Download - Where will supersymmetric dark matter first be seen? Liang Gao National observatories of China, CAS
Cold dark matter ?
UK DM search (Boulby mine)
Fermi
Dark matter discovery possible in several ways:
Evidence for SUSY
Annihilation radiation
Direct detection
Indirect CDM detection through annihilation radiation
Theoretical expectation requires knowing r(x)
Accurate high resolution N-body simulations of halo formation from CDM initial conditions
Supersymmetric particles annihilation lead to production of g-rays which may be observable by FERMI
Intensity of annihilation radiation at x depends on:
I(x) a ∫ r2(x) ‹sv› dV
cross-sectionhalo density at x
China, UK, Germany, Netherlands, Canada collaboration
The Phoenix programme of cluster halo simulations
Gao LiangAdrian Jenkins Julio Navarro Volker Springel, Carlos FrenkSimon White
Simulation overview
9 clusters (Ph-[A-I]) with masses great than 5e14 Msun randomly selected from the MS9 clusters have been simulated with 10^8 particles inside their R200. Per DM particles ~5e6 Msun/h , force resolution 320 pc/hThe PhA halo has been simulated with 4 different resolutions. The PhA-1 has 10^9 particles inside its viral radius. Mass resolution 5e-5 Msun/h, softenning=150pc/h
The Density Profile of Cold Dark Matter Halos
Halo density profiles are independent of halo mass & cosmological parameters There is no obvious density plateau or `core’ near the centre. (Navarro, Frenk & White ‘97)Dwarf galaxies
Galaxy clusters
More massive halos and halos that form earlier havehigher densities (bigger )d Log radius (kpc)
Log
dens
ity (
101
0 M
o k
pc3)
The density profile is fit by the NFW form to ~10-20%. In detail, the shape of the profile is slightly different.
Deviations from NFW
R [kpc]
(-rr N
FW)/
r NFW
Aq-A-3Aq-A-2
Aq-A-4
An improved fitting formula
Log radius (kpc)Log radius (kpc)
resi
dual
sLo
g de
nsity
A profile whose slope is a power-law of r fits all halos to <5%
(similar to stellar distribution in ellipticals - Einasto)
Navarro et al 04
Has extra param: a
Deviations from NFW & Einasto forms
NFW Einasto
Aquarius
Phoenix
Galactic and cluster halos deviate from NFW to ~10-20% and from Einasto to <~ 7%
(-rr N
FW)/
r NFW
(-rr Ei
sna)/
r Eina
s
Gao, Frenk, Jenkins, Springel & White ‘11
The structure of the cusp
Scatter in the inner slope
Aquarius
Phoenix
slop
eg
= d
log/rd
lnr
r/r-2
Asymptotic slope ≤1
Gao, Frenk, Jenkins, Springel & White ‘11
The subhalo mass function is shallower than M-2
The mass function of substructures
d N/ d
Msu
b [ M
o]
N(M) Ma
= -1.90a
Virgo consortium Springel et al 08
Msub [Mo]
Most of the substructure mass is in the few most massive halos The total mass in substructures converges well even for moderate resolution
300,000 subhalos within virialized region in Aq-A-1
Springel, Wang, Vogelsberger, Ludlow, Jenkins, Helmi, Navarro, Frenk & White ‘08
Aquarius
Virgo consortium Gao et al 2011
The specific mass function of substructures
Subhalo mass function steeper for galaxies than clusters
clusters: N(>m)~M0.97 galaxies: N(>m)~M0.90
Aquarius
Phoenix
msub/M200
N(m
sub)/
M2
00
~20% more subs per unit mass in clusters
The cold dark matter linear power spectrum
k [h Mpc-1]Large scales
Fluc
tuati
on a
mpl
itude
k3 P(k)z~1000
Small scales
n=1
CMB
Superclusters
Clusters
Galaxies
10-6 Mo for 100 GeV wimp
lcut α mx-1
Substructures
Important for annhilation radiation
Intensity a ∫ r2(x) ‹sv› dV
Need to extrapolate to Earth mass gravitational physics
Extrapolation to Earth mass
Annihilation luminosity of subhalos
Extrapolate using halo mass function (x1.5) + mass-concentration reln
Annihilation luminosity of subs. per unit mass
Gao, Frenk, Jenkins, Springel & White ‘11
Subhalo L (per halo mass) similar to L of field halo mass fn.
field halo mass function
Aquarius
Phoenix
R [kpc]
Su
rfa
ce b
righ
tne
ss
Annihilation radiation from cluster halos
Smooth main halo
Resolved substructures M<5x107 Mo
Substructures M>10-12 Mo
Substructures M>10-6 Mo
Gao, Frenk, Jenkins, Springel & White ‘11
Substructure boost
For dwarf galaxy b~few For galactic halos b=97 For cluster halos b~1300 (Gao et al. ‘11)
Extrapolating luminosity down to 10-6Mo (e.g. for 100 Gev WIMP)
Annihilation radiation
Su
rfa
ce b
righ
tne
ss
R [arcmin]
Coma cluster
UMII dwarf
M31 galaxy
Surface brightness
Gao, Frenk, Jenkins, Springel & White ‘11
Annihilation radiation
sig
nal
-to-
nois
e
R [arcmin]
Coma cluster
UMII dwarf
M31 galaxy
Signal-to-noise
Gao, Frenk, Jenkins, Springel & White ‘11
Conclusions
Halos have nearly universal “cuspy" density profiles
~10% of halo mass is in substructures, primarily in outer parts
Emission from galaxies and clusters is extendedboost factor is about one thousand for clusters, one hundred for galaxy and few for dwarfs
Coma cluster has 10 × (S/N) of UMAII, thus offer the bestplace to detect dark matter annihilation
Annihilation radiation