Novel methods of measuring star formation burstiness

Galaxies' star formation is tightly coupled with the myriad internal and external physical processes that affect their cool gas. In particular, measurements of star formation burstiness (short timescale stochasticity) are important for understanding how galaxies assemble their stellar populations over time as well as the feedback mechanisms that regulate star formation on ≲ 100 Myr timescales. We define a burst state indicator η = log₁₀(SFRʜα/SFRɴᴜᴠ) that compares a galaxy's star formation rate over the past ∼ 10 Myr and ∼ 100 Myr. Because η indicates whether a galaxy's star formation rate is rising, falling, or constant, the width of the η distribution for an ensemble of galaxies can be used to infer star formation burstiness. We first measure burstiness for observed 3D-HST galaxies and compare against mock catalogs created from Santa Cruz Semi-Analytic Models and MUFASA hydrodynamical simulations designed to replicate measurement uncertainties and selection effects for 3D-HST and upcoming JWST surveys. This analysis finds an unexpected trend between η and M⁎ in observations that was not present in the mocks, but which can be partially resolved by assuming that dust has a similar magnitude of effect on nebular emission lines and stellar light. To better understand how dust affects measurements of η, we extend our initial analysis by adding MOSDEF spectroscopy allowing for independent dust corrections for nebular and stellar light, as well as FMOS-COSMOS spectroscopy to expand our sample. Using a similar mock catalog approach, we find decent agreement between the mock catalogs and their respective surveys; however, the FMOS-COSMOS and MOSDEF mocks show a systematically lower median and scatter in η in comparison to observations. This work also presents the novel approach of analytically deriving the relationship between the intrinsic scatter in η, scatter added by measurement uncertainties, and observed scatter, resulting in an intrinsic burstiness measurement for galaxies at z ∼ 1 of 0.06 – 0.16 dex.Ph.D.Includes bibliographical reference