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Mass-Concentration Relation in Galaxy Clusters

Mass-Concentration Relation in Galaxy Clusters. -Jarron Leisenring. Outline. Cluster Formation Simulations CDM Halo Predictions Actual DM Halos Concentration-Mass Relationship Concentration Distribution Function Anomalously High Concentrations Conclusions. Cluster Formation Simulations.

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Mass-Concentration Relation in Galaxy Clusters

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  1. Mass-Concentration Relation in Galaxy Clusters -Jarron Leisenring

  2. Outline • Cluster Formation Simulations • CDM Halo Predictions • Actual DM Halos • Concentration-Mass Relationship • Concentration Distribution Function • Anomalously High Concentrations • Conclusions ASTR 836

  3. Cluster Formation Simulations • Lambda-CDM (85/10/5) • Structure formation • gravitational amplification of primordial density fluctuations • Clusters form where filaments intersect • Gas falls into deep potential well • heated to ~108 K by shocks and adiabatic compression • X-ray emission ASTR 836

  4. CDM Halo Predictions • Navarro-Frenk-White (NFW) models show shape of DM halos • Independent of • halo mass • cosmological parameters • initial power spectrum ASTR 836

  5. Actual DM Halos Observations agree w/ simulations • Dwarf and LSB galaxies • Galaxy clusters A few problems though • “Cuspy core problem” • HI Rotation curves suggest flatter central density profile • A few X-ray and lensing observations find density profile steepens for radii larger than rs ASTR 836

  6. Concentration-Mass Relationship • Halo concentration • Ratio of virial radius to scale radius • Proxy for central density • Mass • Taken to be within virial radius • Simulations predict concentration gradually decreasing with cluster mass (Hennawi 2007) • observations have yet to confirm ASTR 836

  7. Concentration-Mass Relationship • Observational sample consists of 100 galaxy clusters • Broad distribution of cluster concentrations • Separate into 4 mass bins and fit power law • Slope consistent with simulations • Larger normalization, though ASTR 836

  8. Concentration-Mass Relationship • Observational sample consists of 100 galaxy clusters • Broad distribution of cluster concentrations • Separate into 4 mass bins and fit power law • Slope consistent with simulations • Larger normalization, though ASTR 836

  9. Concentration-Mass Relationship • Variety of techniques to find concentration • Lensing methods show systematically higher concentrations than X-Ray ASTR 836

  10. Concentrations for Fixed Halo Masses • Simulations suggest log-normal distribution for concentrations • Not observed prior • Two exceptions • Removal improves χ2 by up to a factor of 6 ASTR 836

  11. Anomalously High Concentrations • Most likely due to halo elongation, substructure, and/or adiabatic contraction ASTR 836

  12. Conclusions • Concentration-mass relationship best fit by a power law with a slope consistent with the simulation value of -0.13. • Normalization is at least 20% higher than simulations • Effects from adiabatic contraction and a steepening of the dark matter density profile • Concentrations for lensing are higher than for X-ray temperatures • X-ray under-predicts for unrelaxed clusters and lensing over-predicts due to halo triaxiality and line of sight structure • Log-normal distribution of clusters predicted by simulations is confirmed observationally ASTR 836

  13. Future Work • Ray tracing the Millennium simulation • Best comparison to date • Ample statistics all four mass bins ASTR 836

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