Determining the Nature of Dark Matter with Astrometry

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Determining the Nature of Dark Matter with Astrometry Louie Strigari UC Irvine Center for Cosmology Fermilab, 4.16.

1 Determining the Nature of Dark Matter with Astrometry Louie Strigari UC Irvine Center for Cosmology Fermilab, Collaborators: James Bullock, Juerg Diemand, Manoj Kaplinghat, Michael Kuhlen, Piero Madau, Steve Majewski, Ricardo Munoz

2 Dark Matter in Cosmology Standard WIMP Cold Proliferation of candidates astrophysical implications The `nature of dark matter Non-baryonic dark matter Ωh 2 = ±0.009 not hot cold vs warm Is warm interesting?

(radial and mass) Structure of Dark Matter Halos Leo I High

3 Astrophysical Constraints on Dark Matter Low mass field galaxies: rotation curves Milky Way Satellites Number counts Distribution (radial and mass) Structure of Dark Matter Halos Leo I High Precision data sets: What can we learn in the future? What can we learn now?

4 CDM: Cosmological Consequences Hundreds of dark matter-dominated Milky Way satellite galaxies [Klypin et al, Moore et al 1999] Dark mini-halos abundance in the central regions [Diemand et al 2006] CDM free streaming: structure down to earth mass scales Orders of magnitude more dark subhalos than observed satellites of MW or M31: the missing satellites problem

5 CDM: Cosmological Consequences Halo density profile scaling as 1/r in the central regions [Navarro et al 2004, Diemand et al 2004] cusp Phase-space density, Q = ρ/σ 3, is enormous $ m Q CDM " 7 #10 14 cdm ' & ) % 100GeV ( 3 / 2 M sun pc *3 (km /s) *3 core Low mass dark matter halos may be less `cuspy than predicted in CDM Simon et al. 2005, Kuzio de Naray 2006

6 A standard fix: Warm dark matter Dark matter freezes out with nonnegligible velocities Free streaming: Reduces the number of small halos Cosmological Constraints Narayan et al 2000: m WDM > 750 ev Viel et al 2005: m WDM > 550 ev New data and analysis Seljak et al 2006 Viel et al 2006 Abazajian 2006

7 Warm dark matter: Cosmological Consequences Less dense dark matter halos Reduced phase space density % m ( Q " 5 #10 $4 ' * & kev ) 4 M sun pc $3 (km /s) $3 [Tremaine-Gunn Bound] Are the dynamics of dwarf galaxies set by dark matter physics? Hogan & Dalcanton 2000

8 Some other Cosmological Fixes (Crude list) Inflaton Potential (Kamionkowski & Liddle 1999) Zentner & Bullock 2003 Self-Interacting Dark Matter (Spergel & Steinhardt 2000) Q-balls (Kusenko & Steinhardt 2001) Fuzzy Dark Matter (Hu et al. 2001) Annihilating Dark Matter (Kaplinghat, Knox & Turner 2001) (See also Beacom, Bell & Mack 2006) Decaying Dark Matter (Sanchez-Salcedo 2003, Cen 2000) Can we `fix small scale structure and still connect dark matter to weak scale physics?

Dark Matter from Early Decays (SuperWIMPs) What if dark matter freezes-out, then decays to a `superweakly interacting particle? Large velocity at production: 0.

9 Dark Matter from Early Decays (SuperWIMPs) What if dark matter freezes-out, then decays to a `superweakly interacting particle? Large velocity at production: 0.1-1c Free-streaming scale: Q -1/3 Reduced Phase-Space Density % 10 #3 Q "10 #6 ' & $m /m DM ( * ) 3 % zdecay ( ' * & 1000) 3 M sun pc #3 (km /s) #3 Is dark matter from decays just a one-parameter family of models? Cembranos et al., Kaplinghat (2005)

10 Dark matter from late decays Mass splitting is a free parameter: what if they are of order GeV? (Universal Extra Dimensions) Free-streaming scale now depends on the lifetime: Q -1/3 τ -1/3 (Meta-CDM) Lifetime: sec. Lifetime: sec. Neutrino WDM Also, dark matter in UED or SUSY may be decaying now [Cembranos, Feng, LS 2007] LS, Kaplinghat, Bullock 2006

11 MeV Dark Matter Motivations: 511 kev emission from Galactic bulge Cutoff scale of about solar mass Interesting models give truncated power spectra. Limits/systematics up for debate Hooper,Kaplinghat,LS,Zurek

Census of Milky Way Satellites (Circa 2003) Name orbital radius (kpc) Discovered LMC 50 1519 SMC 60 1519 Sculptor 80 1937 Fornax 138 1938 Leo II 205 1950 Leo I 250 1950 Ursa Minor 66

