Niayesh Afshordi Western University Friday April 13 2012 Friday the 13th is a date considered to be bad luck in Western superstition Wikipedia Outline Introduction Cold Dark Matter CDM ID: 1045517
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1. Tales of Dark Matter on Small ScalesNiayesh AfshordiWestern UniversityFriday, April 13, 2012
2. “Friday the 13th is a date considered to be bad luck in Western superstition.” -Wikipedia.
3. OutlineIntroduction: Cold Dark Matter (CDM) Why phase space of CDM haloes is hierarchicalToo big to Fail? A Tale of Small ScaleBound Structures & CDM detectionFuture Prospects for dark matter astronomy
4. Roya Mohayaee (IAP, Paris) Ed Bertschinger (MIT)Kathryn Zurek (U-Michigan)Louis Strigari (Stanford)Shant Baghram (U-Waterloo/PI)NA, Mohayaee, Bertschinger: Phys.Rev.D79:083526,2009 NA, Mohayaee, Bertschinger: Phys.Rev.D81:101301, 2010Baghram, NA, Zurek: Phys.Rev.D84:043511,2011Baghram, NA, Strigari: in preparationCollaborators
5. OutlineIntroduction: Cold Dark Matter (CDM) Why phase space of CDM haloes is hierarchicalToo big to Fail? A Tale of Small ScaleBound Structures & CDM detectionFuture Prospects for dark matter astronomy
6. Bullet Cluster Baryons (X-ray) Matter (lensing)Dark Matter is Collisionless
7. Dark Matter is ColdZaldarriaga & Tegmark 2002
8. Indirect DetectionDark Matter can annihilate tophotons (Fermi)electrons/positrons (PAMELA/Fermi/WMAP…Planck)Neutrinos (IceCube)Springel, et al. 08
9. Directional DM detectionSolar system is moving towards the Cygnus constellation in the Milky Way, at 220 km/s We should see a DM wind coming from Cygnus, which distinguishes it from any other backgroundSciolla et al 2008250 km/s
10. WIMPs: from gravity to detectionGravitational evidence for DM comes from potential: d3x ρ(x)/|x-x’|Direct detection: ρ(x) at solar systemIndirect detection (annihilation): d3x ρ(x)2WIMP detection is much more sensitive to DM sub-structure: Boost = <ρ2>/<ρ>2-1Boost to annihilation signal (indirect detection) (e.g., Taylor & Silk 2003)Variance for direct detection(e.g., Stiff, Widrow, & Frieman 2001)
11. OutlineIntroduction: Cold Dark Matter (CDM)Why phase space of CDM haloes is hierarchicalToo big to Fail? A Tale of Small ScaleBound Structures & CDM detectionFuture Prospects for dark matter astronomy
12. Hierarchy in the Phase spaceCDM is really cold vCDM ~ 10-11cPhase space density remains constant in lieu of collisions (Liouville’s Theorem): At CDM freeze out: Within our Galaxy:Most of the phase space is empty!Structures on all scales!!??
13. Hierarchical Micro-Structure of the Phase Spacetime
14. Bound sub-haloes (cluster in real/phase space)Tidal debris (cluster in initial conditions)Fundamental discreteness analogous to galaxy shot noise (NA, Mohayaee, Bertschinger 2009; Vogelsberger & White 2011)Three types of phase structuresNGC 3923Kuhlen, Diemand, et al. Hayashi et al. 2003
15. Correlation Functions quantify Hierarchy Large Scale Structure Projected Correlation Function SDSS Masjedi, et al. unbound structurebound substructurePhase Space Correlation Function
16. OutlineIntroduction: Cold Dark Matter (CDM) Why phase space of CDM haloes is hierarchicalToo big to Fail? A Tale of Small ScaleBound Structures & CDM detectionFuture Prospects for dark matter astronomy
17. Courtesy of Shant Baghram: http://pirsa.org/12040110/Too Big to Fail Problem?Subhalos in are dynamically can not host the most luminous dwarf satellites of Milky Way: (Too big to fail?) (Michael Boylan-Kolchin, James S. Bullock, Manoj Kaplinghat, arXiv :1103.0007)Aquarius simulation: high resolution simulation of 6 Milky- way type halo Baghram, NA, & Strigari, in prep.
18. *Binning in the Energy and Angular momentum*Non- smooth phase-space densityNow we can rewrite the observable density of stars, by plugging the phase space density function definition as :Marginalize over fab’sEL Number of binning = number of free parametersTricks of the Trade!
19. OutlineIntroduction: Cold Dark Matter (CDM) Why phase space of CDM haloes is hierarchicalToo big to Fail? A Tale of Small ScaleBound Structures & CDM detectionFuture Prospects for dark matter astronomy
20. Bound SubstructuresSmall sub-haloes become resilient to tidal strippingStable clustering hypothesis:# of pairs at small physical separation remains constant (Davis & Peebles 77)We extend this to the phase spaceUnlike the halo model, captures the full hierarchy: sub-haloes, sub-sub-haloes, etc. (also much fewer parameters)
21. sub-haloes and stable clusteringStable clustering in phase space can be used to describe bound subn-halo hierarchyKuhlen, Diemand, et al. Boost » 106 (½crit,0/½)NA, et al. 20100.03Standard deviation of linear overdensity on mass scale M
22. DM annihilation profile:stable clustering vs. simulationssmooth haloM(<r)/M200Bound substructure+tidal cut-offMsub > 105MMsub > 106MMsub > 107MMsub > 108MSpringel, et al. 08Annihilation Luminosity (<r)
23. Massaging the tidal stripping prescription …
24. sub-haloes in Direct Detection!Temporal auto-correlation of DM detection in several years…
25. Dark Matter Astronomy?From bound subhaloes:Boost = O(1) = density variance @ solar radiusLocal DM wind may NOT come from the direction of Cygnus!Phase space correlation will be probed by directional DM detectionunbound structurebound substructureHansen et al. 2005, Vogelsberger et al. 2009, Kuhlen et al. 2010
26. Dark Matter subhaloes may even impact Pulsar Timing Hertzberg, Siegel, Fry 2007
27. Dark Matter subhaloes may even impact Pulsar Timing Doppler EffectShapiro DelayBaghram, NA, & Zurek, 2011log(Pulsar residual power spectrum)log(Pulsar residual power spectrum)
28. LessonsCDM has lots of structure on small scales:Boost in DM annihilation Time dependence in direct detection signalRich structure for directional DM detectionPotentially detectable Pulsar Timing residualsCorrelation Function in Phase Space is a Powerful tool ( stable clustering)Measuring Dark Matter masses from stellar kinematics is a tricky business
29. Two Cautionary Notes…What about baryons?They can enhance CDM structures through adiabatic contraction, or destroy them via gravitational collisions/heatingReal haloes are almost certainly more complicated!Why not just extrapolate simulations?Simulations are NOT scale-free tidal limitNeither is CDM over 10 orders of magnitude!