A Detailed Temperature Map of the Archetypal Protostellar Shocks in L1157

We present sensitive NH3 (1,1)-(7,7) line images from the Karl G. Jansky Very Large Array toward successive shocks, which are associated with the blueshifted outflow lobe driven by the compact protobinary system L1157. Within a projection distance of 0.1 pc, our observations not only trace the quiescent and cold gas in the flattened envelope, but also illustrate the complex physical and chemical processes that take place where the high-velocity jet impinges on its surrounding medium. Specifically, the NH3 ortho-to-para ratio is enhanced by a factor of 2-2.5 along the jet path, where the velocity offset between the line peak and the blueshifted wing reaches values as high as 10 km s(-1); it also shows a strong spatial correlation with the NH3 column density, which is enhanced to >10(16) cm(-2) toward the shock cavities. At a linear resolution of 1500 au, our refined temperature map from the seven NH3 lines shows a gradient from the warm B0 eastern cavity wall (>120 K) to the cool cavity B1 and the earlier shock B2 (<80 K), indicating shock heating.

Automated summary

Sensitive NH3 (1,1)-(7,7) line images from the Karl G. Jansky Very Large Array reveal successive shocks and complex physical and chemical processes in the blueshifted outflow lobe driven by the protobinary system L1157. The ortho-to-para ratio of NH3 is enhanced along the jet path, with a strong spatial correlation between NH3 column density and shock cavities. A refined temperature map shows a gradient from warm to cool regions, indicating shock heating.