The Spatial Distribution of Star Formation in the Solar Neighbourhood: Do all stars form in clusters?

TL;DR

This study analyzes the distribution of young stellar objects in nearby star-forming regions, finding a smooth lognormal distribution with no evidence for distinct modes of star formation, and that only a small fraction of stars form in dense clusters.

Contribution

It provides a comprehensive analysis of YSO surface densities in the solar neighbourhood, challenging the idea of multiple star formation modes and quantifying the fraction of stars in dense environments.

Findings

YSO surface densities follow a lognormal distribution.

No evidence for multiple discrete star formation modes.

Less than 26% of stars form in dense environments.

Abstract

We present a global study of low mass, young stellar object (YSO) surface densities in nearby (< 500 pc) star forming regions based on a comprehensive collection of Spitzer Space Telescope surveys. We show that the distribution of YSO surface densities in the solar neighbourhood is a smooth distribution, being adequately described by a lognormal function from a few to 10^3 YSOs per pc^2, with a peak at 22 stars/pc^2 and a dispersion of 0.85. We do not find evidence for multiple discrete modes of star-formation (e.g. clustered and distributed). Comparing the observed surface density distribution to previously reported surface density threshold definitions of clusters, we find that the fraction of stars in clusters is crucially dependent on the adopted definitions, ranging from 40 to 90%. However, we find that only a low fraction (< 26%) of stars are formed in dense environments where their formation/evolution (along with their circumstellar disks and/or planets) may be affected by the close proximity of their low-mass neighbours.