Beyond UVJ: Color Selection of Galaxies in the JWST Era

We present a new rest-frame color-color selection method using synthetic u ( s ) - g ( s ) and g ( s ) - i ( s ), (ugi)( s ) colors to identify star-forming and quiescent galaxies. Our method is similar to the widely used U - V versus V - J (UVJ) diagram. However, UVJ suffers known systematics. Spectroscopic campaigns have shown that UVJ-selected quiescent samples at z & GSIM; 3 include & SIM;10%-30% contamination from galaxies with dust-obscured star formation and strong emission lines. Moreover, at z > 3, UVJ colors are extrapolated because the rest-frame band shifts beyond the coverage of the deepest bandpasses at mu m (typically Spitzer/IRAC 4.5 mu m or future JWST/NIRCam observations). We demonstrate that (ugi)( s ) offers improvements to UVJ at z > 3, and can be applied to galaxies in the JWST era. We apply (ugi)( s ) selection to galaxies at 0.5 < z < 6 from the (observed) 3D-HST and UltraVISTA catalogs, and to the (simulated) JAGUAR catalogs. We show that extrapolation can affect (V - J)(0) color by up to 1 mag, but changes (gs-is)0 s -selected quiescent samples are comparable to UVJ in completeness (both achieve & SIM;85%-90% at z = 3-3.5), (ugi)( s ) reduces contamination in quiescent samples by nearly a factor of 2, from ? 35% to ? 17% at z = 3, and from & SIME;60% to & SIME;33% at z = 6. This leads to improvements in the true-to-false-positive ratio (TP/FP), where we find TP/FP ? 2.2 for (ugi)( s ) at z & SIME; 3.5 - 6, compared to TP/FP < 1 for UVJ-selected samples. This indicates that contaminants will outnumber true quiescent galaxies in UVJ at these redshifts, while (ugi)( s ) will provide higher-fidelity samples.