Improved Measurements of Galaxy Star Formation Stochasticity from the Intrinsic Scatter of Burst Indicators

Measurements of short-timescale star formation variations (i.e., "burstiness") are integral to our understanding of star formation feedback mechanisms and the assembly of stellar populations in galaxies. We expand upon the work of Broussard et al. (2019) by introducing a new analysis of galaxy star formation burstiness that accounts for variations in the $Q_{sg}=\mathrm{E(B-V)_{stars}}/\mathrm{E(B-V)_{gas}}$ distribution, a major confounding factor. We use Balmer decrements from the MOSFIRE Deep Evolution Field (MOSDEF) survey to measure $Q_{sg}$, which we use to construct mock catalogs from the Santa Cruz Semi-Analytic Models and Mufasa cosmological hydrodynamical simulation based on 3D-HST, Fiber Multi-Object Spectrograph (FMOS)-COSMOS, and MOSDEF galaxies with H$\alpha$ detections. The results of the mock catalogs are compared against observations using the burst indicator $\eta = \log_{10}(\mathrm{SFR_{H\alpha}/SFR_{NUV}})$, with the standard deviation of the $\eta$ distribution indicating burstiness. We find decent agreement between mock and observed $\eta$ distribution shapes; however, the FMOS-COSMOS and MOSDEF mocks show a systematically low median and scatter in $\eta$ in comparison to the observations. This work also presents the novel approach of analytically deriving the relationship between the intrinsic scatter in $\eta$, scatter added by measurement uncertainties, and observed scatter, resulting in an intrinsic burstiness measurement of $0.06-0.16$ dex.