SIMBAD references

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 ∼1-10 arcmin. Five sigma limits on fluctuations in the foreground column density for Abell 3581, Sersic 159-03 and Abell 2597 are 6.2x10¹⁹, 7.8 x10¹⁹ and 4.3x10¹⁹ cm^–2, 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 arcmin scales are also unlikely to be the cause of excess extreme ultraviolet and soft X-ray emission from clusters.