On the spatial distributions of dense cores in Orion B

TL;DR

This study analyzes the spatial distribution and mass segregation of dense cores in Orion B, revealing significant substructure and primordial mass segregation likely influenced by magnetic fields, challenging competitive accretion models.

Contribution

It provides the first detailed quantification of core spatial distributions and mass segregation in Orion B, highlighting the role of magnetic fields over dynamical processes.

Findings

All three regions are spatially substructured.

Most massive cores are highly mass segregated in some regions.

Mass segregation is likely primordial, not dynamical.

Abstract

We quantify the spatial distributions of dense cores in three spatially distinct areas of the Orion B star-forming region. For L1622, NGC2068/NGC2071 and NGC2023/NGC2024 we measure the amount of spatial substructure using the $\mathcal{Q}$-parameter and find all three regions to be spatially substructured ($\mathcal{Q} < 0.8$). We quantify the amount of mass segregation using $\Lambda_{\rm MSR}$ and find that the most massive cores are mildly mass segregated in NGC2068/NGC2071 ($\Lambda_{\rm MSR} \sim 2$), and very mass segregated in NGC2023/NGC2024 ($\Lambda_{\rm MSR} = 28^{+13}_{-10}$ for the four most massive cores). Whereas the most massive cores in L1622 are not in areas of relatively high surface density, or deeper gravitational potentials, the massive cores in NGC2068/NGC2071 and NGC2023/NGC2024 are significantly so. Given the low density (10 cores pc$^{-2}$) and spatial substructure of cores in Orion B, the mass segregation cannot be dynamical. Our results are also inconsistent with simulations in which the most massive stars form via competitive accretion, and instead hint that magnetic fields may be important in influencing the primordial spatial distributions of gas and stars in star-forming regions.