A Detailed Study of Spitzer-IRAC Emission in Herbig-Haro Objects (II): Interaction Between Ejecta and Ambient Gas

Abstract

We present a new analysis of the physical conditions in three Herbig-Haro complexes (HH 54, HH 212, and the L 1157 protostellar jet) using archival data from the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. As described in detail in Paper I, the emission observed using the 4.5-micron filter is enhanced in molecular shocks (T=1000-4000 K) at relatively high temperature or densities compared with that observed with the 8.0-micron filter. Using these data sets, we investigate different distributions of gas between high and low temperatures/densities. Our analysis reveals the presence of a number of warm/dense knots, most of which appear to be associated with working surfaces such as the head of bow shocks and cometary features, and reverse shocks in the ejecta. These are distributed not only along the jet axis, as expected, but also across it. While some knotty or fragmenting structures can be explained by instabilities in shocked flows, others can be more simply explained by the scenario that the mass ejection source acts as a "shot gun", periodically ejecting bullets of material along similar but not identical trajectories. Such an explanation challenges to some degree the present paradigm for jet flows associated with low-mass protostars. It also give clues to reconciling our understanding of the mass ejection mechanism in high and low mass protostars and evolved stars.

36 pages, 14 figures, 3 tables, accepted by Astrophysical Journal

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Cited by in corpus (11)

• Molecular jets from low-mass young protostellar objects
• First image of the L1157 molecular jet by the CALYPSO IRAM-PdBI survey
• The CHESS survey of the L1157-B1 bow-shock: high and low excitation water vapor
• Origin of Misalignments: Protostellar Jet, Outflow, Circumstellar Disc, and Magnetic Field
• Rotating Bullets from A Variable Protostar
• Emission Mechanism of "Green Fuzzies" in High-mass Star Forming Regions
• The L1157 protostellar outflow imaged with the SMA
• Probing jets from young embedded sources: clues from HST near-IR [Fe II] images
• YSO jets in the Galactic Plane from UWISH2: V - Jets and Outflows in M17
• Spitzer-IRAC survey of molecular jets in Vela-D
• Imaging of HH80-81 jet in the NIR shock tracers H${}_2$ and [Fe II]