Shocked water in the Cep E protostellar outflow

TL;DR

This study detects high-velocity water emission in the Cep E protostellar outflow, revealing warm, dense gas with enhanced water abundance in shocks close to the protostar, using IRAM 30m and Plateau de Bure observations.

Contribution

First detection of water emission from high-velocity shocks in the Cep E outflow with detailed physical conditions derived.

Findings

Water emission originates from warm, dense gas near the protostar.

Water abundance is significantly enhanced in shock regions.

Water emission is similar in profile and distribution to SiO in the outflow.

Abstract

Previous far-infrared observations at low-angular resolution have reported the presence of water associated with low-velocity outflow shocks and protostellar envelopes. The outflow driven by the intermediate-mass class 0 protostar Cep E is among the most luminous outflows detected so far. Using the IRAM 30m telescope, we searched for and detected the para-water line emission at 183 GHz in the Cep E star-forming core. The emission arises from high-velocity gas close to the protostar, which is unresolved in the main beam of the telescope. Complementary observations at 2" resolution with the Plateau de Bure interferometer helped establish the origin of the emission detected and the physical conditions in the emitting gas. The water line profile and its spatial distribution are very similar to those of SiO. We find that the water emission arises from warm ($\sim 200\K$), dense ($(1-2)\times 10^6\cmmt$) gas, and its abundance is enhanced by one to two orders of magnitude with respect to the protostellar envelope. We detect water emission in strong shocks from the high-velocity jet at 1000 AU from the protostar. Despite the large beam size of the telescope, such emission should be detectable with Herschel.