Disentangling Star Formation and Active Galactic Nuclei Activity over Cosmic Time (Alexandra Pope, University of Massachusetts)

Luminous infrared galaxies are known to play a significant role in massive galaxy evolution as they dominate the star formation rate density during the peak period from z=1-3. Spitzer mid-infrared spectroscopy has revealed that some high redshift luminous infrared galaxies have much stronger polycyclic aromatic hydrocarbon (PAH) emission and, correspondingly, weaker active galactic nuclei (AGN) activity than in their local counterparts hinting at an evolution with redshift. To test these results we have assembled a library of ~150 mid-IR spectra of IR luminous galaxies at z>1 in fields with the deepest images in the X-ray, optical, mid-IR, far-IR (Herschel), submm and radio. Together these data allow us to decompose the bolometric luminosity into contributions from star formation and AGN, and investigate the variation in these processes as a function of redshift, luminosity and galaxy type. An understanding of the distribution and variation of dust emission in high redshift galaxies can help to determine how intense star formation proceeds in the obscured galaxies that are orchestrating massive galaxy formation through major mergers or turbulent gas-rich disks.