Searching for Planets Orbiting Fomalhaut with JWST

We report observations obtained with the JWST/NIRCam coronagraph of the Fomalhaut (α PsA) system. This nearby, young A star hosts a complex debris disk system first discovered by the IRAS satellite (Aumann 1985; Gillett 1986) and an object previously thought to be a planetary mass companion, Fomalhaut b, which recent observations have shown to be the remnants of a planetesimal collisional event. Observations in F444W and F356W filters using the round 430R mask achieve a contrast ratio of ∼ 4 × 10−7 at 1′′ and ∼ 4 × 10−8 outside of 3′′. These observations reach a sensitivity limit <1 MJup across most of the disk region, limited beyond ∼1′′−2′′ by detector noise and integration time, not residual starlight. Numerous sources seen in earlier coronagraphic imaging with the Keck telescope or the Hubble Space Tele- scope (HST) are recovered with NIRCam and shown to be background objects. Consistent with the hypothesis that Fomalhaut b is not a massive planet, we do not detect it in either F356W or F444W where a Jovian-sized planet should be bright. We have reliably detected five sources and two fainter ones in and around Fomalhaut and its debris disk, all but one of which are coincident with Keck or HST sources. One object, S1, is coincident within the astrometric uncertainties with the so-called Great Dust Cloud (GDC) seen in MIRI imaging (Gaspar et al. 2023). But this object is spatially coincident with a Keck and Alma source making it a background object whose 3.56-25.5 μm spectral energy distribution resembles that of an infrared luminous galaxy like Arp 220 or M82 at a redshift of z ∼1. One of the faintest objects, S7, is located at the edge of the inner dust disk seen in the MIRI images, has no obvious counterpart in imaging at earlier epochs and has a relatively red [F356W]- [F444W]>0.7 mag (Vega) color. Whether this object is a background galaxy or brown dwarf, or a Jovian mass planet in the Fomalhaut system will be determined by an approved Cycle 2 follow-up program. Finally, we set upper limits to any scattered light from the outer ring, placing a weak limit on the dust albedo at F356W and F444W.