A non-uniform distribution of the nearest brown dwarfs

TL;DR

This study reveals a non-uniform distribution of nearby brown dwarfs compared to stars, suggesting potential observational biases and implications for understanding substellar populations and Galactic dynamics.

Contribution

It provides the first assessment of the spatial distribution of the nearest brown dwarfs on the Galactic plane, highlighting a significant non-uniformity.

Findings

Brown dwarfs are unevenly distributed, with more behind the Sun.

Stars show a uniform distribution, unlike brown dwarfs.

The observed distribution may be influenced by observational biases.

Abstract

The census of solar neighbours is still complemented by new discoveries, mainly of very low-mass, faint dwarfs, close to or within the substellar domain. These discoveries contribute to a better understanding of the field population; its origin in terms of Galactic dynamics and (sub)stellar formation and evolution. Also, the nearest stars and brown dwarfs at any given age allow the most precise direct characterization, including the search for planetary companions. We aim to further assess the substellar census on the Galactic plane. We projected the 136 stars and 26 brown dwarfs known at <6.5 pc on the Galactic plane and evaluated their distributions. Stars present a uniform- and brown dwarfs a non-uniform distribution, with 21 objects behind the Sun and only five ahead relative to the direction of rotation of the Galaxy. This substellar configuration has a probability of 0.098$^{+10.878}_{-0.098}$% relative to uniformity. The helio- and geocentric nature of the distribution suggests it might result in part from an observational bias, which if compensated for by future discoveries, might increase the brown-dwarf-to-star ratio, shifting it closer to values found in some star forming regions.