Detection of Extended HI Absorption in Abell 2597

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Session 53 -- Cluster Cooling Flows and Abundances
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[53.06] Detection of Extended HI Absorption in Abell 2597

C. P. O'Dea, S. A. Baum (STScI), J. Gallimore (STScI and U. Maryland)

We report the detection of extended HI in absorption against the bright radio source PKS~2322--123 in the cD galaxy in the `cooling flow' cluster A2597. We used the VLA in the A configuration with $2.3\times 1.5$ arcsec spatial resolution and at two velocity resolutions centered at the systemic velocity of the cD (z=0.082) (1) 48 km/s velocity resolution over a range of 1304 km/s and (2) 1.5 km/s over a range of 524 km/s. The HI profile has a FWHM of $\sim 410$ km/s and a peak optical depth of $\tau \simeq 0.0056$ and is centered near the systemic velocity of the cD. We derive a lower limit to the covering factor of the HI clouds in front of the radio source of $c_f > 0.006$. We have sufficient signal-to-noise to detect the HI over the bright inner parts of the radio source with extent $\sim 4"$ (5.6 kpc). The estimated mass in the HI is about an order of magnitude larger than that inferred in the H$\alpha$ emitting filaments (over the same region) suggesting that the nebula is photon bounded rather than matter bounded. The (1) broad velocity width of the HI (which is similar to the H$\alpha$), (2) the extended nature of the HI, and (3) the result that the nebula is photon bounded are all consistent with the hypothesis that the H$\alpha$ filaments are the ionized skins of a population of HI clouds. If this is the case then we can combine the optically derived volume filling factor with the radio derived covering factor to place limits on the cloud radius of $ 0.02 < r_{cl} < 4$ pc.

We also detect a narrower (FWHM $\sim 220$ km/s) deeper ($\tau \simeq 0.019$) spatially unresolved ($< 2$ kpc) component towards the nucleus only which is redshifted by about 300 km/s and thus represents material infalling towards the nucleus. This gas is kinematically and spatially distinct from the extended HI and might have been acquired from a merger/interaction.

We discuss these results in the context of current models for the optical and x-ray emission from `cooling flow' clusters.

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