Radio Continuum–H2O Maser Systems in NGC 2071: H2O Masers Tracing a Jet (IRS 1) and a Rotating Proto–Planetary Disk of Radius 20 AU (IRS 3)

We have observed simultaneously the 1.3 cm continuum and H 2 O maser emission toward the core of the star-forming region NGC 2071 using the Very Large Array in its A configuration. Two 1.3 cm continuum sources have been detected in the region, coinciding with the infrared sources IRS 1 and IRS 3, respectively. The radio emission in IRS 3 is consistent with an ionized thermal bipolar radio jet. Two clusters of H 2 O maser spots are detected, one associated with IRS 1 (22 spots) and the other one associated with IRS 3 (13 spots). The H 2 O maser distribution in IRS 1 seems to be tracing at scales of 300 AU the larger scale H 2 outflow observed at a few thousands of AU from the exciting source. On the other hand, the H 2 O masers in IRS 3 are distributed as an apparent disk of ≃0 05 (≃20 AU) radius, oriented almost perpendicular to the major axis of the radio jet. There is a clear velocity gradient (≃0.35 km s -1 AU -1 ) along the major axis of the H 2 O maser distribution, which can be gravitationally bound by a central mass of ≃1 M ☉ . These results, together with the low-mass and early evolutionary stage of IRS 3, suggest that masers around this source are tracing a rotating proto-planetary disk within a proto-solar-like system. This represents direct kinematic evidence of the smallest rotating circumstellar disk ever observed around a young stellar object (YSO). We discuss the dichotomy of H 2 O masers tracing either outflows or disks around YSOs, based on the evolutionary scheme proposed in our earlier work. We suggested that systems in which H 2 O masers trace disks are less evolved than those in which masers trace outflows. In this scheme, IRS 3 would then represent a relatively less evolved object than IRS 1. This prediction is consistent with independent infrared observations showing that IRS 3 is at an earlier phase of evolution.