Molecular Gas and the Evolutionary Connection Between Submillimeter Galaxies and AGN at z~2-3

Mon, September 21, 2015

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Theoretical work has suggested that active galactic nuclei (AGN) play an important role in quenching star formation in massive galaxies. Direct evidence for AGN affecting the molecular ISM (the gas phase that fuels star formation) has so far been limited to detections of molecular outflows in low-redshift systems and extreme excitation regions which represent a tiny fraction of the total gas. Indirect evidence for AGN's impact on their host galaxies' star-forming cold gas may be provided by measurements of the gas excitation and dynamics. At z~2-3, the peak epoch of star formation and AGN activity, previous observations of the CO(1-0) line revealed that submillimeter galaxies (SMGs) have multi-phase molecular gas, including substantial reservoirs of cold-phase gas. However, the entirety of the molecular gas in AGN-host galaxies appears highly excited. This dichotomy provides tantalizing support an evolutionary connection between these two populations. I will present a new VLA sample that nearly doubles the number of CO(1-0) detections in z~2-3 SMGs and AGN-host galaxies that allows us to better compare the cold gas properties of these systems and further investigate evidence for the effects of AGN on the star-forming molecular gas. This work complements our nearly completed molecular gas blank field surveys which will indirectly probe the mechanisms that shut off star formation by measuring the CO luminosity function and its evolution with cosmic time.