The inner structure of haloes in Cold+Warm dark matter models
Possible Evidence of Thermodynamic Activity in Dark Matter Haloes.
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Transcript of Possible Evidence of Thermodynamic Activity in Dark Matter Haloes.
![Page 1: Possible Evidence of Thermodynamic Activity in Dark Matter Haloes.](https://reader030.fdocuments.net/reader030/viewer/2022033103/56649f2b5503460f94c45c51/html5/thumbnails/1.jpg)
Possible Evidence of Thermodynamic Activity in Dark Matter Haloes
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Universal feature of galactic haloes : Flat rotation curves
Flat rotation curves naturally appear if source is a self-gravitating isothermal Boltzmann gas.
A coincidence?
Circular orbits +
Spherical symmetry +
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Now recall basic thermo undergrad homework problem: find density profile of the
atmosphere
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Standard treatment of dark matter haloes N particle simulations
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Standard treatment of dark matter haloes N particle simulations
Navarro-Frenk-White
Simulation-inspired density profiles: Einasto
...and many others give reasonable fits to rotation curve data
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Standard treatment of dark matter haloes N particle simulations
Navarro-Frenk-White
Simulation-inspired density profiles: Einasto
...and many others give reasonable fits to rotation curve data
Thermodynamics
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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
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• 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 Structure
Sean Tulin, Hai-Bo Yu, Kathryn M. Zurek, arXiv:1302.3898
• Is equilibrium possible?
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A closer look at rotation curves: Using simplifying assumptions, both density and potential can be determined directly.
Newton
Poisson
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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
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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
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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
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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
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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
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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
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NGC 3198 • Disk distance scale = 2.68 kpc, data available up to 38 kpc• H gas mass is approximately 29% of the disk mass
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Moral: coincidence with Boltzmann gas for large portions of haloes - even though rotation curves not exactly flat.
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
Breakdown of Boltzmann description at small and large distances
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NGC 2841 NGC 5055 NGC 7331
NGC 2903 NGC 2403 NGC 3521
NGC 3198
Boltzmann fits
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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?
many improvements possible:
• drop spherical symmetry• include H gas, disk contributions• extend to galaxy interior – test quantum statistics
CONCLUDING REMARKS