Evolution and Kinematics of Protostellar Envelopes in the Perseus Molecular Cloud

TL;DR

This study analyzes the evolution of protostellar envelopes in the Perseus molecular cloud, revealing how their shapes, orientations, and angular momentum change with protostellar age, and comparing these properties across different scales.

Contribution

It provides new insights into envelope evolution, especially the change in orientation relative to outflows and the scaling of angular momentum from large to small scales.

Findings

Envelope elongation becomes perpendicular to outflow with increasing Tbol.

Angular difference changes notably at Tbol ≈ 53 K, near the Class 0/I boundary.

Velocity gradient scales as R^{-0.72}, indicating how rotation varies with radius.

Abstract

We present a comprehensive analysis on the evolution of envelopes surrounding protostellar systems in the Perseus molecular cloud using data from the MASSES survey. We focus our attention to the C$^{18}$O(2--1) spectral line, and we characterize the shape, size, and orientation of 54 envelopes and measure their fluxes, velocity gradients, and line widths. To look for evolutionary trends, we compare these parameters to the bolometric temperature Tbol, a tracer of protostellar age. We find evidence that the angular difference between the elongation angle of the C$^{18}$O envelope and the outflow axis direction generally becomes increasingly perpendicular with increasing Tbol, suggesting the envelope evolution is directly affected by the outflow evolution. We show that this angular difference changes at Tbol = $53 \pm 20$ K, which includes the conventional delineation between Class 0 and I protostars of 70K. We compare the C$^{18}$O envelopes with larger gaseous structures in other molecular clouds and show that the velocity gradient increases with decreasing radius ($|\mathcal{G}| \sim R^{-0.72 \pm 0.06}$). From the velocity gradients we show that the specific angular momentum follows a power law fit $J/M \propto R^{1.83 \pm 0.05}$ for scales from 1pc down to $\sim$500 au, and we cannot rule out a possible flattening out at radii smaller than $\sim$1000 au.