Hubble Space TelescopeSTIS Spectroscopy of the Lyα Emission Line in the Central Dominant Galaxies in A426, A1795, and A2597: Constraints on Clouds in the Intracluster Medium

We report on HST/STIS spectra of the Lyman-alpha emission in the centraldominant galaxies in three rich clusters of galaxies. We find evidence for apopulation of clouds in the intracluster medium.We detect 10 Ly-alphaabsorption systems towards the nucleus of NGC1275 with columns of N(HI)1E12-1E14 cm-2. The detected absorption features are most consistent withassociated nuclear absorption systems. There is very little nuclear absorptionat the systemic velocity in NGC1275. This implies that the large columnsdetected in the 21 cm line towards the parsec scale radio source avoid the lineof sight to the nucleus. This gas may be located in a circumnuclear disk ortorus. We detect at least one and possibly two absorption features towards theextended Ly-alpha in A426. We do not detect absorption towards the extendedLy-alpha emission in A1795, and A2597 with upper limits N(HI) 1E13 cm-2 foroptically thin absorbers. Our data constrain the covering factor of any highcolumn density gas in the ICM to be less than 25%. Our results suggest that thelack of observed intermediate temperature gas is not explained by obscuration.In addition, the low columns of gas on the 100 kpc scales in the ICM suggeststhat (1) the rate at which cold gas accumulates in the ICM on these scales isvery low, and (2) the dense nebulae in the central 10 kpc must have cooled orbeen deposited in situ.Comment: 6 figure