background caused by foreground HI clouds have been detected mainly in soft X-rays by Egger & Aschenbach (1995). However, the feature detected in the ROSAT maps by Böhringer (1994) is seen in the hard energy band (0.4–2.4 keV), and is thus difficult to attribute it to gas absorption.

EUVE observations of the Virgo cluster (VC) center (Lieu 1996) show the presence of gas at $\sim$0.5 10$^6$ K near M87. This matter forms an additional component of the intra-cluster material (ICM) in Virgo, as follows from their analysis, and cannot be the same hot gas which is responsible for the X-ray emission detected by ROSAT. In order to confirm the existence of this second ICM component of the VC, Lieu (1996) performed HI 21 cm observations with the 43-m Green Bank telescope (angular resolution 21’). The region surveyed by them was centered on M87, had an extent of 2$^{\circ}\times1^{\circ}.6$, and the grid of HI measurements was spaced every 8’$\simeq$1/3 of a resolution element.

A comparison of the HI map of Lieu (1996) with the FIR distributions (see Figure 1) demonstrates that the FIR emission follows the total HI column density. Although Lieu do not mention the velocity range over which the 