Transcript Testing Warm Dark Matter Model with Dwarf Galaxies

Dark Matter, Small-Scale Structure, and
Dwarf Galaxies
Louie Strigari
Center for Cosmology and
Particle Physics
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New York University
10.19.2007
Main Collaborators: James Bullock, Manoj Kaplinghat (UC Irvine)
Local Group circa 2003
Name
Year
Discovered
LMC
SMC
Sculptor
Fornax
Leo II
Leo I
Ursa Minor
Draco
Carina
Sextans
Sagittarius
1519
1519
1937
1938
1950
1950
1954
1954
1977
1990
1994
•Possible that up to 3x more exist at these luminosities [e.g. willman et al 2004]
•About a dozen satellites of M31
Louie Strigari, UC
Irvine
Local Group circa 2007
Name
Year
Discovered
LMC
SMC
Sculptor
Fornax
Leo II
Leo I
Ursa Minor
Draco
Carina
Sextans
Sagittarius
Ursa Major I
Willman I
Ursa Major II
Bootes
Canes Venatici I
Canes Venatici II
Coma
Segue I
Leo IV
Hercules
Leo T
Bootes II
Louie Strigari, UC
Irvine
1519
1519
1937
1938
1950
1950
1954
1954
1977
1990
1994
2005
2005
2006
2006
2006
2006
2006
2006
2006
2006
2007
2007
?
Questions to be addressed
• Is there a missing satellites problem is
CDM?
• What is the smallest dark matter system?
• Can we ever distinguish between cores
and cusps?
• Viable alternatives to CDM? What are
their phenomenological implications?
Louie Strigari, UC
Irvine
CDM: Cosmological Consequences
Zentner & Bullock 2003
Louie Strigari, UC
Irvine
CDM: Predictions including ``astrophysics”
We are seeing:
1) Earliest Forming
halos
2) Largest before
capture
3) Most massive today
4) Some combination
Bullock et al. 2001; Chiu, Gnedin,
Ostriker 2001; Somerville 200; Stoehr et
al. 2002; Hayashi et al. 2003; Kravtsov
et al. 2004; Gnedin & Kravtsov 2006;
Diemand et al. 2006
Louie Strigari, UC
Irvine
Kravtsov et al 2004
Maximum Circular Velocities?
Walker et al. ApJL 2007
Louie Strigari, UC
Irvine
Characteristic Mass of Satellites
Via Lactea
Error projections:
200 LOS stars
0.6 kpc appropriate scale to characterize well-known MW
satellites
Louie Strigari, UC
Irvine
Mass Constraints: Take I
The `Old’ Dwarfs
Likelihoods are marginalized
over 6-dimensional
parameter space defining the
dwarfs.
Very new data:
M0.6 ~ [2-7] x 106
Msun (Walker et al. 2007)
Largest mass galaxies
are least luminous and
least extended
Strigari, Bullock, Kaplinghat, Diemand, Kuhlen, Madau ApJ 2007
Louie Strigari, UC
Irvine
Implications: Take I
Strigari, Bullock, Kaplinghat, Diemand, Kuhlen, Madau ApJ 2007
Precise Mass function rules out most massive z=0 hypothesis
Louie Strigari, UC
Irvine
Belukurov et al 2006
Louie Strigari, UC
Irvine
Mass Constraints: Take II
The Old and the New
300 pc is better scale to
characterize the new
and old MW satellites
Mass within tidal radius of
Willman 1 ~ 2x the
estimate of Martin et al.
2007
Mass is independent of
halo luminosity (Mateo 1998)
Louie Strigari, UC
Irvine
Implications: Take II
Masses are similar, but the CDM mass function is
steep over the same range
Louie Strigari, UC
Irvine
CDM: Cosmological Consequences
cusp
core
Simon et al. 2005, Kuzio de Naray et al. 2006
Low mass dark matter halos are less `cuspy’ than predicted in CDM
Louie Strigari, UC
Irvine
Dwarf kinematics (Circa 2005)
Are survival of globular
clusters in Fornax a sign of
a kpc-sized core?
Gilmore et al 2007 find no- dSph requires the existence of central
cusps, and there is a characteristic dark matter core density
Louie Strigari, UC
Irvine
Strigari et al. 2006
Velocity Anisotropy
What can we learn from dwarfs?
Truth = core
Louie Strigari, UC
Irvine
Truth = cusp
Proper Motions

