The Cold Absorber in Clusters of Galaxies: New ASCA \\ Observations and Models

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Session 74 -- Clusters of Galaxies II: X-Rays
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[74.07] The Cold Absorber in Clusters of Galaxies: New ASCA \\ Observations and Models

Michael W. Wise (MIT/ASC), Craig L. Sarazin (UVa)

One of the most persistent problems concerning cooling flows is the ultimate repository of the cooling gas. Recently, White et al. (1991) have found evidence for excess soft X--ray absorption in the spectra of a sample of cluster cooling flows observed with the $Einstein$ SSS. The typical excess columns of cold material (in excess to the galactic column $N_H$) are $\Delta N_H \sim 10^{21}$ cm$^{-2}$. When these columns are accumulated over the area of the cooling flow, they imply the presence of very large quantities of cold absorbing material ($M_{cold} \sim 10^{11}$--$10^{12} \, M_{\odot}$). This soft X--ray absorption could represent the first direct evidence for the large amounts of cooled material which current cooling flow models predict.

We will present results from the analysis of a 45 ksec ASCA observation of the bright, relatively nearby ($z=0.0767$) cooling flow cluster A2029. Our preliminary analysis confirms both the strong cooling flow ($\dot M \sim 370 ~M_{\odot}$ yr$^{-1}$) as well as the presence of excess absorption at a level $\sim 5$ times the standard galactic column. The spectrum is reasonably well fit by a partial covering fraction absorption model with a covering fraction of $\sim$ 0.7. Models assuming simple galactic absorption are NOT consistent with the data. There is also evidence for an absorption feature at $\sim 0.49$ keV, consistent with the redshifted O K-edge one would expect from intrinsic absorption due to cold material.

In addition, we have constructed a grid of detailed models for the expected X--ray spectra and surface brightnesses of cluster cooling flows including the opacity due to accumulated cold material. These models indicate that derived values for the total cooling rate $\dot M$ may be underestimated by $\sim 2$ assuming 100\% of the cooling material goes into a cold, X--ray absorbing form. We find that models with higher mass deposition in the central regions can produce profiles comparable to the $\dot M(P>

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