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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)


K. S. Dwarakanath (NRAO), J. H. van Gorkom (Columbia), F. N. Owen (NRAO)

We present a VLA search for neutral hydrogen in three clusters, which are considered to be prime examples of so called cooling flow clusters, Virgo (Virgo A), Abell 2199 (3C 338) and Abell 780 (Hydra A). We looked for HI in absorption against the central radio sources with a velocity coverage $\sim$ 2600 km s$^{-1}$ and with a velocity resolution $\sim$ 87 km s$^{-1}$. We do not detect a spatially extended distribution of cold clouds. Our 3 $\sigma$ optical depth limits are 0.0005 over a typical velocity range of 500 km s$^{-1}$. Assuming the currently popular cooling flow scenarios in which the distribution of the cold gas can be characterized by a core radius of about 100 kpc, our results place a 3 $\sigma$ upper limit of 1.2 $\times$ 10$^{10}$~M$_{\odot}$ ~ to the mass of neutral hydrogen in such a flow for an assumed spin temperature of 100 K. This limit is a factor of 30 below what is expected from the Einstein Solid State Spectrometer observations of cooling flow clusters and is 1 - 2 orders of magnitude below what is expected from the cooling flow models. The expected large amount of HI is unlikely to exist in these clusters even as optically thick clouds unless the spin temperature is less than 10 K and / or the covering factor is much less than 1. We discuss some physical conditions in which such large amounts of HI could have escaped detection.

We do however find HI absorption against the core of Hydra A. This line is narrow ($\sim$50 km s$^{-1}$) and is not seen against the extended radio lobes. The properties of this absorption system are similar to those seen in some other cooling flow clusters and in isolated radio galaxies. We also detect a spiral galaxy in A 2199 with a total mass of 1.8 $\times$ 10$^{9}$ M$_{\odot}$.

Despite this detection of what might be a small HI cloud near the systemic velocity of the core of Hydra A, we do place stringent limits on the existence of such clouds anywhere within the primary beam. The upper limit to HI emission from such clouds ranges from 10$^{7}$ - 10$^9$ M$_{\odot}$.

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