Gaia and Chandra Detangle Multiple Young Stellar Populations in the Direction of NGC 6357

We present a sample of ~ 800 young stellar objects (YSOs) in the field of the NGC 6357 massive star-forming complex detected with the Chandra X-ray Observatory observations and appearing in Gaia EDR3. We also cross-matched our list with near- and mid-IR Galactic plane survey catalogs produced by VVV/2MASS, and GLIMPSE. The unprecedented astrometric precision of Gaia EDR3 (0.4 mas/yr) reveals 70% of these stars are grouped into three proper motion clusters identified visually and confirmed using DBScan. The largest proper motion cluster contains 722 sources including Pismis 24 and the two more obscured massive stellar clusters in NGC 6357. Two distinct, smaller proper motion clusters (57 sources) differ from the main cluster by Δμ_RA ~ 2 mas/yr and Δμ_Dec ~ 0.1 mas/yr. The parallax distribution of the main cluster peaks at ~ 0.5 mas while the two smaller proper motion clusters peak at ~ 1 mas. While one of the smaller proper motion clusters is scattered spatially across the field, the other is concentrated in the northwestern region of NGC 6357. We combine our sample with a larger set of YSOs from the SPICY catalog, including those without X-ray detection, for a combined membership list of ~1000 YSOs in NGC 6357.