Velocity-resolved [Fe II] line spectroscopy of L1551 IRS 5: A partially ionized wind under collimation around an ionized fast jet

We present a new [Fe II] lambda1.644 mum emission-line image of the L1551 IRS 5 jets and a velocity-resolved spectrum obtained with the Subaru Telescope. In the [Fe II] line image showing two separate jetlike features, a strong and spatially wide [Fe II] emission feature was found elongated along the northern jet at its base. The echelle spectrum taken along this feature shows two prominent velocity components together with underlying pedestal and wing emissions. The entire emission range is blueshifted with respect to the systemic velocity, which shows that the emission originates from an outflow. The high-velocity component (HVC) at V-LSR = -300 km s(-1), which has a corresponding Halpha emission, consistently shows a narrow line width of similar to40 km s(-1) (deconvolved FWHM value). The low-velocity component (LVC) at V-LSR = 100 km s(-1), on the other hand, has no corresponding Halpha feature and is located spatially closer to the IRS 5 VLA sources (IRS 5 VLA) than is the HVC. The LVC shows broad line widths of 130-160 km s(-1) (FWHM) near IRS 5 VLA, while its line width decreases with increasing distance from it. We interpret from these characteristics that the HVC is a spatially narrow, well-collimated ionized stellar jet and that the LVC is a widely opened, partially ionized disk wind that is being collimated as it travels away from the origin. The inclination-corrected velocity of the HVC, 440 km s(-1), may imply that the accreting protostar driving the jet is rotating at almost its breakup speed. The LVC has an inclination-corrected wind velocity of similar to200 km s(-1), suggesting that it is accelerated at the region where the accretion disk is interacting with the stellar magnetic field. The pedestal and red wing features may represent the LVC gas entrained and accelerated by the HVC. It is possible that the two apparently parallel jetlike features seen more than 6" away from the IRS 5 VLA sources are the brightened edges of the partially ionized wind.