A detailed temperature map of the archetypal protostellar shocks in L1157

TL;DR

This study uses ammonia line imaging to map temperature and chemical variations in protostellar shocks in L1157, revealing shock heating and chemical enhancements at high spatial resolution.

Contribution

It provides the first detailed temperature and chemical maps of protostellar shocks in L1157 using multiple ammonia lines at high resolution.

Findings

Ammonia ortho-to-para ratio is enhanced along the jet path.

Temperature gradient from >120 K to <80 K across shock regions.

Column density of ammonia is significantly increased in shock cavities.

Abstract

We present sensitive $\rm NH_3$ (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 $\rm NH_3$ 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 $\rm 10\,km\,s^{-1}$; it also shows a strong spatial correlation with the $\rm NH_3$ column density, which is enhanced to $\rm >10^{16}\,cm^{-2}$ toward the shock cavities. At a linear resolution of 1500 au, our refined temperature map from the seven $\rm NH_3$ lines shows a gradient from the warm B0 eastern cavity wall ($\rm >120\,K$) to the cool cavity B1 and the earlier shock B2 ($\rm <80\,K$), indicating shock heating.