The puzzling distribution of the high-density molecular gas in HH 1-2: A contracting interstellar toroid?

Publication date: 
Main author: 
Torrelles J.M.
IAA authors: 
Torrelles J.M.;Gómez J.F.
Torrelles J.M., Gómez J.F., Ho T.P.P., Rodríguez L.F., Anglada G., Cantó J.
Astrophysical Journal
Publication type: 
We have performed a mosaic analysis of the region containing the HH 1-2 system. We combined five fields of NH3(1, 1) and (2, 2) spectral line observations using the VLA in its D configuration. This mosaic analysis allowed us to recover ∼80% of the total NH3(1, 1) flux obtained with single-dish observations. The total mass of the molecular gas in the region is estimated to be ∼52 (XNH3/10-8)-1M⊙. We find two remarkable elongated structures of ∼0.4 pc (∼3′) in size, approximately parallel to each other, while oriented almost perpendicular to the HH 1-2 outflow and the magnetic field in the region. The major axes of these elongated structures are displaced ∼20″ northwest and ∼10″ southeast of VLA 1, respectively. There is a velocity difference of ∼2 km s-1 between the two structures, but there is no significant velocity gradient along the major axis of either structure. Molecular gas at intermediate velocities between the velocities of the two elongated structures is found at their northeastern and southwestern ends. The exciting source of the HH 1-2 outflow may be physically closer to the elongated molecular structure displaced to the southeast of VLA 1, since the gas temperature is higher there, TK ≃ 18 K. The kinematical and spatial distribution of the elongated structures with respect to the [S II] emission of the HH 1-2 system, the blueshifted motions of HH 1 with respect to HH 2, the ambient velocities observed at the ends of the elongated structures, and finally the velocity gradient observed along the minor axis of the southeastern elongated structure, are consistent with a scenario where these two elongated structures represent the two halves of a contracting self-gravitating interstellar toroid seen almost edge-on, with the southeastern side in the foreground and redshifted with respect to the northwestern side. We favor a scenario where the star formation processes in the HH 1-2 region have produced at least two concentric flattened structures surrounding VLA 1, one with an interstellar size of ∼0.4 pc and the other one two orders of magnitude smaller ( ≲ 103 AU). This smaller structure, not evident in our data, is required to collimate the jet from VLA 1. Within this scenario, the HH 1-2 system would represent a case where the idea that inflow and outflow are taking place simultaneously in young stellar objects is supported.
ISM: individual (HH 1-2); ISM: jets and outflows; ISM: kinematics and dynamics; ISM: molecules; Stars: pre-main-sequence