HH 223: a parsec-scale H₂ outflow in the star-forming region L723^⋆,⋆⋆

¹ Departament d’Astronomia i Meteorologia (IEEC-UB), Institut de Cièncias del Cosmos, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain
e-mail: rosario@am.ub.es; robert.estalella@am.ub.es
² Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
e-mail: jap@iac.es
³ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁴ GTC Office, Spain
e-mail: gabriel.gomez@gtc.iac.es
⁵ Instituto Astrofísica Andalucía, CSIC, Camino Bajo de Huétor 50, 18008 Granada, Spain
e-mail: gcharly@iaa.es

Received: 1 June 2010
Accepted: 2 August 2010

Abstract

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 east-west 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 H₂ 2.122 μm lines, together with off-line H_c and K_c filters. The [Fe ii] and H₂ 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 H₂ line-emission structures appear distributed over a region of ′̣ (~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 H₂ 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/near-infrared outflow.