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Astrophysics from Space Lecture 13: X-ray galaxy clusters

Astrophysics from Space Lecture 13: X-ray galaxy clusters. Prof. Dr. M. Baes (UGent) Prof. Dr. C. Waelkens (KUL) Academic year 2013-2014. Structure in the Universe. Major question in cosmology: how is matter distributed in the Universe ?

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Astrophysics from Space Lecture 13: X-ray galaxy clusters

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  1. Astrophysics from Space Lecture 13: X-ray galaxy clusters Prof. Dr. M. Baes (UGent) Prof. Dr. C. Waelkens (KUL) Academic year 2013-2014

  2. Structure in the Universe Major question in cosmology: how is matter distributed in the Universe ? Distribution of galaxies is way to investigate this

  3. Structure in the Universe • Enormous step forward since 1990s: galaxy redshift surveys • 2dF GRS • SDSS • Use Hubble’s law to reconstruct the 3D galaxy distribution. Galaxies are not distributed homogeneously in space. There are overdensities(groups, clusters) and underdensities(field, voids)

  4. Clustering of structure Quantitative measure of clustering: the largest scales on which the Universe is non-homogeneous are some 100 Mpc (superclusters).

  5. Clustering of structure

  6. Clustering of structure

  7. Clustering of structure

  8. Clustering of structure

  9. Clustering of structure

  10. Galaxy clusters • Most nearby galaxy clusters: • Virgo and Fornax (about 16 Mpc distance) • Virgo Cluster: • some 1300 member galaxies • total luminosity: 1.3 x 1012Lsun • physical size: several Mpc • Most nearby rich cluster: Coma (several times more luminous)

  11. Galaxy clusters Not just a collection of galaxies: complete well-defined structural entities. Look at X-ray emission: hot ICM. Galaxy clusters are the largest objects in the Universe with a well-defined structural shape and a proper equilibrium structure.

  12. X-ray galaxy clusters XMM-Newton and Chandra have been instrumental in detecting galaxy clusters, particularly at high z (current record holder is at z = 1.9 or t = 10.2 Gyr).

  13. Galaxy cluster mass determination • Hydrostatic equilibrium: • gravity (inwards) • gas pressure (outwards) • Can be applied to the intracluster gas to determine the mass distribution. If we know the temperature and the density distribution of the intracluster gas, we can determine the total mass distribution in the cluster.

  14. Gas density determination Origin of X-ray emission: thermal Bremsstrahlung Intensity of X-ray radiation is proportional to square of the gas density.

  15. Gas temperature determination Shape and line strenghts of the X-ray spectrum depend on temperature and chemical composition of the plasma. X-ray spectroscopy is needed to determine this (Chandra and XMM-Newton!)

  16. Example: Abell 1413

  17. Clusters mass budget • Fascinating result: the clusters mass budget • ICM : 11% • stars (galaxies) : 2% The bulk of the matter in galaxy clusters (>85%) consists of an unknown form of matter: dark matter. This actually accounts for the entire Universe…

  18. Energy content of the Universe Joint constraints from galaxy clusters, supernovae, CMB and H0 result in the so-called ΛCDM concordance model. Result: we don’t understand 95% of the Universe…

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