Are Starbursts the Progenitors of Supermassive Black Holes?

A popular model for the coevolution of bulges and supermassive black holes is one in which a galaxy merger leads to the inflow of gas which fuels a strong burst of star formation, followed by an AGN phase in which the black hole grows significantly. In this proposal we describe how mid-IR spectroscopy with Spitzer can directly test this model. Using the Sloan Digital Sky Survey to undertake a census of the growth of black holes in the local universe, we have found that a significant fraction of this growth seems to take place in a rare class of highly dust-obscured AGN hosted by morphologically disturbed galaxies whose optical spectra imply that they are in the post-starburst phase. Because of the high extinction in the optical, IRS data are required to: 1) Verify the presence of powerful AGN through measurements of the luminosity of the mid-IR [NeV] emission-lines, and 2) Verify that these are truly post-starbursts rather than dusty starbursts whose massive stars are invisible in the optical spectra. In this case, the discrimination will be primarily made using the equivalent widths of the PAH features. The combination of the robust statistics from the SDSS sample and the diagnostic power of the IRS will make this the best test to date of the significance of a starburst-to-AGN evolutionary pathway.