Evolution and Kinematics of Protostellar Envelopes in the Perseus
  Molecular Cloud
  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.
