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Abell 1795
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Title: A very deep Chandra observation of Abell 1795: The Cold Front and Cooling Wake 
Author: S.Ehlert, M.McDonald, E.D.Miller, L.P.David, M.W.Bautz 

We present a new analysis of very deep Chandra observations of the galaxy cluster Abell 1795. Utilising nearly 750 ks of net ACIS imaging, we are able to resolve the thermodynamic structure of the Intracluster Medium (ICM) on length scales of ~ 1 \kpc near the cool core. We find several previously unresolved structures, including a high pressure feature to the north of the BCG that appears to arise from the bulk motion of Abell 1795's cool core. To the south of the cool core, we find low temperature (~ 3 \keV), diffuse ICM gas extending for distances of ~ 50 \kpc spatially coincident with previously identified filaments of Halpha emission. Gas at similar temperatures is also detected in adjacent regions without any Halpha emission. The X-ray gas coincident with the Halpha filament has been measured to be cooling spectroscopically at a rate of ~ 1 \msolar \yr^{-1}, consistent with measurements of the star formation rate in this region as inferred from UV observations, suggesting that the star formation in this filament as inferred by its Halpha and UV emission can trace its origin to the rapid cooling of dense, X-ray emitting gas. The Halpha filament is not a unique site of cooler ICM, however, as ICM at similar temperatures and even higher metallicities not cospatial with Halpha emission is observed just to the west of the Halpha filament, suggesting that it may have been uplifted by Abell 1795's central active galaxy. Further simulations of cool core sloshing and AGN feedback operating in concert with one another will be necessary to understand how such a dynamic cool core region may have originated and why the Halpha emission is so localised with respect to the cool X-ray gas despite the evidence for a catastrophic cooling flow.


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Title: Cold Molecular Gas Along the Cooling X-ray Filament in Abell 1795
Authors: Michael McDonald, Lisa H. Wei, Sylvain Veilleux

We present the results of interferometric observations of the cool core of Abell 1795 at CO(1-0) using the Combined Array for Research in Millimetre-Wave Astronomy. In agreement with previous work, we detect a significant amount of cold molecular gas (3.9 ± 0.4 x10^9 solar masses) in the central ~10 kpc. We report the discovery of a substantial clump of cold molecular gas at clustercentric radius of 30 kpc (2.9 ± 0.4 x10^9 solar masses), coincident in both position and velocity with the warm, ionised filaments. We also place an upper limit on the H_2 mass at the outer edge of the star-forming filament, corresponding to a distance of 60 kpc (<0.9 x10^9 solar masses). We measure a strong gradient in the HII/H_2 ratio as a function of radius, suggesting different ionisation mechanisms in the nucleus and filaments of Abell1795. The total mass of cold molecular gas (\sim7x10^9 solar masses) is roughly 30% of the classical cooling estimate at the same position, assuming a cooling time of 10^9 yr. Combining the cold molecular gas mass with the UV-derived star formation rate and the warm, ionised gas mass, the spectroscopically-derived X-ray cooling rate is fully accounted for and in good agreement with the cooling by-products over timescales of \sim10^9 yr. The overall agreement between the cooling rate of the hot intracluster medium and the mass of the cool gas reservoir suggests that, at least in this system, the cooling flow problem stems from a lack of observable cooling in the more diffuse regions at large radii.

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