| Description |
We propose to survey CO spectral line energy distribution (SLED), from J=4-3 up to J=13-12, on 93 local luminous infrared galaxies (LIRGs; L_{IR} > 1.0E11 L_{sun}) with Herschel SPIRE FTS spectrometer. These galaxies, plus 32 additional LIRGs that will have similar data from existing Herschel programs (mainly the HerCULES project), form a flux-limited subset of the Great Observatories All-Sky LIRGs Survey (GOALS) sample. Our proposal is built on the legacy of GOALS and extends beyond the existing Herschel HerCULES program, which emphasizes more on ULIRGs, to a much needed sample coverage of the more numerous and diverse population of less luminous LIRGs. The data from the proposed observations will not only provide muchneeded local LIRG templates for future ALMA studies of high-redshiftcounterparts, but also lend us a powerful diagnostic tool to probe the warm and dense molecular gas that are more closely related to the starburst or AGN activity in the nuclei of LIRGs. The data from thisproposal will provide important statistical clues to the interplay between the cold and warm molecular gas, IR luminosity, star formationrate and efficiency, and the diverse properties of LIRGs. Specifically, using the homogeneous CO SLED data from this proposal, together with ground-base, low-order CO line data (mainly J=1-0) and other data that have been compiled for the GOALS sample, we will address the following questions: (1) What is the dominant nuclear power source in individual sample galaxy: starburst or AGN? (2) Whatare the typical physical properties of warm molecular gas in the nuclei of LIRGs? (3) How do the nuclear warm gas components correlate to the cold gas component, star formation rate and efficiency, dust temperature, etc? and (4) How does molecular gas excitation change along a merger sequence? |
