Uniformity of foreground Galactic neutral Hydrogen over cooling flow clusters

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Abstract
Radio maps at 21 cm of foreground neutral hydrogen over three cooling flow clusters of galaxies show that the foreground gas is uniform on scales from about 1 -- 10 arcmin. Five sigma limits on fluctuations in the foreground column density for Abell 3581, Sersic 159-03 and Abell 2597 are 6.2e19, 7.8e19 and 4.3e19 per sq cm, or 14, 43 and 17 per cent of the mean foreground column density in the region of the system, respectively. Fluctuations in the column density of neutral gas in the Galaxy are unlikely to account for any excesses of photoelectric absorption in these or other cooling flow clusters. Fluctuations in the foreground neutral gas on arcminute scales are also unlikely to be the cause of excess EUV and soft X-ray emission from clusters.

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