGs.

Findings

LIRGs show intermediate silicate absorption similar to starburst galaxies.

Most LIRGs have nuclear [NeIII]/[NeII] ratios minimized at their centers.

AGN contribution to mid-IR emission in LIRGs is generally low.

Abstract

We present the first results of our program to study a sample of local luminous infrared galaxies (LIRGs, L_IR = 10^11-10^12 L_sun) with the Spitzer infrared spectrograph (IRS). In these proceedings we investigate the behavior of the 9.7 um silicate feature in LIRGs. As opposed to the extreme silicate absorptions observed in ultraluminous infrared galaxies (ULIRGs, L_IR = 10^12-10^13 L_sun), LIRGs exhibit intermediate silicate absorption features, comparable to those of starburst galaxies. We also find that most of the LIRGs have the minima of the [NeIII]/[NeII] ratio located at their nuclei. It is likely that increased densities in the nuclei are responsible for the smaller nuclear ratios. In the nuclei, it is also possible that the most massive stars are either absent, or still embedded in ultracompact HII regions. Finally we discuss the possible contribution of an AGN to the nuclear mid-IR emission of the galaxy, which in general is low in these local LIRGs.