Evolution and Kinematics of Protostellar Envelopes in the Perseus Molecular Cloud

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 T bol , 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 T bol , suggesting the envelope evolution is directly affected by the outflow evolution. We show that this angular difference changes at T bol = 53 ± 20 K, which includes the conventional delineation between Class 0 and I protostars of 70 K. 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 (|G| ∼ R −0.72±0.06 ). From the velocity gradients we show that the specific angular momentum follows a power law fit J/M ∝ R 1.83±0.05 for scales from 1pc down to ∼500 au, and we cannot rule out a possible flattening out at radii smaller than ∼1000 au.

The role of magnetic fields in the formation of protostars, disks, and outflows

“…Gaudel et al (2020) finds a break in the angular momentum evolution with radius, from a steep profile j ∝ r 1.6 at radii r > 1600 au, to a quasi-flat profile at radii 50-1600 au. These profiles are shown in the right panel of Figure 2, together with the SMA MASSES measurements from Heimsoth et al (2021) in the left panel.…”

“…Molecular line observations are also used to characterize the angular momentum contained in the star-forming gas, ultimately responsible for the formation of the protostellar disks. Recent observations of Class 0 protostellar envelopes at large scales (>1000 au) suggest the specific angular momentum scales with envelope radii, following a power-law relation j ∝ r 1.8 between 1000 and 10000 au, with values ranging from 10 −5 to a few 10 −3 km s −1 pc at 1000 au (Yen et al 2015b;Pineda et al 2019;Heimsoth et al 2021). In the CALYPSO survey, molecular line observations at sub-arcsecond resolution have allowed characterization of protostellar gas motions down to ∼ 50 au scales.…”