louie strigari - university of california, irvinelstrigar/fermilabseminar.pdf · • astronomy =...
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Determining the Nature of Dark Matter with Astrometry
Louie StrigariUC Irvine
Center for Cosmology
Fermilab, 4.16.2007
Collaborators: James Bullock, Juerg Diemand, Manoj Kaplinghat, Michael Kuhlen,Piero Madau, Steve Majewski, Ricardo Munoz
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Dark Matter in Cosmology
Standard
WIMP
‘Cold’
Proliferation of candidates
astrophysical implications
The `nature’ of dark matter
not hot
cold vs warm
Is warm interesting?
Non-baryonic darkmatter
Ωh2 = 0.113 ±0.009
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Astrophysical Constraints on Dark Matter
Milky Way SatellitesNumber countsDistribution (radial and mass)Structure of Dark Matter Halos
Leo I
Low mass ‘field’ galaxies:rotation curves
High Precision data sets:
What can we learn in the future?
What can we learn now?
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CDM: Cosmological Consequences
Hundreds of dark matter-dominatedMilky Way satellite galaxies [Klypin etal, Moore et al 1999]
Dark mini-halos abundance in thecentral regions [Diemand et al 2006]
CDM free streaming: structure downto earth mass scales
Orders of magnitude more darksubhalos than observed satellites ofMW or M31: the ‘missing satellitesproblem’
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CDM: Cosmological Consequences
Simon et al. 2005, Kuzio de Naray 2006
cusp
core
Halo density profile scaling as 1/r inthe central regions [Navarro et al 2004,Diemand et al 2004]
Phase-space density, Q = ρ/σ3, isenormous
!
QCDM " 7 #1014mcdm
100GeV
$
% &
'
( )
3 / 2
Msun pc*3(km /s)
*3
Low mass dark matter halos maybe less `cuspy’ than predicted inCDM
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Dark matter freezes out with non-negligible velocitiesFree streaming: Reduces the numberof small halos
A standard fix: Warm dark matter
• Narayan et al 2000: mWDM > 750 eV• Viel et al 2005: mWDM > 550 eV• New data and analysis
Seljak et al 2006Viel et al 2006
Abazajian 2006
Cosmological Constraints
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Warm dark matter: Cosmological Consequences
Less dense dark matter halosReduced phase space density
Hogan & Dalcanton 2000
!
Q " 5 #10$4m
keV
%
& '
(
) *
4
Msun pc$3(km /s)
$3
[Tremaine-Gunn Bound]
Are the dynamics of dwarfgalaxies set by dark matterphysics?
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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 connectdark matter to weak scale physics?
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Dark Matter from Early Decays (SuperWIMPs)
!
Q "10#610
#3
$m /mDM
%
& ' '
(
) * *
3
zdecay
1000
%
& '
(
) *
3
Msun pc#3(km /s)
#3
Cembranos et al., Kaplinghat (2005)Is dark matter from decays just aone-parameter family of models?
What if dark matter freezes-out,then decays to a `superweaklyinteracting particle?’
Large velocity at production: 0.1-1c
Free-streaming scale: Q-1/3
Reduced Phase-Space Density
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Dark matter from late decays
LS, Kaplinghat, Bullock 2006
Lifetime: 1014 sec.
Lifetime: 1012 sec.
