Introduction

Since the discovery of bipolar molecular outflows, a significant observational effort has been made to study the role of the dense molecular cores (n(H2) ≤ 104 cm−3) in the collimation processes. Dense molecular gas is almost always found in association with the central regions of a bipolar outflow. As a matter of fact, there is practically a one-to-one correspondence. This association of dense gas with the central parts of bipolar outflows supports the notion that the energy source of the outflows is a very young star (Torrelles et al. 1986a). There is also evidence that molecular toroids or discs with interstellar dimensions are present in several regions and that they play, at least on the scale of tenths of pc, an important role in the collimation and channelling of the high-velocity gas. See Rodríguez (1988) and Snell (this volume) for reviews.

In the last few years, our group has obtained Very Large Array (VLA) NH3 observations toward regions of molecular outflows. These observations have revealed the morphology of the high-density molecular gas on scales of ∼ 3″. This program allowed: (1) the study of dense gas as a possible focusing mechanism of bipolar outflows, (2) the study of local heating effects produced by star formation, and (3) the analysis of the kinematics of the regions. Here we present VLA NH3(1,1) and NH3(2,2) observations toward four regions with molecular outflows. These observations were obtained with the VLA of the National Radio Astronomy Observatory (NRAO)5.