EVIDENCE FOR A VERY LOW-COLUMN DENSITY HOLE IN THE GALACTIC HALO IN THE DIRECTION OF THE HIGH LATITUDE MOLECULAR CLOUD MBM 16

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 pc cm −6 (90% C.L.-solar metallicity), at the lowest end of current estimates.