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Astron. Astrophys. 342, 213-232 (1999)

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6. Summary

We compared selected fields from the [FORMULA] keV ROSAT all-sky survey against the Leiden/Dwingeloo H I survey looking for correlations between HVCs and soft X-ray emission. We considered the soft X-ray radiation transfer in detail towards several prominent HVC complexes. Our results show that:

  1. The observed SXRB shows a smooth diffuse X-ray source intensity distribution at the higher latitudes (see Fig. 7).

  2. Small- and large-scale [FORMULA] variations of the observed SXRB distribution can be attributed to photoelectric absorption.

  3. H I alone traces the amount of soft X-ray absorbing interstellar matter well.

  4. Warm H I (i.e. the intercloud medium) traces most of the soft X-ray absorbing interstellar medium.

  5. The intensity of the distant X-ray emission decreases with increasing angular distance to the galactic center, implying that most of the distant soft X-ray emission is galactic in origin. The distant SXRB shows comparable intensities on the northern and southern sky.

  6. The distant soft X-ray emission probably consists of a superposition of a galactic X-ray plasma component [FORMULA] and a component of unresolved extragalactic point sources. More than 50% of the total radiation observed towards the galactic anticenter can be attributed to the galactic halo plasma emission.

The above results are consistent with those of Pietz et al. (1998a; 1998b).

We detected the following deviations from the smooth distant galactic X-ray background intensity distribution towards several prominent HVC complexes:

  1. Large portions of HVC complex C are positionally associated with excess soft X-ray emission.

  2. Towards a part of HVC complex D, we detected enhanced soft X-ray emission, positionally associated with an HVC filament. However, we note that there is also an IVC close to this area of excess emission.

  3. We detected enhanced soft X-ray emission in the direction of Mrk 509, where Sembach et al. (1995) found highly-ionized gas associated with HVC complex GCN.

  4. Towards complex WA we found inconclusive evidence for excess X-rays.

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© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998