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Abstract We present a comprehensive analysis of 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 ( ∣  ∣ ∼ 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 1 pc down to ∼500 au, and we cannot rule out a possible flattening out at radii smaller than ∼1000 au. 

ABSTRACT We present ALMA 3 mm molecular line and continuum observations with a resolution of ∼3.5 arcsec towards five first hydrostatic core (FHSC) candidates (L1451-mm, Per-bolo 58, Per-bolo 45, L1448-IRS2E, and Cha-MMS1). Our goal is to characterize their envelopes and identify the most promising sources that could be bona fide FHSCs. We identify two candidates that are consistent with an extremely young evolutionary state (L1451-mm and Cha-MMS1), with L1451-mm being the most promising FHSC candidate. Although our envelope observations cannot rule out Cha-MMS1 as an FHSC yet, the properties of its CO outflow and SED published in recent studies are in better agreement with the predictions for a young protostar. For the remaining three sources, our observations favour a pre-stellar nature for Per-bolo 45 and rule out the rest as FHSC candidates. Per-bolo 58 is fully consistent with being a Class 0, while L1448 IRS2E shows no emission of high-density tracers (NH2D and N2H+) at the location of the previously identified compact continuum source, which is also undetected in our observations. Thus, we argue that there is no embedded source at the presumptive location of the FHSC candidate L1448 IRS2E. We propose instead that what was thought to be emission from the presumed L1448 IRS2E outflow corresponds to outflow emission from a nearby Class 0 system, deflected by the dense ambient material. We compare the properties of the FHSC candidates studied in this work and the literature, which shows that L1451-mm appears as possibly the youngest source with a confirmed outflow.