Green Bank observations were performed, we assumed these to be at $\sim$0 km s$^{-1}$ because they are supposedly of “Galactic HI” origin. While some VC galaxies do have negative heliocentric velocities (c.f. Binggeli 1985), they mostly concentrate at 1,000–2,000 km s$^{-1}$. For this reason, we think it likely that the HI detected by Lieu (1996) does indeed belong to the MW and, by inference, so does the material producing the FIR emission. We note at this point that the center of the low N(HI) region, at 12:28+12:45 (1950) and only $\sim$half a degree away from M87, has N(HI)$\simeq$1.8 10$^{20}$ atoms cm$^{-2}$. This is coincident with the low FIR emission region. The ridges with the higher N(HI) values correspond to enhanced FIR emission regions.

We produced N(HI) plots for the region using data from the Leiden-Dwingeloo HI survey (Hartmann & Burton 1997, LDS) in order to confirm the HI distribution measured by Lieu (1996). The LDS was conducted with the 25-m radio telescope at Dwingeloo and the data we used cover the velocity range –459$<v_{lsr}<$+415 km s$^{-1}$ with a resolution of 1.03 km s$^{-1}$. The 25-m radio telescope has a 36’ half-power beam and the survey was performed with 0$^{\circ}$.5 spacings. 