A Spitzer Study of Interacting Luminous and Ultra-Luminous Infrared
  Galaxies
  We conducted a Spitzer Space Telescope survey of 28 Luminous (11 <
log(LIR/L_odot) < 12, LIRGs) and Ultra-Luminous Infrared Galaxies
(log(LIR/L_odot) > 12, ULIRGs). Many of these galaxies are found in pairs or
associations and are powered by either nuclear activity or starformation
(Sanders & Mirabel 1996). Our main goal is to understand the relative
importance of starbursts and AGNs in interacting systems. Is the frequency of
AGN and starbursts in these interacting galaxies related to their luminosities?
What is the importance of the merger stage and the frequency of AGNs? We
present our conclusions and diagnostic diagrams based in the observed near
infrared lines and compare to studies based solely in optical data.
