Asca Observations Of Luminous Infrared Galaxies

One of the most important results of the IRAS survey is the discovery of a class of “Luminous Infrared Galaxies” (LIGs), which emit most of the energy in the infrared and are the dominant population in the local universe at luminosities above 1011 L☉ (e.g., Sanders & Mirabel 1996). All LIGs appear to be extremely rich in molecular gas, and many of them show evidence of recent interacting/merging activities. Hence it is now accepted that strong interactions of gas-rich galaxies triggers large central concentration of molecular gas, and makes optimal conditions for both enormous nuclear starbursts and building and/or fueling AGN. Actually, various observations show evidence of starburst activity as well as that of AGN in many LIGs (Sanders & Mirabel 1996).