• Require accuracy on stellar
transverse velocities of 5 km/s
• At < 100 kpc, this
corresponds to accuracy 10
micro-arcseconds/yr
Louie Strigari, UC
Irvine
R
Astronomy = “star naming”
Astrometry = “star measuring”
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Reflex Motion of Sun
from 100pc (axes 100
µas)
SIM Positional
Error Circle
(4µas)
Hipparcos
Positional
Error Circle
(0.64 mas)
Adapted from:
http://planetquest.jpl.nasa.gov/SIM/sim_index.cfm
SIM PlanetQuest (Space Interferometry Mission)
Louie Strigari, UC
Irvine
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
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
Louie Strigari, UC
Irvine
Constraints with SIM
Strigari, Bullock, Kaplinghat ApJL 2007
Inner slope is never well-constrained. However, log-slope at several
hundred pc is constrained. This is sufficient to distinguish cores and
cusps.
Louie Strigari, UC
Irvine
Distinguishing Cores from Cusps
Strigari, Bullock, Kaplinghat ApJL 2007
SIM key project would entail 1000 hrs of observing time and
200 stars from multiple dSphs
Louie Strigari, UC
Irvine
Warm Dark Matter
Abazajian
2006
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Hogan & Dalcanton 2000
Seljak et al 2006, Viel et al 2006 find
mwdm > 14 keV
[Tremaine-Gunn Bound]
 m 4
3
3
Q  5 10 
 M sun pc (km /s)
keV 
4
Spergel & Steinhardt 2000, Ostriker and
Steinhardt 2003, Bode, Ostriker, & Turok 2001,
Cen 2000, Sanchez-Salcedo 2003
Louie Strigari, UC
Irvine
QCDM

 mcdm 3 / 2
3
3
 7 10 
 M sun pc (km/s)
100GeV 
14
Warm Dark Matter
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Ly-alpha + velocity dispersion imply small WDM cores
-Strigari et al ApJ 2006
Louie Strigari, UC
Irvine
Dark Matter from Early Decays
What if dark matter freezes-out, then
decays to a `superweakly’ interacting
particle? [Feng, Rajaraman, Takayama
2003]
Large velocity at production: 0.1-1c
Free-streaming scale: Q-1/3
Reduced Phase-Space Density
 103
6
Q  10 
m /m
DM

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3
3 z

decay
3
3

 M sun pc (km/s)
 
 1000 
See also Kang, Kawasaki, Steigman
1993; Starkman, Kaiser, Malaney 1994
Cembranos et al., Kaplinghat (2005)
Is dark matter from decays just a oneparameter family of models?
Louie Strigari, UC
Irvine
Dark Matter from Late Decays
Mass splitting is a free parameter:
what if they are of order GeV?
(Universal Extra Dimensions)
1014 sec.
Free-streaming scale now
depends on the lifetime: (Meta-CDM)
1012 sec.
Distinguishing between
cold and `warm’ dark
matter now requires
separate investigation of
dwarf galaxies and LSS
Neutrino WDM
Strigari, Kaplinghat, Bullock PRD 2006
Louie Strigari, UC
Irvine
The low energy gamma-ray background:
Are WIMPs stable?
G
Cembranos, Feng, Strigari, PRL 2007
MeV gamma-ray background unexplained by astrophysical sources
Louie Strigari, UC
Irvine
Dark matter, gamma-rays, 511 keV photons
Cembranos & Strigari
M ~ MeV
 ~ 1020/M(TeV)
Teegarden &
Watanabe
Picciotto & Pospelov 2005, Hooper &
Wang 2005, Kasuya & Kawasaki
2006, Finkbeiner & Weiner 2007,
Pospelov & Ritz 2007
Louie Strigari, UC
Irvine
Indirect Dark Matter Detection
Flux = Particle Physics x Astrophysics
Strigari, Koushiappas, Bullock, Kaplinghat PRD 2007
Louie Strigari, UC
Irvine
Indirect Dark Matter Detection
Boost factor
Strigari et al. PRD 2007
Louie Strigari, UC
Irvine
The most dark matter dominated galaxies:
Willman 1, Coma, Ursa Major II
These galaxies may be visible in gamma-rays with
GLAST
Dark substructure `boosts’ the fluxes
Louie Strigari, UC
Irvine