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We present a detailed analysis of Spitzer-IRAC images obtained toward sixHerbig-Haro objects (HH 54/211/212, L 1157/1448, BHR 71). Our analysisincludes: (1) comparisons in morphology between the four IRAC bands (3.6, 4.5,5.8 and 8.0 um), and H2 1-0 S(1) at 2.12 um for three out of six objects; (2)measurements of spectral energy distributions (SEDs) at selected positions; and(3) comparisons of these results with calculations of thermal H2 emission atLTE (207 lines in four bands) and non-LTE (32-45 lines, depending on particlefor collisions). We show that the morphologies observed at 3.6 and 4.5 um aresimilar to each other, and to H2 1-0 S(1). This is well explained by thermal H2emission at non-LTE if the dissociation rate is significantly larger than0.002-0.02, allowing thermal collisions to be dominated by atomic hydrogen. Incontrast, the 5.8 and 8.0 um emission shows different morphologies from theothers in some regions. This emission appears to be more enhanced at the wakesin bow shocks, or less enhanced in patchy structures in the jet. Thesetendencies are explained by the fact that thermal H2 emission in the 5.8 and8.0 um band is enhanced in regions at lower densities and temperatures.Throughout, the observed similarities and differences in morphology betweenfour bands and 1-0 S(1) are well explained by thermal H2 emission. The observedSEDs are categorized into:- (A) those in which the flux monotonically increaseswith wavelength; and (B) those with excess emission at 4.5-um. The type-A SEDsare explained by thermal H2 emission, in particular with simple shock modelswith a power-law cooling function. Our calculations suggest that the type-BSEDs require extra contaminating emission in the 4.5-um band. The COvibrational emission is the most promising candidate, and the othercontaminants discussed to date are not likely to explain the observed SEDs.

A Detailed Study of Spitzer-IRAC Emission in Herbig-Haro Objects (I): Morphology and Flux Ratios of Shocked Emission