JWST/NIRCam Imaging of Young Stellar Objects. I. Constraints on Planets Exterior to the Spiral Disk Around MWC 758

MWC 758 is a young star hosting a spiral protoplanetary disk. The spirals are likely companion-driven, and two previously identified candidate companions have been identified—one at the end the Southern spiral arm at ∼0.″6, and one interior to the gap at ∼0.″1. With JWST/NIRCam, we provide new images of the disk and constraints on planets exterior to ∼1″. We detect the two-armed spiral disk, a known background star, and a spatially resolved background galaxy, but no clear companions. The candidates that have been reported are at separations that are not probed by our data with sensitivity sufficient to detect them‑nevertheless, these observations place new limits on companions down to ∼2 M _Jup at ∼150 au and ∼0.5 M _Jup at ≳600 au. Owing to the unprecedented sensitivity of JWST and youth of the target, these are among the deepest mass-detection limits yet obtained through direct imaging observations, and provide new insights into the system's dynamical nature.