Evidence for a very low-column density hole in the Galactic halo in the direction of the high latitude molecular cloud MBM 16

TL;DR

This study used Suzaku shadow observations towards MBM 16 to determine the presence of galactic halo emission, finding it negligible or absent within current measurement limits.

Contribution

The paper provides the first direct upper limits on galactic halo emission in the direction of MBM 16 using shadow observations, constraining halo models.

Findings

Galactic halo emission in the direction of MBM 16 is negligible or absent.

Upper limits on halo emission measure are at the low end of current estimates.

Foreground emissions from LHB and SWCX fully account for observed X-ray emission.

Abstract

Shadow observations are the only way to observe emission from the galactic halo (GH) and/or the circumgalactic medium (CGM) free of any foreground contamination from local hot bubble (LHB) and solar wind charge exchange (SWCX). We analyzed data from a shadow observation in the direction of the high latitude, neutral hydrogen cloud MBM 16 with \Suzaku. We found that all emission can be accounted for by foreground emission from LHB and SWCX, plus power law emission associated with unresolved point sources. The GH/CGM in the direction of MBM 16 is negligible or inexistent in our observation, with upper limits on the emission measure of 9.5x10^{-4} pc cm^{-6} (90% C.L.), at the lowest end of current estimates.