Near-infrared echelle spectroscopy of Class I protostars: molecular hydrogen emission-line (MHEL) regions revealed

Infrared echelle spectra are used to trace dynamic activity in the immediate vicinity of Class I outflow sources. The H 2 and Brγ observations presented here trace different components of these emission-line regions; indeed, they are thought to trace the orthogonal processes of outflow and infall respectively. High-velocity H 2 emission is detected in the extended lobes of nine outflows. In addition, complex H 2 line emission is observed within a few hundred au of nine of the outflow sources. We refer to these H 2 emission regions as ‘molecular hydrogen emission-line’ regions, or MHELs, and compare their properties to those of forbidden emission-line regions (FELs) observed in classical T Tauri and some Herbig AeBe stars. Like the FELs, both low- and high-velocity components (LVCs and HVCs) are observed in H 2, with blueshifted velocities of the order of 5–20 and 50–150 km s−1 respectively. LVCs are more common than HVCs in MHEL regions, and like their FEL counterparts, the latter are spatially further offset from the exciting source in each case. The MHEL regions — which are in all cases preferentially blueshifted — are assumed to be associated with the base of each outflow. Brγ profiles are detected towards four of the Class I sources observed (SVS 13, IRAS 04239+2436, HH 34-IRS and GGD 27(1)) as well as towards the T Tauri star AS 353A. These lines are all broad and symmetric, the line peaks being blueshifted by ∼30 km s−1. The profiles are typical of the permitted hydrogen line profiles observed in many T Tauri stars, and probably derive from magnetospheric accretion flows. We do not observe redshifted absorption features (inverse P-Cygni profiles) in any of the sources, however. Nor do we detect a dependence on linewidth with inclination angle of the system to the line of sight, as is predicted by such accretion models. No Brγ is detected in the extended flow lobes. Instead, the emission is confined to the source and is spatially unresolved along each flow axis.