A possible trail of dust from a young, highly-extincted brown dwarf in the outskirts of the Trapezium Cluster

ABSTRACT

We present the JWST discovery of a highly extincted ($A_V\sim 52$) candidate brown dwarf (${\sim} 0.018$ M$_\odot$) in the outskirts of the Trapezium Cluster that appears to be coincident with the end of a ${\sim} 1700$ au long, remarkably uniformly wide, dark trail that broadens only slightly at the end opposite the point source. We examine whether a dusty trail associated with a highly extincted brown dwarf could plausibly be detected with JWST and explore possible origins. We show that a dusty trail associated with the brown dwarf could be observable if dust within it is larger than that in the ambient molecular cloud. For example, if the ambient cloud has a standard ${\sim} 0.25$ $\mu$m maximum grain size and the trail contains micron-sized grains, then the trail will have a scattering opacity over an order of magnitude larger compared to the surroundings in NIRCam short-wavelength filters. We use a simple model to show that a change in maximum grain size can reproduce the high $A_V$ and the multifilter NIRCam contrast seen between the trail and its surroundings. We propose and explore two possible mechanisms that could be responsible for the trail: (i) a weak far ultraviolet radiation-driven wind from the circum-brown dwarf disc due to the O stars in the region and (ii) a Bondi–Hoyle–Lyttleton accretion wake. The former would be the most distant known case of the Trapezium stars’ radiation driving winds from a disc, and the latter would be the first known example of ‘late’ infall from the interstellar medium on to a low-mass object in a high-mass star-forming region.