FUSE Observations of the Loop I/Local Bubble Interaction Region

TL;DR

This study used FUSE satellite data to measure OVI emission across the Loop I and Local Bubble interaction zone, revealing the spatial distribution and likely origins of the observed ultraviolet emission.

Contribution

It provides new measurements of OVI emission in the interaction zone, distinguishing local from distant contributions and suggesting emission arises mainly at interfaces.

Findings

Most OVI emission is from the distant side of the zone.

OVI emission within Loop I likely originates at interfaces.

CIII emission is similar on both sides, indicating near-side origin.

Abstract

We used the FUSE (Far Ultraviolet Spectroscopic Explorer) satellite to observe OVI emission along two sightlines towards the edge of the interaction zone (IZ) between the Loop I superbubble and the Local Bubble. One sightline was chosen because material in the interaction zone blocks distant X-ray emission, and should thus do the same for non-local OVI emission. We measured an OVI intensity of I_shadowed = 2750 +- 550 L.U. along this `Shadowed' sightline, and I_unshadowed = 10800 +- 1200 L.U. along the other sightline. Given these results, very little (< 800 L.U.) of the emission arises from the near side of the interaction zone, which likely has an HI column density of about 4e+20 cm-2 along the `Shadowed' sightline. The OVI emission arising within Loop I (~1e+4 L.U.) is probably associated with gas of n_e ~ 0.1 cm-3 and an emitting pathlength of ~1.2 pc, suggesting it arises at interfaces rather than from gas filling Loop I. In contrast, the CIII emission is similar along both sightlines, indicating that much of the emission likely arises on the near side of the interaction zone.