"Probing the central power sources of ULIRG nuclei using Spitzer-IRS"

Ultraluminous Infrared Galaxies (ULIRGs) have the power output of quasars yet emit nearly all of their energy in the mid and far-infrared part of the spectrum. Most ULIRGs are found in interacting and merging systems, where the merger has driven gas and dust towards the remnant nucleus, fueling a massive starburst, and either creating or fueling a nascent AGN. The study of dusty (U)LIRG nuclei has greatly benefitted from the availability of the IRS spectrograph on the Spitzer Space Telescope. Given its unprecedented sensitivity and wavelength coverage, the IRS enabled us to use traditional mid-infrared starburst and AGN tracers such as [Ne II], [Ne III] and [Ne V] to investigate the balance between AGN and starburst in these systems. In addition, IRS observations of emission and absorption features of various gas phase molecules (e.g. CO, C2H2, HCN), water ice, hydrocarbons (both aromatic and aliphatic) and (crystalline) silicates allows us to gain insight in the nature and distribution of the obscuring gas and dust and the energy sources buried among them.