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Possible Evidence of Thermodynamic Activity in Dark Matter Haloes

Possible Evidence of Thermodynamic Activity in Dark Matter Haloes

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Possible Evidence of Thermodynamic Activity in Dark Matter Haloes

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  1. Possible Evidence of Thermodynamic Activity in Dark Matter Haloes

  2. A coincidence? Universal feature of galactic haloes : Flat rotation curves Flat rotation curves naturally appear if source is a self-gravitating isothermal Boltzmann gas. Circular orbits + Spherical symmetry +

  3. Now recall basic thermo undergrad homework problem: find density profile of the atmosphere

  4. Standard treatment of dark matter haloesN particle simulations

  5. Standard treatment of dark matter haloes N particle simulations Simulation-inspired density profiles: Navarro-Frenk-White Einasto ...and many others give reasonable fits to rotation curve data

  6. Standard treatment of dark matter haloes N particle simulations Thermodynamics Simulation-inspired density profiles: Navarro-Frenk-White Einasto ...and many others give reasonable fits to rotation curve data

  7. Equilibrium thermodynamics not considered in standard treatment of dark matter haloes • Relaxation times arising from gravitational interactions alone are too long (compared with the Hubble time) for thermodynamic equilibrium to be established. • If interactions other than gravity are present among the dark matter particles, they are too weak to establish thermal equilibrium. Bull%&t cluster • Rotation curves not exactly flat

  8. But issues remain for simulations eg., cusp at r=0, missing satellite problem • Strong bounds on dark matter-baryon interactions, -- not so for dark matter self-coupling • Self-couplings ( with interaction times < 1/H ) can cure simulation issues Observational evidence for self-interacting cold dark matter, David N. Spergel, Paul J. Steinhardt Phys.Rev.Lett. 84 (2000) 3760-3763 Beyond Collisionless Dark Matter: Particle Physics Dynamics for Dark Matter Halo StructureSean Tulin, Hai-Bo Yu, Kathryn M. Zurek,  arXiv:1302.3898 • Is equilibrium possible?

  9. A closer look at rotation curves: Using simplifying assumptions, • both density and potential can be determined directly. Newton Poisson

  10. NGC 2841 • Disk distance scale =3.5 kpc, data available up to 51.6 kpc (THINGS) • H gas mass is approximately 4% of the disk mass Series fit using

  11. NGC 5055 • Disk distance scale =3.622 kpc, data available up to 44.4 kpc (THINGS) • H gas mass is approximately 12.6% of the disk mass

  12. NGC 3521 • Disk distance scale =3.3 kpc, data available up to 35.5 kpc (THINGS) • H gas mass is approximately 11% of the disk mass

  13. NGC 7331 • Disk distance scale =3.2 kpc, data available up to 24 kpc (THINGS) • H gas mass is approximately 7% of the disk mass

  14. NGC 2403 • Disk distance scale =2.75 kpc, data available up to 24 kpc (THINGS) • H gas mass is approximately 19% of the disk mass

  15. NGC 2903 • Disk distance scale =3 kpc, data available up to 31 kpc (THINGS) • H gas mass is approximately 7% of the disk mass Series fit from 1 kpc to 31 kpc

  16. Disk distance scale = 2.68 kpc, data available up to 38 kpc • H gas mass is approximately 29% of the disk mass NGC 3198

  17. Moral: coincidence with Boltzmann gas for large portions of haloes - even though rotation curves not exactly flat. Breakdown of Boltzmann description at small and large distances • A simple model for Boltzmann region • Assume: • spherical symmetry • dynamics given by Emden eq. • gravitational attraction to • inner (baryonic) region • determined by boundary • conditions at r=R_g • leads to three-parameter family of solutions • get fits for

  18. Boltzmann fits NGC 2841 NGC 5055 NGC 7331 NGC 2903 NGC 2403 NGC 3521 NGC 3198

  19. CONCLUDING REMARKS • many improvements possible: • drop spherical symmetry • include H gas, disk contributions • extend to galaxy interior • – test quantum statistics If similarity with a Boltzmann gas not a coincidence, appears to indicate dark matter in thermal equilibrium. What can this tell us about dark matter self-interactions?