An Older, More Quiescent Universe from Panchromatic SED Fitting of the
  3D-HST Survey
  Galaxy observations are influenced by many physical parameters: stellar
masses, star formation rates (SFRs), star formation histories (SFHs),
metallicities, dust, black hole activity, and more. As a result, inferring
accurate physical parameters requires high-dimensional models which capture or
marginalize over this complexity. Here we re-assess inferences of galaxy
stellar masses and SFRs using the 14-parameter physical model
Prospector-$\alpha$ built in the Prospector Bayesian inference framework. We
fit the photometry of 58,461 galaxies from the 3D-HST catalogs at $0.5 < z <
2.5$. The resulting stellar masses are $\sim0.1-0.3$ dex larger than the
fiducial masses while remaining consistent with dynamical constraints. This
change is primarily due to the systematically older SFHs inferred with
Prospector. The SFRs are $\sim0.1-1+$ dex lower than UV+IR SFRs, with the
largest offsets caused by emission from "old" ($t>100$ Myr) stars. These new
inferences lower the observed cosmic star formation rate density by $\sim0.2$
dex and increase the observed stellar mass growth by $\sim 0.1$ dex, finally
bringing these two quantities into agreement and implying an older, more
quiescent Universe than found by previous studies at these redshifts. We
corroborate these results by showing that the Prospector-$\alpha$ SFHs are both
more physically realistic and are much better predictors of the evolution of
the stellar mass function. Finally, we highlight examples of observational data
which can break degeneracies in the current model; these observations can be
incorporated into priors in future models to produce new & more accurate
physical parameters.
