title: Episodic molecular outflow in the very young protostellar cluster Serpens South.
abstract: The loss of mass from protostars, in the form of a jet or outflow, is a necessary counterpart to protostellar mass accretion. Outflow ejection events probably vary in their velocity and/or in the rate of mass loss. Such 'episodic' ejection events have been observed during the class 0 protostellar phase (the early accretion stage), and continue during the subsequent class I phase that marks the first one million years of star formation. Previously observed episodic-ejection sources were relatively isolated; however, the most common sites of star formation are clusters. Outflows link protostars with their environment and provide a viable source of the turbulence that is necessary for regulating star formation in clusters, but it is not known how an accretion-driven jet or outflow in a clustered environment manifests itself in its earliest stage. This early stage is important in establishing the initial conditions for momentum and energy transfer to the environment as the protostar and cluster evolve. Here we report that an outflow from a young, class 0 protostar, at the hub of the very active and filamentary Serpens South protostellar cluster, shows unambiguous episodic events. The (12)C(16)O (J = 2-1) emission from the protostar reveals 22 distinct features of outflow ejecta, the most recent having the highest velocity. The outflow forms bipolar lobes--one of the first detectable signs of star formation--which originate from the peak of 1-mm continuum emission. Emission from the surrounding C(18)O envelope shows kinematics consistent with rotation and an infall of material onto the protostar. The data suggest that episodic, accretion-driven outflow begins in the earliest phase of protostellar evolution, and that the outflow remains intact in a very clustered environment, probably providing efficient momentum transfer for driving turbulence.
authors.affiliation: Astronomy Department, Yale University, New Haven, Connecticut 06511, USA.
authors.forename: Adele L
authors.initials: AL
authors.lastname: Plunkett
authors.affiliation: Astronomy Department, Yale University, New Haven, Connecticut 06511, USA.
authors.forename: Héctor G
authors.initials: HG
authors.lastname: Arce
authors.affiliation: Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile.
authors.forename: Diego
authors.initials: D
authors.lastname: Mardones
authors.affiliation: Astronomy Department, Yale University, New Haven, Connecticut 06511, USA.
authors.forename: Pieter
authors.initials: P
authors.lastname: van Dokkum
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, Massachusetts 02138, USA.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Dunham
authors.affiliation: Instituto Argentino de Radioastronomía, CCT-La Plata (CONICET), C.C.5, 1894, Villa Elisa, Argentina.
authors.forename: Manuel
authors.initials: M
authors.lastname: Fernández-López
authors.affiliation: Joint ALMA Observatory, Av. Alonso de Córdova 3107, Vitacura, Santiago, Chile.
authors.forename: José
authors.initials: J
authors.lastname: Gallardo
authors.affiliation: Joint ALMA Observatory, Av. Alonso de Córdova 3107, Vitacura, Santiago, Chile.
authors.forename: Stuartt A
authors.initials: SA
authors.lastname: Corder