Quasar Metal Abundances & Host Galaxy Evolution

Quasars signal a unique phase of galaxy evolution – when massive spheroids are rapidly being assembled, forming stars and growing their central super-massive black holes. Measurements of the metal abundances around quasars provide unique information about these complex evolutionary processes. Here we provide a brief review of the current status and implications of quasar abundance research. The central goal of quasar abundance studies is to understand the evolutionary relationship between quasars, super-massive black holes (SMBHs) and their host galaxies. We know that a close relationship exists because dormant SMBHs are not only common in galactic nuclei today, but their masses, M BH , scale directly with the mass of the surrounding galactic spheroids, M gal , (e.g., Tremaine et al. 2002). Whatever processes created the galactic spheroids must have also (somehow) created central SMBHs with commensurate mass. Luminous quasars represent the final major growth stage(s) of the most massive SMBHs inside the most massive galaxies. The quasar phase is very brief, of order 10 8 yr, but it coincides with a critical stage of SMBH–galaxy evolution when galactic spheroids are still rapidly being assembled and making stars. The energy output from accreting black holes might, in fact, regulate that star formation and thus lead naturally to the observed M BH – M gal correlation (Kauffmann & Haehnelt 2000, Granato et al. 2004). Quasar abundance studies can help us understand better the complex evolutionary relationship between SMBHs and their host galaxies. For example, how much star formation (how much conversion of the initial gas into stars) occurs in galactic spheroids before the visible quasar epoch? Did the major star-forming episodes occur before, during or after the final luminous stages of SMBH growth? Is the relative timing of these events consistent with quasars triggering star formation, shutting it down, or having no affect at all? How much do outflows during the quasar epoch contribute to the distribution of metals to the 1