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 9.5 × 10 −4 pc cm −6 (90% C.L.), at the lowest end of current estimates. Subject headings: ISM: individual (local hot bubble) -Galaxy: halo -X-rays: diffuse background

A High Spectral Resolution Study of the Soft X-Ray Background with the X-Ray Quantum Calorimeter

“…lished that the thermal and spatial distribution of the halo is complex (e.g. Kuntz & Snowden 2000;Lei et al 2009;Yao et al 2009;Liu et al 2016), and a single temperature model is therefore likely overly simplistic. One should be careful not to ascribe too much significance to any physical interpretation.…”

The Structure of the Local Hot Bubble

“…DATA ANALYSIS Snowden et al (1998Snowden et al ( , 2000 used the shadows cast by nearby (100-200 pc) clouds to estimate and remove the contribution from background emission (Galactic halo and extragalactic components) to the RASS R1 and R2 maps, producing clean "local" maps (<100-200 pc). With the advance in X-ray telescopes, the shadow technique is now feasible for individual pointing for spectroscopy study to disentangle the foreground and background (Galeazzi et al 2007;Smith et al 2007;Gupta et al 2009;Henley et al 2015;Liu et al 2016;. These "local" maps should contain only the contribution from SWCX, both heliospheric (S( , b, t)) and geocoronal (G), and the LHB (L( , b)).…”