Where will supersymmetric dark matter first be seen? Liang Gao National observatories of China, CAS

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

Dwarf galaxies around the Milky WayFe

rmi

Fornax

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

z = 0.0

Pho

enix

clu

ster

hal

os

The main halo and the substructures all contribute to the annihilation radiation

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)

Orignal NFW simulations resolved down to 5% of rvir

Density profile r(r)

z=0

NFW

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 cuspsl

ope

slop

e

Aquarius Phoenix

NFW

The structure of the cusp

Scatter in the inner slope

Aquarius

Phoenix

slop

eg

= d

log/rd

lnr

r/r-2

Asymptotic slope ≤1


Cluster dark halos seem to have cusps

Substructures

Important for annhilation radiation

Intensity a ∫ r2(x) ‹sv› dV

Large number of substructures survive, mostly in outer parts

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

Large number of substructures survive, mostly in outer parts

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


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


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)


Su

rfa

ce b

righ

tne

ss

R [arcmin]

Coma cluster

UMII dwarf

M31 galaxy

Surface brightness



sig

nal

-to-

nois

e

R [arcmin]

Coma cluster

UMII dwarf

M31 galaxy

Signal-to-noise


Properties of nearby galaxy clusters, satellites of the Milky Way and M31

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


Documents

Where will supersymmetric dark matter first be seen? Liang Gao National observatories of China, CAS