HH 223: a parsec-scale H 2 outflow in the star-forming region L723 (original) (raw)
2010, Astronomy & Astrophysics
Context. The dark cloud Lynds 723 (L723) is a low-mass star-forming region where one of the few known cases of a quadrupolar CO outflow has been reported. Two recent works have found that the radio continuum source VLA 2, towards the centre of the CO outflow, is actually a multiple system of young stellar objects (YSOs). Several line-emission nebulae that lie projected on the eastwest CO outflow were detected in narrow-band Hα and [S ii] images. The spectra of the knots are characteristic of shock-excited gas (Herbig-Haro spectra), with supersonic blueshifted velocities, which suggests an optical outflow also powered by the VLA 2 YSO system of L723. Aims. Our aim is to study L723 in the near-infrared and look for line-emission nebulae associated with the optical and CO outflows. Methods. We imaged a field of ∼ 5 × 5 centred on HH 223, which includes the whole region of the quadrupolar CO outflow with narrow-band filters centred on the [Fe ii] 1.644 µm and H 2 2.122 µm lines, together with off-line H c and K c filters. The [Fe ii] and H 2 line-emission structures were identified after extracting the continuum contribution, if any. Their positions were determined from an accurate astrometry of the images. Results. The H 2 line-emission structures appear distributed over a region of 5. 5 (∼ 0.5 pc for a distance of 300 pc) at both sides of the VLA 2 YSO system, with an S-shape morphology, and are projected onto the east-west CO outflow. Most of them were resolved in smaller knotty substructures. The [Fe ii] emission only appears associated with HH 223. An additional nebular emission from the continuum in H c and K c appears associated with HH 223-K1, the structure closest to the VLA 2 YSO system, and could be tracing the cavity walls. Conclusions. We propose that the H 2 structures form part of a large-scale near-infrared outflow, which is also associated with the VLA 2 YSO system. The current data do not allow us to discern which of the YSOs of VLA 2 is powering this large scale optical/nearinfrared outflow.
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