Spitzer observations of the HH 1/2 system: The discovery of the counterjet

Abstract

We present unpublished Spitzer IRAC observations of the HH 1/2 young stellar outflow processed with a high angular resolution deconvolution algorithm that produces subarcsecond (∼0″.6-0″.8) images. In the resulting mid-infrared images, the optically invisible counterjet is detected for the first time. The counterjet is approximately half as bright as the jet at 4.5μm (the IRAC band that best traces young stellar outflows) and has a length of ∼10″. The NW optical jet itself can be followed back in the mid-IR to the position of the exciting VLA 1 source. An analysis of the IRAC colors indicates that the jet/counterjet emission is dominated by collisionally excited H2 pure rotational lines arising from a medium with a neutral hydrogen gas density of ∼1000-2000cm-3 and a temperature of ∼1500 K. The observed jet/counterjet brightness asymmetry is consistent with an intrinsically symmetric outflow with extinction from a dense, circumstellar structure of ∼6″ size (along the outflow axis), and with a mean visual extinction, AV ∼ 11 mag. © 2012. The American Astronomical Society. All rights reserved.