Transcript Testing Warm Dark Matter Model with Dwarf Galaxies

Measuring Dark Matter Properties
with Astrometry
Louie Strigari
TASC 2006
10/20/2006
In collaboration with: James Bullock, Manoj Kaplinghat, Stelios
Kazantzidis, Steve Majewski
Dark Matter and Galaxy Central Densities
CDM
QCDM
3/2


m
 7 1014  cdm  M sun pc3 (km/s)3
100GeV 
WDM

4
4  m 
3
3
Q  5 10 
 M sun pc (km /s)
keV 

cusp
Simon et al 05
core
SuperWIMPS & Meta-CDM
 103
6
Q  10 
m /m
DM

Louie Strigari
3
3 z

decay
3
3

 M sun pc (km /s)
 
 1000
UC Irvine
Dwarf Spheroidal Galaxies
To observer
Walker et al. 2006
 Exhibit no rotation
 DM dominated
 Information on DM halo from line of sight velocities
2

(r)r
2
R 2 stars (r) r,dm
2
 LOS 
dr

1  2 
2
2
I(R) 
r 
R r
Line of sight profiles
Strigari et al. 2006
Degeneracy with cores and cusps in all systems
Nothing prevents dark halos from being very extended
Projections
Degeneracy remains unbroken even with 10,000 stars
Space Interferometry Mission (SIM): extragalactic
astrometry with micro-arcsec resolution
http://planetquest.jpl.nasa.gov/SIM/sim_index.cfm
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Errors of order km/s on a few hundred stars at a
typical dSph distance
Louie Strigari
UC Irvine
Adapted from:
http://planetquest.jpl.nasa.gov/SIM/sim_index.cfm
How Precise is SIM?
Reflex Motion of Sun
from 100pc (axes 100
µas)
SIM Positional
Error Circle
(4µas)
Hipparcos
Positional
Error Circle
(0.64 mas)
HST Positional Error
Circle (~1.5 mas)
.
Parallactic
Displacement
of Galactic
Center
Apparent Gravitational
Displacement of a
Distant Star due to
Jupiter 1 degree away
Constructing moments for proper motions
= velocity anisotropy of the stars
Dark matter
2
 LOS
2

(r)r
2
R 2 stars (r) r,dm

dr

1  2 
2
2
I(R) 
r 
R r
2
2 


(r)

2
R
stars
r,dm (r)r
 R2 
1



dr


2 
2
2
I(R) 
r 
R r
2
2
 
I(R)
 1  
2
stars (r) r,dm
(r)r
R r
2
2
dr

R
Error estimates
2(n  2) 2
 
 theory
2
n
2
2nd
moment

4th
moment
n = number of
stars in sample
Reconstructing the central slope I.
(NFW)
Line of Sight
Proper motions
+
=
+
Reconstructing the central slope II.
(Cores)
Line of Sight
Proper motions
+
=
+