Table \[tab-1\], 40%-60% of the very massive galaxies are characterized by ages consistent with the age of the universe at the targeted redshifts ($\sim1.6-2.1\times10^{9}$ yr). About 30% of the very massive galaxies, namely C1-6110, C1-15182, C1-22857, and C1-23152 have SFR estimates from SED modeling consistent with no star formation activity to within 1 $\sigma$, independent of the specific SED-modeling assumptions adopted in FAST. Of the remaining galaxies, 4 have very large SFRs, of the order of a few hundreds solar masses per year. We stress that the estimated ages and star formation rates from SED modeling are quite uncertain, even with the high-quality dataset used in this work (e.g., @muzzin09).

Rest-frame UV
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The rest-frame $U-V$ colors range from $U-V=1.01$, typical of nearby irregular galaxies, to $U-V=2.2$, typical of local elliptical galaxies (e.g., @fukugita95). The median $\langle U-V \rangle=1.64$ is similar to local Sb spiral galaxies. As shown in the middle panel of Figure \[fig-histos\], the mass-selected sample of @vandokkum06 at $z=2.5$, which is complete in stellar mass down to $\sim6\times10^{10}$ M$_{\sun}$ (a factor of $\sim5$ less than our sample), encompasses the range in $U-V$ colors spanned by our $z=3.5$ sample, with a median $U-V$ color bluer by $\sim0.1$ mag 