Observations of Shocked H[TINF]2[/TINF] and Entrained CO in Outflows from Luminous Young Stars

Abstract

Narrowband, H2 (1–0) S(1) images of six luminous outflow regions are presented and discussed. In five of these regions, W75 N, S140 N, NGC 7538, AFGL 5180, and AFGL 490, H2 shock features associated with molecular (CO) outflows are observed. We have discovered faint, though extensive, bow shocks in the W75 N outflow that indicate a total flow length of at least 3 pc. The Herbig-Haro knots that make up the HH 251–254 outflow in S140 N are also observed in H2; in addition, knots in the counterflow are discovered. Copious H2 emission is also observed throughout the NGC 7538 region; filamentary structures to the northeast of the central cluster (IRS 1) are probably photodissociation fronts, although a jetlike structure is observed associated with the IRS 9 CO outflow. In AFGL 5180, a new, collimated H2 jet is discovered to the east of the central cluster, and numerous knots and filaments are observed around the cluster itself that could be associated with the known CO outflow there. Last, H2 line emission is observed southwest of AFGL 490; in particular, a bright peak is found associated with a warm molecular clump in the CO outflow. To complement these data, wide-field CO J = 2–1 maps have also been obtained toward three regions, W75 N, S140 N, and NGC 7538. When compared with the H2 images, these provide new insight into each outflow region. Indeed, analysis of these data suggests that although these flows are more massive and more energetic than their low-mass counterparts, they are nevertheless well collimated, bipolar, and possibly jet-driven. Molecular bow shocks, driven by an underlying, possibly variable stellar jet, may play a major role in this entrainment process.