A spider-like outflow in Barnard 5 - IRS 1: The transition from a collimated jet to a wide-angle outflow?

Abstract

We present line and continuum observations made with the Submillimeter Array (SMA) of the young stellar object Barnard 5 - IRS1 located in the Perseus molecular cloud. Our $^{12}$CO(2-1) line observations resolve the high-velocity bipolar northeast-southwest outflow associated with this source. We find that the outflowing gas shows different structures at three different velocity regimes, in both lobes, resulting in a spider-like morphology. In addition to the low-velocity, cone-like (wide-angle) lobes that have previously been observed, we report the presence of intermediate-velocity parabolic shells emerging very close to the Class I protostar, as well as high velocity molecular bullets that appear to be associated to the optical/IR jet emanating from this source. These compact high-velocity features reach radial velocities of about 50 km s$^{-1}$ away from the cloud velocity. We interpret the peculiar spider-like morphology is a result of the molecular material being entrained by a wind with both a collimated jet-like component and a wide-angle component. We suggest the outflow is in a transitional evolutionary phase between a mostly jet-driven flow and an outflow in which the entrainment is dominated by the wide-angle wind component. We also detect 1300 $\mu$m continuum emission at the position of the protostar, which likely arises from the dusty envelope and disk surrounding the protostar. Finally, we report the detection of $^{13}$CO(2-1) and SO(6$_5$-5$_4$) emission arising from the outflow and the location of the young stellar object.