Louie Strigari - University of California, Irvinelstrigar/kicp.pdf · • Astronomy = “star...

Louie StrigariUC Irvine

Center for Cosmology

KICP, 5.18.2007

Determining the Nature of Dark Matter with Astrometry

Collaborators: James Bullock, Manoj Kaplinghat

Dark Matter in Cosmology

Standard

WIMP

‘Cold’

Proliferation of candidates

Astrophysical implications

Direct detection

Indirect detection

The `nature’ of dark matter

not hot

cold vs warm

Is ‘warm’ interesting?

Ωh2 = 0.113 ±0.009

Louie Strigari, UC Irvine KICP, 5.18.2007

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?

Astrophysical Constraints on Dark Matter


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’

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

CDM: Cosmological Consequences


Dark matter freezes out with non-negligible velocitiesFree streaming: Reduces the numberof small halos

• 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

‘Standard’ Warm Dark Matter


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 ofdwarf galaxies set bydark matter physics?

Warm Dark Matter: Cosmological Consequences


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?

Dark Matter and Small Scale Structure


[Crude List]

!

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?’

Feng, Rajaraman, Takayama 2003

Large velocity at production: 0.1-1c

Free-streaming scale: Q-1/3

Reduced Phase-Space Density

Dark Matter from Early Decays [SuperWIMPs]


Strigari, Kaplinghat, Bullock PRD 2006

1014 sec.

1012 sec.

Neutrino WDM

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)

Dark Matter from Late Decays


Are WIMPs Stable?

χ→γG

Cembranos, Feng, Strigari, arXiv:0704.1658


About a dozen satellites of M31

Possible that up to 3x more exist at these luminosities [e.g. willman et al 2004]

Census of Milky Way Satellites (Circa 2003)

Name Year DiscoveredLMC 1519SMC 1519Sculptor 1937Fornax 1938Leo II 1950Leo I 1950Ursa Minor 1954Draco 1954Carina 1977Sextans 1990Sagittarius 1994

Census of Milky Way Satellites (Circa 2007)

Name Year DiscoveredLMC 1519SMC 1519Sculptor 1937Fornax 1938Leo II 1950Leo I 1950Ursa Minor 1954Draco 1954Carina 1977Sextans 1990Sagittarius 1994Canis Major 2003Ursa Major I 2005Willman I 2005Ursa Major II 2006Bootes 2006Canes Venatici I 2006Canes Venatici II 2006Coma 2006Leo IV 2006Hercules 2006Leo T 2007


Belukurov et al 2006

Walker et al ApJ 2006

Kinematics of Milky Way Satellites


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

At least 5 parameters

Jeans equations:

• Cusps remain cusps even accounting for tidal interactions[Kazantzidis et al. 2004, Dehnen 2005]

• Is there no dark matter in dwarf galaxies? [Kroupa et al. 2005]

The Parameter Space


Observational Inputs

Wilkinson et al 2000Martin et al 2007

Willman I


Strigari et al. ApJ 2006

Fornax

Line-of-sight velocity dispersion


Truth = core Truth = cusp

Velo

city

Aniso

trop

yWhat can we learn from dwarfs?


R

ϕ• Require accuracy onstellar transversevelocities of 5 km/s

• At < 100 kpc, thiscorresponds to accuracy10 micro-arcseconds/yr

Transverse velocities of stars


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

Astrometry 101


Reflex Motion of Sunfrom 100pc (axes 100µas)

ParallacticDisplacementof GalacticCenter

Apparent GravitationalDisplacement of aDistant Star due toJupiter 1 degree away

SIM PositionalError Circle

(4µas)

.HipparcosPositionalError Circle(0.64 mas)

HST Positional ErrorCircle (~1.5 mas)

SIM PlanetQuest (Space Interferometry Mission)Ad

apte

d fr

om:

http

://p

lane

tque

st.jp

l.nas

a.go

v/SI

M/s

im_i

ndex

.cfm

• 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

Previous Considerations


Strigari, Bullock, Kaplinghat ApJL 2007

Constraints with SIM


Breaking the Degeneracy


Strigari, Bullock, Kaplinghat ApJL 2007

Goal: SIM key projectwould entail 1000 hrs ofobserving time

200 stars frommultiple dSphs

Optimizing Observations


What can we learn now?

Halo masses at about 600 pcare constrained to within 20%.Maximum circular velocitiesnot constrained.-Strigari, Bullock, Kaplinghat ApJL 2007


Strigari, Bullock, Kaplinghat, Diemand, Kuhlen, Madau 2007

Strigari, Bullock, Kaplinghat, Diemand, Kuhlen, Madau 2007

Earliest forming halos

Largest before accretion[Bullock et al 2000, Kravtsov et al2004, Gnedin & Kravtsov 2006,Moore et al 2006]

Redefining the Missing Satellites Problem


Dark subhalos

MW satellites

Mass function of new dwarfs


• New dwarfs willlikely spread a widerange of masses

• Not necessarily lessmassive than moreluminous dwarfs

Galactic center: astrophysical issues, backgrounds [e.g. Bergstrom,Ullio, Buckley 1999; Hooper & Dingus 2004; Profumo 2005]

Dark substructures [Tasitsiomi & Olinto 2003; Koushiappas, Zentner, &Walker 2003

Luminous satellites [Baltz et al. 2000; Tyler 2002; Evans, Ferrer, Sarkar2003, Bergstrom & Hooper 2005, Profumo & Kamionkowski 2006, Colafrancesco,Profumo, Ullio 2006]

Indirect Dark Matter Detection

Flux = Particle Physics x Astrophysics


LS, Koushiappas, Bullock, Kaplinghat PRD 2007

Constraints on Astrophysical Parameters


Two order ofmagnitude boost?

Fluxes are ‘boosted’ with substructure


LS, Koushiappas, Bullock, Kaplinghat PRD 2007

Boost factor

• 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

• Luminous satellites promising for dark matter annihilations.


Conclusions and Outlook

Louie Strigari - University of California, Irvinelstrigar/kicp.pdf · • Astronomy = “star...

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