Morphological Complexity of Protostellar Envelopes

TL;DR

This paper investigates the complex, irregular structures of protostellar envelopes observed in infrared extinction maps, suggesting non-equilibrium collapse and potential implications for binary star formation.

Contribution

It provides detailed observations of envelope morphologies and links their complexity to initial core conditions and asymmetric infall processes.

Findings

Many envelopes show non-axisymmetric, filamentary structures.

Complex envelope morphology is often independent of outflow cavities.

Kinematic evidence indicates asymmetric infall in at least one case.

Abstract

Extinction maps at 8 micron from the Spitzer Space Telescope show that many Class 0 protostars exhibit complex, irregular, and on-axisymmetric structure within the densest regions of their dusty envelopes. Many of the systems have highly irregular and on-axisymmetric morphologies on scales $\sim$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. We suggest that the observed envelope complexity is 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 then show that the kinematics around L1165 as probed with N2H+ are indicative of asymmetric infall; the velocity gradient is not perpendicular to the outflow.