Complex Structure in Class 0 Protostellar Envelopes

TL;DR

This study reveals that many Class 0 protostars have complex, irregular envelope structures likely caused by initial non-equilibrium collapse, which may influence binary formation and is unrelated to outflow activity.

Contribution

It provides new high-resolution IRAC-based extinction maps showing complex, non-axisymmetric protostellar envelopes and links their morphology to initial core conditions and formation environments.

Findings

Many protostellar envelopes are irregular and non-axisymmetric.

Complex structures are often independent of outflow cavities.

Protostars tend to form near cloud edges or filament bends.

Abstract

We use archived IRAC images from the Spitzer Space Telescope to show that many Class 0 protostars exhibit complex, irregular, and non-axisymmetric structure within their dusty envelopes. Our 8 $\mu$m extinction maps probe some of the densest regions in these protostellar envelopes. Many of the systems are observed to have highly irregular and non-axisymmetric morphologies on scales >= 1000 AU, with a quarter of the sample exhibiting filamentary or flattened dense structures. Complex envelope structure is observed in regions spatially distinct from outflow cavities, and the densest structures often show no systematic alignment perpendicular to the cavities. These results indicate that mass ejection is not responsible for much of the irregular morphologies we detect; rather, we suggest that the observed envelope complexity is mostly the result of collapse from protostellar cores with initially non-equilibrium structures. The striking non-axisymmetry in many envelopes could provide favorable conditions for the formation of binary systems. We also note that protostars in the sample appear to be formed preferentially near the edges of clouds or bends in filaments, suggesting formation by gravitational focusing.