Spatial structure in the soft x-ray diffuse background and the local interstellar medium

Data from five rocket flights of the Wisconsin soft x-ray sky survey covering the southern galactic hemisphere with moderate spatial resolution (60 FWHM) between 0.1 and 10 keV are analyzed. Burstein et.al (1977) and others have found that at intermediate and low galactic latitudes the observed pulse height distributions can not be fit with the emission from a single uniform-temperature plasma with or without absorption. This result is duplicated at higher latitudes. Maps of the spatial distribution of the x rays in various energy bands are presented. Brightness features within 400 of the galactic center that appear exclusively above E = 0.5 keV can be fit with thermal emission models involving plasma at T = 2 or 3 x 106K that may be associated with the radio continuum Loop I feature. The softer x rays (E < 0.3 keV) are apparently the emission from a fairly local plasma (d < 103 parsec) at T approx. = 106K that is closer to the sun than even the nearest 5 x 1019 cm-2 of neutral gas. Evidence is presented against the existence of nearby small (radius approx. = 0.6 parsec) clouds of cool neutral gas as has been recently proposed by McKee and Ostriker (1977). However, the spatial resolution and coverage of the present survey are not sufficient to rule out this possibility. The x-ray measurements are consistent with the small amounts of local neutral material inferred from Lyα absorption measurements