The origin of the [C II] emission in the S140 PDRs - new insights from HIFI

TL;DR

This study uses Herschel's HIFI instrument to analyze the origin of [C II] emission in S140 PDRs, revealing multiple emission regions and a hot gas component near IRS1, advancing understanding of photon-dominated regions.

Contribution

First high-resolution analysis of [C II] emission in S140 revealing multiple components and the hot gas contribution near IRS1.

Findings

Identified three distinct [C II] emission regions in S140.

Discovered a hot, small component near IRS1, likely from irradiated outflow walls.

HIFI's resolution uncovered an additional hot gas component not seen before.

Abstract

Using Herschel's HIFI instrument we have observed [C II] along a cut through S140 and high-J transitions of CO and HCO+ at two positions on the cut, corresponding to the externally irradiated ionization front and the embedded massive star forming core IRS1. The HIFI data were combined with available ground-based observations and modeled using the KOSMA-tau model for photon dominated regions. Here we derive the physical conditions in S140 and in particular the origin of [C II] emission around IRS1. We identify three distinct regions of [C II] emission from the cut, one close to the embedded source IRS1, one associated with the ionization front and one further into the cloud. The line emission can be understood in terms of a clumpy model of photon-dominated regions. At the position of IRS1, we identify at least two distinct components contributing to the [C II] emission, one of them a small, hot component, which can possibly be identified with the irradiated outflow walls. This is consistent with the fact that the [C II] peak at IRS1 coincides with shocked H2 emission at the edges of the outflow cavity. We note that previously available observations of IRS1 can be well reproduced by a single-component KOSMA-tau model. Thus it is HIFI's unprecedented spatial and spectral resolution, as well as its sensitivity which has allowed us to uncover an additional hot gas component in the S140 region.