A search for soft X-ray emission associated with prominent high-velocity-cloud complexes

We correlate the ROSAT 1/4 keV all-sky survey with the Leiden/Dwingeloo HI survey, looking for soft X-ray sig natures of prominent high-velocity-cloud (HVC) complexes. We study the transfer 1/4 keV photons through the interst ellar medium in order to distinguish variations in the soft X-ray data are modelled as a combination of emission from the Local Hot Bubble (LHB) and e mission from a distant plasma in the galactic halo and extragalactic source s. The X-ray radiation intensity of the galactic halo and extragalactic X-r ay background is modulated by the photoelectric absorption of the interveni ng galactic interstellar matter. We show that large- and small-scale intens ity variations of the 1/4 keV SXRB are caused by photoelectric absorption w hich is predominantly traced by the total N-HI distribution. The extensive coverage of the two surveys supports evidence for a hot, X-ray emitting cor ona. We show that this leads to a good representation of the SXRB observati ons. For four large areas on the sky, we search for regions where the model led and observed X-ray emission differ. We find that there is excess X-ray emission towards regions near HVC complexes C, D, and GCN. We suggest that the excess X-ray emission is positionally correlated with the high-velocity clouds. Some lines of sight towards HVCs also pass through significant amo unts of intermediate-velocity gas, so we cannot constrain the possible role played by IVC gas in these directions of HVC and IVC overlap, in determini ng the X-ray excesses.