Unlocking the Keyhole - H2 and PAH emission from molecular clumps in the Keyhole Nebula

TL;DR

This study uses H2 and PAH emission imaging to analyze molecular clumps in the Keyhole Nebula, revealing their morphology, velocity structure, and the presence of photodissociation regions, shedding light on the nebula's environment.

Contribution

It provides the first detailed imaging of H2 and PAH emissions in the Keyhole Nebula, linking molecular clump velocities with their spatial and photodissociation region characteristics.

Findings

H2 and PAH emissions are morphologically similar and align with CO emission clumps.

Clumps at different velocities are positioned at various locations relative to the ionization region.

The clumps are likely remnants of the molecular cloud influenced by eta Car's stellar winds.

Abstract

To better understand the environment surrounding CO emission clumps in the Keyhole Nebula, we have made images of the region in H2 1-0 S(1) (2.122 um) emission and polycyclic aromatic hydrocarbon (PAH) emission at 3.29 um. Our results show that the H2 and PAH emission regions are morphologically similar, existing as several clumps, all of which correspond to CO emission clumps and dark optical features. The emission confirms the existence of photodissociation regions (PDRs) on the surface of the clumps. By comparing the velocity range of the CO emission with the optical appearance of the H2 and PAH emission, we present a model of the Keyhole Nebula in which the most negative velocity clumps are in front of the ionization region, the clumps at intermediate velocities are in it, and those which have the least negative velocities are at the far side. It may be that these clumps, which appear to have been swept up from molecular gas by the stellar winds from eta Car, are now being over-run by the ionization region and forming PDRs on their surfaces. These clumps comprise the last remnants of the ambient molecular cloud around eta Car.