12 Census of Milky Way Satellites (Circa 2003) Name orbital radius (kpc) Discovered LMC SMC Sculptor Fornax Leo II Leo I Ursa Minor Draco Carina Sextans Sagittarius Possible that up to 3x more exist at these luminosities [e.g. willman et al 2004] About a dozen satellites of M31

13 Census of Milky Way Satellites (Circa 2007) Name orbital radius (kpc) Discovered LMC SMC Sculptor Fornax Leo II Leo I Ursa Minor Draco Carina Sextans Sagittarius Canis Major Ursa Major I Willman I Bootes Canes Venatici I Canes Venatici II Coma Leo IV Hercules Leo T Belokurov et al. 2006

14 Dwarf Spheroidal Kinematics No rotation, dynamically supported by velocity dispersion Information on DM halo from line of sight velocities Not subject to the same systematics as rotation curves Walker et al 2006

15 The parameter space Jeans equations: At least 5 parameters Log-slope Cusps remain cusps even accounting for tidal interactions [Kazantzidis 2004, Dehnen 2005] Is there no dark matter in dwarf galaxies? [Kroupa et al. 2005]

16 Observational Inputs We take as inputs the density of stars Errors due to distance to galaxies not important

17 Line of sight velocity dispersion Fornax Cannot distinguish cores from cusps Strigari et al Fornax interesting because of the population of globular clusters [Goerdt et al 2006]

18 What can we learn from dwarfs? Velocity Anisotropy Truth = core Truth = cusp

19 Transverse velocities of stars Require accuracy on stellar transverse velocities of 5 km/s At < 100 kpc, this corresponds to accuracy 10 micro-arcseconds/yr R ϕ

Astrometry 101 Adapted from: http://planetquest.jpl.nasa.gov/sim/sim_index.cfm Bessel detected it in 1838 (< 0.5 arcsec). Nearest star (Proxima Cen) 0.

20 Astrometry 101 Adapted from: Bessel detected it in 1838 (< 0.5 arcsec). Nearest star (Proxima Cen) 0.77 arcsec Astronomy = star naming Astrometry = star measuring SIM uses interferometers in space to measure angles between celestial objects with incredible accuracy SIM PlanetQuest

21 SIM PlanetQuest (Space Interferometry Mission) SIM Positional Error Circle (4µas) Reflex Motion of Sun from 100pc (axes 100 µas) Hipparcos Positional Error Circle (0.64 mas). Parallactic Displacement of Galactic Center HST Positional Error Circle (~1.5 mas) Apparent Gravitational Displacement of a Distant Star due to Jupiter 1 degree away

22 Previous Considerations Wilkinson et al 2000 use a two-parameter model for the DM density profile They determine that the inner slope is well-constrained However, their model is not general enough. The inner slope is not well-constrained, even with proper motions

23 Constraints with SIM LS, Bullock, Kaplinghat ApJL 2007

24 Breaking the degeneracy

25 Optimizing observations Goal: SIM key project would entail 1000 hrs of observing time 200 stars from multiple dsphs

26 What can we learn now? [Semi-analytic models of, e.g. Bullock et al 2000, Kravtsov et al 2004, Moore et al 2006, Gnedin & Kravtsov 2006] -Stoehr et al 2002 suggest all of the MW satellites reside in the most massive subhalos Diemand, Kuhlen, Madau 2007

27 Constraints on galaxy masses

28 Redefining the Missing Satellites Problem -MW satellite population does not reside in the most massive CDM halos LS, Bullock, Kaplinghat, Diemand, Kuhlen, Madau 2007

29 Redefining the Missing Satellites Problem MW satellites could be either: -Earliest forming dark matter halos -Largest halos before accrection [See, e.g. semi-analytic models of Bullock et al 2000, Kravtsov et al 2004, Moore et al 2006, Gnedin & Kravtsov 2006] LS, Bullock, Kaplinghat, Diemand, Kuhlen, Madau 2007

30 Further Applications: Dark Matter Annihilations LS, Koushiappas, Bullock, Kaplinghat 2007

31 With substructure, fluxes may be boosted LS, Koushiappas, Bullock, Kaplinghat 2007

32 Conclusions and Outlook Proliferation of interesting dark matter models to constrain with galaxy dynamics. Escape the tyranny of CDM! Dwarf galaxies provide a unique test of dark matter At present, can t distinguish between cores and cusps. This will change with astrometric measurements. Present data strongly constrains mass of galaxies within about 600 kpc. This can be used to rule out the hypothesis that the present MW satellites reside in the most massive subhalos New constraints for dark matter annihilations. Louie Strigari UC Irvine

Distinguishing Between Warm and Cold Dark Matter

Distinguishing Between Warm and Cold Dark Matter Center for Cosmology Aspen Workshop Neutrinos in Physics & Astrophysics 2/2/2007 Collaborators: James Bullock, Manoj Kaplinghat astro-ph/0701581.. Motivations