A Large Diversity in the Quiescent Fractions of Massive Galaxies in Proto-clusters at $z\sim4-6$ in the FRESCO GOODS fields

To constrain the emergence of the first quiescent galaxies (QGs) and their connection to large-scale structure, we search for rare, high-redshift QGs in proto-clusters using spectral energy distribution modeling, multiple rest-frame color diagnostics, and visual inspection. Our sample includes 12 QG candidates with stellar masses log(M*/Msun) ~ 9-11 in four proto-clusters at z ~ 4-6 within GOODS-North (GOODS-N) and GOODS-South (GOODS-S). The selection uses 11 NIRCam filters in GOODS-N and 17 NIRCam plus 2 MIRI filters in GOODS-S, combined with 9 ancillary HST filters, covering 0.4-7.7 microns. We measure an increasing quiescent fraction with stellar mass, with averages of 1.0%(+0.7/-0.4; 5/502), 3.5%(+2.8/-1.7; 4/115), and 33.3%(+22.2/-17.5; 3/9) for log(M*/Msun) = 9 - 9.75, 9.75 - 10.5, 10.5 - 11.25, respectively, across four proto-clusters. Notably, the two GOODS-N proto-clusters at z=4.406 and z=5.194 have a quiescent fraction of 100% (2/2 at z=4.406; 1/1 at z=5.194) in their highest mass bin (log(M*/Msun) > 10.5), whereas the proto-clusters in GOODS-S at similar redshifts have zero massive quiescent galaxies. Contrary to the expectation that massive galaxies occupy cluster centers at z~0, our QGs are found primarily on the outskirts of overdensity peaks. We also find fewer robust QGs at z>5 (1/8) and none in the z=5.384 proto-cluster, consistent with simulations suggesting that efficient quenching mechanisms had not yet matured. Our results highlight the pronounced variations in quiescent fractions across proto-clusters at z>4. The emerging diversity of proto-cluster QG populations calls for a stronger understanding of the role of environment in early galaxy evolution.