The space among galaxies is not as empty.
Astrophysical evidences of the Intracluster Medium (ICM) and the Intergalactic Medium (IGM).
ICM: Intense X-ray diffuse emission.
Emission lines from ionized iron.
Chemical abundances in the ICM.
Temperature of the hot gas in the galaxy clusters halos.
In rich clusters the hot intracluster medium is the dominant, luminous component of the mass.
Studies of the ICM yield information on a rich variety of phenomena.
ICM mass to the stellar mass is plotted against the temperature of the gas. Credit: David et al. (1988).
Distribution of hot gas (blue) and cool gas (red) in massive galaxy cluster MACSJ0717. Credit: NASA/Chandra.
The ICM behaves as a fully ionized plasma at temperature of about 7 keV.
Emissivity dominated by thermal bremsstrahlung.
The emissivity at frequency :
and : number density of electrons and ions.
: Gaunt factor.
Approximation for keV clusters.
By integrating, the X-ray luminosity:
Application to X-ray surveys.
By assuming that the ICM gas has the same dynamics as galaxies, the typical ICM temperature
: proton mass
: the mean molecular weight
(for a primordial composition)
Scaling relation for nearby and distant clusters and outliers.
Galaxy cluster mass estimate from X-ray data.
Assume: hydrostatic equilibrium, spherical symmetry.
Local gas pressure:
Local gas density:
: total gravitating mass within .
By inserting the equation of state for a perfect gas:
Application: measure the total gravitating cluster mass.
Comparison with theoretical models for cosmic structure formation.
Interaction of galaxies with the local cosmic environment.
Galaxy interaction with the hot ICM and a galaxy cluster gravitational field.
Proposed physical mechanisms:
Difficult observations of the on-going transformation.
The rich galaxy cluster Abell 2667 and the "comet galaxy" observed by the Hubble Space Telescope. Credit: NASA/ESA.
Ram pressure stripping (ICM)
: ICM density ;
: galaxy stellar and gas density
where is the scalelength of the exponential proﬁle.
P. Rosati et al. (2002): “Evolution of X-rays Clusters of Galaxies”, ARAA vol. 40, p. 539
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