Neutrino WDM
Also, dark matter in UED or SUSYmay be decaying ‘now’ [Cembranos, Feng, LS 2007]
Mass splitting is a freeparameter: what if they are oforder GeV? (Universal ExtraDimensions)
Free-streaming scale nowdepends on the lifetime: Q-1/3 τ-1/3
(Meta-CDM)
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MeV Dark Matter
Hooper,Kaplinghat,LS,Zurek
Motivations: 511 keVemission from Galacticbulge
Cutoff scale of about105-106 solar mass
Interesting models givetruncated power spectra.Limits/systematics up fordebate
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Census of Milky Way Satellites (Circa 2003)
Name orbital radius (kpc) DiscoveredLMC 50 1519SMC 60 1519Sculptor 80 1937Fornax 138 1938Leo II 205 1950Leo I 250 1950Ursa Minor 66 1954Draco 80 1954Carina 101 1977Sextans 86 1990Sagittarius 5 1994
About a dozen satellites of M31
Possible that up to 3x more exist at these luminosities [e.g. willman et al 2004]
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Census of Milky Way Satellites (Circa 2007)
Name orbital radius (kpc) DiscoveredLMC 50 1519SMC 60 1519Sculptor 80 1937Fornax 138 1938Leo II 205 1950Leo I 250 1950Ursa Minor 66 1954Draco 80 1954Carina 101 1977Sextans 86 1990Sagittarius 5 1994Canis Major 80 2003Ursa Major I 100 2005Willman I 40 2005Bootes 62 2006Canes Venatici I 220 2006Canes Venatici II 150 2006Coma 40 2006Leo IV 160 2006Hercules 140 2006Leo T 420 2007
Belokurov et al. 2006
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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
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The parameter space
At least 5 parameters
Jeans equations:
• Cusps remain cusps even accounting for tidal interactions[Kazantzidis 2004, Dehnen 2005]
• Is there no dark matter in dwarf galaxies? [Kroupa et al. 2005]
Log-slope
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Observational Inputs
• We take as inputsthe density of stars
• Errors due todistance to galaxiesnot important
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Strigari et al. 2006Cannot distinguish cores from cusps
Fornax interesting because of the population of globular clusters[Goerdt et al 2006]
Line of sight velocity dispersion
Fornax
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What can we learn from dwarfs?
Truth = core Truth = cusp
Velo
city
Aniso
trop
y
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R
ϕ
Transverse velocities of stars
•Require accuracy onstellar transversevelocities of 5 km/s
•At < 100 kpc, thiscorresponds to accuracy10 micro-arcseconds/yr
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Astrometry 101
SIM PlanetQuest
• Astronomy = “star naming”• Astrometry = “star measuring”• SIM uses interferometers in space to
measure angles between celestial objectswith incredible accuracy
Adap
ted
from
: ht
tp:/
/pla
netq
uest
.jpl.n
asa.
gov/
SIM
/sim
_ind
ex.c
fm
Bessel detected it in 1838 (< 0.5 arcsec).Nearest star (Proxima Cen) 0.77 arcsec
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Reflex Motion of Sunfrom 100pc (axes 100µas)
ParallacticDisplacementof GalacticCenter
Apparent GravitationalDisplacement of aDistant Star due toJupiter 1 degree away
SIM PlanetQuest (Space Interferometry Mission)
SIM PositionalError Circle
(4µas)
.HipparcosPositionalError Circle(0.64 mas)
HST Positional ErrorCircle (~1.5 mas)
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Previous Considerations
• Wilkinson et al 2000 use atwo-parameter model for theDM density profile
• They determine that theinner slope is well-constrained
• However, their model is notgeneral enough. The innerslope is not well-constrained,even with proper motions
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Constraints with SIM
LS, Bullock, Kaplinghat ApJL 2007
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Breaking the degeneracy
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Optimizing observations
Goal: SIM key projectwould entail 1000 hrs ofobserving time
200 stars frommultiple dSphs
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What can we learn now?
Diemand, Kuhlen, Madau 2007
[Semi-analytic models of,e.g. Bullock et al 2000,Kravtsov et al 2004,Moore et al 2006,Gnedin & Kravtsov 2006]
-Stoehr et al 2002suggest all of the MWsatellites reside in themost massive subhalos
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Constraints on galaxy masses
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Redefining the Missing Satellites Problem
LS, Bullock, Kaplinghat, Diemand, Kuhlen, Madau 2007
-MW satellitepopulation does notreside in the mostmassive CDM halos
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LS, Bullock, Kaplinghat, Diemand, Kuhlen, Madau 2007
MW satellites could beeither:
-Earliest forming darkmatter halos
-Largest halos beforeaccrection
[See, e.g. semi-analyticmodels of Bullock et al2000, Kravtsov et al2004, Moore et al 2006,Gnedin & Kravtsov 2006]
Redefining the Missing Satellites Problem
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Further Applications: Dark Matter Annihilations
LS, Koushiappas, Bullock, Kaplinghat 2007
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With substructure, fluxes may be ‘boosted’
LS, Koushiappas, Bullock, Kaplinghat 2007
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Conclusions and Outlook
• Proliferation of interesting dark matter models to constrainwith 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 hypothesisthat the present MW satellites reside in the most massivesubhalos
• New constraints for dark matter annihilations.
Louie Strigari UC Irvine