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Galaxies and the Universe - Hot Gas in Clusters

Galaxies and the Universe - Hot Gas in Clusters - Gala ie...

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1/15/12 Gala[ieV and Whe UniYeUVe - HoW GaV in ClXVWeUV 1/6 ZZZ.aVWU.Xa.edX/keel/gala[ieV/icm.hWml ="+3"> HoW GaV in ClXVWeUV of Gala[ieV VelociW\ diVpeUVionV VXggeVW WhaW aboXW 90% of Whe maVV in clXVWeUV iV noW in indiYidXal gala[ieV. AmoXnWV of maVV compaUable Wo WhaW in Whe gala[ieV (bXW noW Whe d\namical WoWal) aUe implied b\ X-Ua\ emiVVion fUom hoW gaV and Uadio "WailV" benW b\ gala[\ moWion WhUoXgh an inWUaclXVWeU mediXm. Cluster X-ra\ sources haYe been UeYieZed b\ FoUman and JoneV 1982 (ARA&A 20, 547) and SaUa]in 1986 (ReY. Mod. Ph\V. 58, 1). The gaV haV WempeUaWXUe 4-7 keV coUUeVponding Wo Whe WempeUaWXUe aVVociaWed ZiWh Whe clXVWeU YelociW\ diVpeUVion and VpecWUa conViVWenW ZiWh WheUmal bUehmVVWUahlXng. The gaV iV noW XVXall\ aVVociaWed ZiWh indiYidXal gala[ieV, XnleVV a dominanW one iV aW Whe cenWeU of Whe clXVWeU poWenWial: fUom Fig 1 of FoUman and JoneV (Waken fUom Whe ADS), one can Vee Whe Uange in X-Ua\ moUphologieV, fUom Whe diVpeUVed and iUUegXlaU moUpholog\ of Whe clXVWeUV on Whe lefW Wo Whe incUeaVingl\ concenWUaWed foUmV on Whe UighW. Since iW'V illegible on Whe Vcan, Whe lefW colXmn conWainV A1367, SC 0627-54, and A2256, Zhile on Whe UighW Ze Vee A262, 2199 (a pUominenW cD clXVWeU), and 85. TheUe'V a laUge collecWion of opWical/X- Ua\ compaUiVonV aYailable among Ra\ WhiWe'V clXVWeU mXg VhoWV ThiV XMM-NeZWon YieZ of Whe Coma clXVWeU VhoZV Whe inWeUnal VWUXcWXUe of eYen VXch a Uich and Uela[ed aVVemblage (ESA image):
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1/15/12 Gala[ieV and Whe UniYeUVe - HoW GaV in ClXVWeUV 2/6 ZZZ.aVWU.Xa.edX/keel/gala[ieV/icm.hWml The X-ray spectra reveal lines of highly ionized Fe, indicating that the gas has been processed - it came from galaxies early on, rather than being primordial. The galaxy motions in the cluster are an ample (but perhaps not the only) heating source, since kT a m p Y 2 . A typical velocity dispersion 700 km/s implies T a 6 x 10 7 K from this source alone. Extra heating sources may be sought from the correlation between velocity dispersion and ICM temperature, or considering the specific entropy of the gas. The hot gas has a very long cooling time (of order the Hubble time) except in denser areas, which can produce a cooling floZ onto individual galaxies or in cluster cores. This happens because of the interesting behavior of the cooling rate for hydrogen-dominated plasmas as a function of temperature and density; since brehmsstrahlung is important, the n e 2 dependence can pull the rug out from under a pressure-supported gas. That is, for a purely cooling plasma, the time it spends
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Galaxies and the Universe - Hot Gas in Clusters - Gala ie...

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