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  (x)  Accurate high resolution N-body simulations of halo formation from CDM initial conditions Supersymmetric particles annihilation lead to production of  -rays which may be observable by FERMI Intensity of annihilation radiation at x depends on: I(x)  ∫  2 (x) ‹  v› dV cross-section halo density at x

Dwarf galaxies around the Milky Way Fermi Fornax

China, UK, Germany, Netherlands, Canada collaboration The Phoenix programme of cluster halo simulations Gao Liang Adrian Jenkins Julio Navarro Volker Springel, Carlos Frenk Simon White

Simulation overview 9 clusters (Ph-[A-I]) with masses great than 5e14 Msun randomly selected from the MS 9 clusters have been simulated with 10^8 particles inside their R200. Per DM particles ~5e6 Msun/h, force resolution 320 pc/h The 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

Phoenix cluster halos

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 have higher densities (bigger  Log radius (kpc) Log density (10 10 M o kpc 3 )

Orignal NFW simulations resolved down to 5% of r vir Density profile  (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]  NFW )/  NFW Aq-A-3 Aq-A-2 Aq-A-4

An improved fitting formula Log radius (kpc) residuals Log density 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: 

Deviations from NFW & Einasto forms NFW Einasto Aquarius Phoenix Galactic and cluster halos deviate from NFW to ~10-20% and from Einasto to <~ 7%  NFW )/  NFW  Eisna )/  Einas Gao, Frenk, Jenkins, Springel & White ‘11

The structure of the cusp slope Aquarius Phoenix NFW

The structure of the cusp Scatter in the inner slope Aquarius Phoenix slope  = dlog  dlnr r/r -2 Asymptotic slope ≤1 Gao, Frenk, Jenkins, Springel & White ‘11

Cluster dark halos seem to have cusps

Substructures Important for annhilation radiation Intensity  ∫  2 (x) ‹  v› dV

Large number of substructures survive, mostly in outer parts

The subhalo mass function is shallower than M -2 The mass function of substructures dN/dM sub [ M o ] N(M)  M   Virgo consortium Springel et al 08 M sub [M o ] 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)~M 0.97 galaxies: N(>m)~M 0.90 Aquariu s Phoenix m sub /M 200 N(m sub )/M 200 ~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 Fluctuation amplitude k 3 P(k) z~1000 Small scales n=1 CMB Superclusters Clusters Galaxies M o for 100 GeV wimp cut α m x -1

Substructures Important for annhilation radiation Intensity  ∫  2 (x) ‹  v› 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 Aquariu s Phoenix

R [kpc] Surface brightness Annihilation radiation from cluster halos Smooth main halo Resolved substructures M<5x10 7 M o Substructures M> M o Substructures M>10 -6 M o 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 M o (e.g. for 100 Gev WIMP)

Annihilation radiation Surface brightness R [arcmin] Coma cluster UMII dwarf M31 galaxy Surface brightness Gao, Frenk, Jenkins, Springel & White ‘11

Annihilation radiation signal-to-noise R [arcmin] Coma cluster UMII dwarf M31 galaxy Signal-to-noise Gao, Frenk, Jenkins, Springel & White ‘11

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 extended boost 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 best place to detect dark matter annihilation Annihilation radiation