Probing the Protostellar Envelope Around L1157: The Dust and Gas Connection

We present observations of the Class 0 protostar L1157-mm using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in 3 mm dust continuum and N 2 H + line emission. In the N 2 H + line, we detect a large-scale envelope extended over a linear size of ∼20,000 AU flattened in the direction perpendicular to the outflow. This N 2 H + feature coincides with the outer envelope seen in the 8 μm extinction by Looney et al. Meanwhile, the dust continuum traces the compact, nearly spherical structure of the inner envelope, where N 2 H + becomes depleted. This highly flattened N 2 H + envelope also shows dynamical signatures consistent with gravitational infall in the inner region, but a slow, solid-body rotation at large scales. This flattened structure is not a rotationally supported circumstellar disk; instead, it resembles a prestellar core both morphologically and kinematically, representing the early phase of a Class 0 system. In this paper, we construct a simple model to interpret both the dust continuum and N 2 H + emission and suggest a possible dynamical scenario for the overall properties of the envelope.