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

TL;DR

This paper reports the discovery of a highly-extincted brown dwarf with a dust trail in the Trapezium Cluster, exploring its possible origins and implications for dust properties and star formation processes.

Contribution

It presents the first detection of a dust trail associated with a brown dwarf in a high-mass star-forming region and models its possible formation mechanisms.

Findings

Dust trail could be detected if dust grains are larger than ambient cloud.

A simple model reproduces observed extinction and contrast with larger grains.

Two mechanisms proposed: FUV wind from circum-brown dwarf disc and accretion wake.

Abstract

We present the JWST discovery of a highly-extincted ($A_V\sim52$) candidate brown dwarf ($\sim0.018$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 $\sim0.25$$\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 multi-filter 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 FUV 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 onto a low mass object in a high-mass star-forming region.