Protostellar Evolution in Serpens Main: Possible Origin of Disk-size Diversity

We have observed the submillimeter continuum condensations SMM2, SMM4, SMM9, and SMM11 in the star-forming cluster Serpens Main using the Atacama Large Millimeter/submillimeter Array during Cycle 3 in the 1.3 mm continuum, ¹²CO J = 2 - 1, SO J _N = 6₅ - 5₄, and C¹⁸O J = 2 - 1 lines at an angular resolution of ∼0.″55 (240 au). Sixteen sources have been detected in the 1.3 mm continuum, which can be classified into three groups. Group 1 consists of six sources showing extended continuum emission and bipolar/monopolar ¹²CO outflows. Although all the Group 1 members are classified as Class 0 protostars, our observations suggest evolutionary trends among them in terms of ¹²CO outflow dynamical time, SO emission distribution, C¹⁸O fractional abundance, and continuum morphology. Group 2 consists of four sources associated with a continuum filamentary structure and no ¹²CO outflows. Central densities estimated from the 1.3 mm continuum intensity suggest that they are prestellar sources in a marginally Jeans unstable state. Group 3 consists of six Spitzer sources showing point-like 1.3 mm continuum emission and clumpy ¹²CO outflows. These features of Group 3 suggest envelope dissipation, preventing disk growth from the present size, r ≲ 60 au. The Group 3 members are protostars that may be precursors to the T Tauri stars associated with small disks at radii, of tens of astronomical units, identified in recent surveys.