Spitzer/IRS spectra of GOALS luminous IR galaxies

We readily detect emission lines of [SIV], [NeII], [NeV], [NeIII], [SIII]_18.7{mu}m_, [OIV], [FeII], [SIII]_33.5{mu}m_, and [SiII]. More than 75% of these galaxies are classified as starburst-dominated sources in the mid-infrared, based on the [NeV]/[NeII] line flux ratios and equivalent width of the 6.2{mu}m polycyclic aromatic hydrocarbon feature.

We compare ratios of the emission-line fluxes to those predicted from stellar photo-ionization and shock-ionization models to constrain the physical and chemical properties of the gas in the starburst LIRG nuclei. Comparing the [SIV]/[NeII] and [NeIII]/[NeII] line ratios to the Starburst99-Mappings III models with an instantaneous burst history, the emission-line ratios suggest that the nuclear starbursts in our LIRGs have ages of 1-4.5 Myr, metallicities of 1-2Z_{sun}_, and ionization parameters of 2-8x10^7^cm/s.