ALMA and Keck analysis of Fomalhaut field sources: JWST's Great Dust Cloud is a background object

TL;DR

This study uses ALMA and Keck data to show that several compact sources near Fomalhaut, including the 'Great Dust Cloud,' are background objects, demonstrating the importance of multi-epoch, multi-wavelength observations in confirming exoplanet candidates.

Contribution

It provides a method to distinguish background objects from true companions in JWST exoplanet imaging by combining ground-based and space-based observations over time.

Findings

Multiple sources coincide with JWST detections but are background objects.

Ground-based data from 6 to 18 years prior rule out common proper motion.

Multi-wavelength data helps validate exoplanet candidates.

Abstract

At 7.7 pc, the A-type star Fomalhaut hosts a bright debris disk with multiple radial components. The disk is eccentric and misaligned, strongly suggesting that it is sculpted by interaction with one or more planets. Compact sources are now being detected with JWST, suggesting that new planet detections may be imminent. However, to confirm such sources as companions, common proper motion with the star must be established, as with unprecedented sensitivity comes a high probability that planet candidates are actually background objects. Here, ALMA and Keck observations of Fomalhaut are found to show significant emission at the same sky location as multiple compact sources in JWST MIRI coronagraphic observations, one of which has been dubbed the "Great Dust Cloud" because it lies within the outer belt. Since the ground-based data were obtained between 6 to 18 years prior to the JWST observations, these compact sources are unlikely to be common proper motion companions to Fomalhaut. More generally, this work illustrates that images collected at a range of wavelengths can be valuable for rejecting planet candidates uncovered via direct imaging with JWST.