Galaxies 09: Assembly, Gas Content and Star Formation History of Galaxies

DongChan Kim
University of Virginia

Mid-IR Diagnostics of Star Formation in QUEST Sample

The Quasar/ULIRGs Evolution Study (QUEST) is a comprehensive program designed to study the evolutionary connection between ultraluminous infrared galaxies (ULIRGs) and quasar hosts. This program combines optical and near-infrared imaging and spectroscopic data obtained from the ground and from the space with the Hubble Space Telescope (H-band imaging) and Spitzer Space Telescope (IRS spectroscopy). Here, we report a summary of mid-IR diagnostics of star formation in 74 ULIRGs and 34 Palomar Green (PG) quasars. Six independent methods have been applied to quantify starburst fraction to the bolometric luminosity in these systems. On average, a starburst contribution in ULIRGs is $\sim$60\%, ranging from $\sim$75\% among cool ($f_{25}/f_{60} <$~0.2) optically classified HII-like and LINER ULIRGs to $\sim$50\% and $\sim$25\% among warm Seyfert 2 and Seyfert 1 ULIRGs, respectively. This number decreases $\sim$20\% in PG QSOs. We find a morphological trend along the strong, modest, and weak starburst-dominated ULIRGs to the PG QSO sequence, in general agreement with the standard ULIRG to QSO evolutionary scenario.

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