Theoretical Astrophysics Seminars

27th Seminar (Part 3)


The Evolution of Star-Forming Galaxies Over Cosmic Time

Josh Speagle

Harvard University, Kavli IPMU


The assembly and evolution of galaxies over cosmic time is a complex process. Historically, galaxy evolution was thought to be governed by mainlystochastic, potentially divergent processes such as major mergers, whichwere linked to active galactic nuclei (AGN) activity and vigorous starformation followed by a rapid "quenching" process. In the last decade or so, however, observations have shown that there exists a strong correlation (~.25 dex) between star formation rates (SFRs) and stellar masses (M) among star-forming galaxies (SFGs) at a wide range of redshifts covering the majority of the age of the Universe. Dubbed the "main sequence" (MS), the existence of this tight M-SFR relationship hints that galaxy formation and evolution might in fact be a deterministic process rather than a stochastic one. Using new first epoch SPLASH data as well as other results from the literature, we investigate the effective evolution of the MS over the majority of the age of the universe (out to z~6, t~.9 Gyr), finding a remarkable consensus among all the available data and deriving a robust functional form for the MS as afunction of time. The results are compared to SDSS quasar data, where a remarkable similar evolution is observed. We use these results to propose possible joint AGN-galaxy evolution models. Other interesting features of the MS relation that have previously only been noted, such as a supposed turnoff at high masses, are also discussed.