Relationship between formation redshift ﹩{z}_{50}﹩ (the redshift by when 50% of the stellar mass had formed), the observed redshift z_grism, and Σ₁ (the stellar-mass surface density within 1 pkpc). (a) shows ﹩{z}_{50}﹩ as a function of ﹩\mathrm{log}({{\rm{\Sigma }}}_{1})﹩ for the quiescent galaxies in our sample. Galaxies with ﹩\mathrm{log}{{\rm{\Sigma }}}_{1}/({M}_{\odot }{\mathrm{kpc}}^{-2}))\gt 10﹩ (﹩\lt 10﹩) are shown as circles (diamonds). The color and size of the all points scales with increasing z_grism. Galaxies with ﹩\mathrm{log}{{\rm{\Sigma }}}_{1}/({M}_{\odot }{\mathrm{kpc}}^{-2})\lt 10﹩ span a larger range of ﹩{z}_{50}﹩. Galaxies with log Σ₁ / (M_⊙ kpc⁻²) > 10 favor higher formation redshifts of ﹩{z}_{50}\gt 3﹩. (b) shows the change in ﹩{z}_{50}﹩ as a function of ﹩\mathrm{log}({{\rm{\Sigma }}}_{1})﹩ using the Locally Weighted Scatterplot Smoothing (LOWESS) algorithm with bootstrapping to estimate the 68% confidence region. (c) shows the scatter in ﹩{z}_{50}﹩ as a function of ﹩\mathrm{log}({{\rm{\Sigma }}}_{1})﹩ (using LOWESS). Galaxies with higher Σ₁ tend toward higher ﹩{z}_{50}﹩ with lower scatter. (d) shows the change in ﹩{z}_{50}﹩ as function of ﹩\mathrm{log}{({M}_{* }/{M}_{\odot })}_{\mathrm{grism}}﹩ using LOWESS. Higher mass galaxies tend toward higher ﹩{z}_{50}﹩, though this relation is less steep while there is a continued rise between ﹩{z}_{50}﹩ vs. the stellar-mass surface density, Σ₁. (e) shows the formation redshift, ﹩{z}_{50}﹩, against the observed redshift. Galaxies with ﹩\mathrm{log}({{\rm{\Sigma }}}_{1})﹩/ ﹩({M}_{\odot }\,{\mathrm{kpc}}^{-2})\gt 10﹩ (﹩\lt 10﹩) are indicated by red (purple) points, using the LOWESS algorithm to show the trend. We see here that more compact galaxies (i.e., with higher Σ₁) tend to have higher z₅₀, particularly for ﹩z\lesssim 1.25﹩.