Author(s): , , , ,
Institution(s): 1. Arizona State University, 2. CEA/Saclay, 3. SSC/Caltech, 4. Universidad Diego Portales, 5. University of Virginia
Luminous and Ultra-luminous Infrared Galaxies ((U)LIRGs) represent the most important galaxy population at redshifts z > 1 as they account for more than 50% of all star formation produced in the Universe at those epochs; and encompass what it is called the main-sequence (MS) of star-forming galaxies. Investigating their local counterparts –low luminosity LIRGs– is therefore key to understand the physical properties and phases of their inter-stellar medium (ISM) – a task that is rather challenging in the distant Universe. On the other hand, high-z star-bursting (out of the MS) systems, although small in number, account for a modest yet still significant fraction of the total energy production. Here I present far-IR line emission observations ([CII]158μm, [OI]63μm, [OIII]88μm and [NII]122μm) obtained with Herschel for two large samples of nearby LIRGs: The Great Observatories All-sky LIRG Survey (GOALS), a sample of more than 240 relatively cold LIRGs, and a survey of 30 LIRGs selected to have very warm mid- to far-IR colors, suggestive of an ongoing intense nuclear starburst and/or an AGN. Using photo-dissociation region (PDR) models we derive the basic characteristics of the ISM (ionization intensity and density) for both samples and study differences among systems as a function of AGN activity, merger stage, dust temperature, and compactness of the starburst – parameters that are thought to control the life cycle of galaxies moving in and out of the MS, locally and at high-z.