Radio signals from galactic and extragalactic dark matter

Radio signals from galactic and extragalactic dark matter Nicolao Fornengo Department of Theoretical Physics, University of Torino and Istituto Nazionale di Fisica Nucleare (INFN) Torino Italy fornengo@to.infn.it nicolao.fornengo@unito.it www.to.infn.it/~fornengo www.astroparticle.to.infn.it Torino CETUP* 2012 Workshop Deadwood/Lead, SD (USA) 16.07.2012

Astrophysical dark matter signals Direct detection Cosmic Antiprotons Electrons/Positrons Antideuterons Neutrinos from the Earth, Sun from the Milky Way Gamma rays galactic emission extragalactic emission Radio waves galactic emission extragalactic/cosmological emission Effects on the CMB recombination altered by early time particle injection from DM Sunyaev-Zeldovic effect in galaxy clusters

Radio signals from dark matter DM annihilation/decay into e+/e- produce radio signals by synchrotron emission in galactic/extragalactic magnetic fields Emission in the MHz-GHz frequency range occurs for: Electrons/positrons energies in the GeV-TeV range (*) Magnetic fields of the order of microg q E 15 GHz /B µg GeV (*) Relevant interval for WIMP DM in the GeV-TeV mass range More specifically: electron energies < 10 GeV produce signals at frequencies < GHz

Targets Galactic Center Good target for spiky DM profile On the scale of the bulge: WMAP haze? GC is avery active region: desentanglement of a signal rather complicated Galactic Halo Mid/high latitudes may be cleaner Low radio frequences for soft e+/e- spectra, microwave range otherwise Extragalactic diffuse emission ARCADE 2: isotropic radio emission significantly brighter than expected: requires a new population of unresolved sources which become the most numerous at very low (observationally unreached) brightness [maybe DM?] Anisotropies studies may be a goal for the future Extragalactic objects Non-thermal emission with spherical morphology correlated with the DM halo profile inferred from kinematic measurements in the external part of extragalactic objects can be a strong evidence for WIMP induced emission Most promising targets: dwarf spheroidal galaxies and clusters of galaxies

Based on: NF, Lineros, Regis, Taoso, Phys.Rev.Lett. 107 (2011) 271302 [arxiv: 1108.0569] NF, Lineros, Regis, Taoso, JCAP 01(2012)005 [arxiv:1110.4337] NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Galactic radio signal

Synchrotron emissivity Synchrotron flux: j (x) = Z de n e (E,x) dw d (x) Electron number density: n e (E,x) Emission power: dw d (,B?)= p 3 e 3 B? m e c 2 F c,? B? : perp component of B ~ c,? = 3eB?E 2 4 m 3 ec 5 F (x) =x Z 1 x d K 5/3 ( )

Electron number density Source term q(x,e)= 1 2 (x) 2 ( v) M DM dn de (E) Electron/positron propagation K 0 E r 2 @ @E b(e) = q(x,e) Diffusion: L z [kpc] K 0 kpc 2 /Myr MIN 1 0.0016 0.85 MED 4 0.0112 0.70 MAX 15 0.0765 0.46 Energy losses: b(e) =b ISRF (E)+b synch (E,B) b ISRF (E) : Compton scattering on ISRF b synch (E,B)= 4e4 B 2 9m 4 c 7 E2 disk diffusive halo dark matter halo R g Lz

Magnetic field r r B(r, z) =B 0 exp R m z L m GMF Model Parameters L m [kpc] R m [kpc] I L z R g II L z R g III 1 R g IV constant

Morphology of radio sky at 45 MHz observed NFW MED propag params NFW MIN propag params NF, Lineros, Regis, Taoso, JCAP 01 (2012) 005 [arxiv:1110.4337] NFW MAX propag params 10 GeV DM Annihilation into muon with thermal cross section Exp decaying B(r,z) with B TOT = 10 microg

Sky temperature at the galactic poles NFW MED propag params 10 9 10 8 B 0 = 6 µg GSM North pole GSM South pole Surveys North pole Surveys South pole Fornengo, Lineros, Regis, Taoso (2011) Exp decaying B(r,z) with B TOT = 10 microg T [K] (ν/mhz) 2.5 10 7 10 6 10 5 300 MeV 1 GeV 3 GeV 10 GeV 10 4 10 3 µ + µ channel bb channel M DM = 10 GeV M DM = 100 GeV 1 2 3 4 log 10 (ν/mhz) NF, Lineros, Regis, Taoso, JCAP 01 (2012) 005 [arxiv:1110.4337]

Galactic radio signal Fornengo, Lineros, Regis, Taoso (2011) 45 MHz Data: l < 3 DM models: l = 0 T [K] (ν/mhz) 2.5 10 9 10 8 10 7 M DM =10 GeV MED GMF model I 45 MHz µ + µ bb τ + τ e + e NFW Isothermal 10 6 80 60 40 20 0 20 40 60 80 Galactic latitude [degrees] Fornengo, Lineros, Regis, Taoso (2011) 10 9 M DM =10 GeV µ + µ GMF model I 45 MHz MIN MED MAX NFW Isothermal T [K] (ν/mhz) 2.5 10 8 10 7 10 6 80 60 40 20 0 20 40 60 80 Galactic latitude [degrees] NF, Lineros, Regis, Taoso, JCAP 01 (2012) 005 [arxiv:1110.4337]

Skymaps 22 MHz 45 MHz 408 MHz 820 MHz 1420 MHz NF, Lineros, Regis, Taoso, JCAP 01 (2012) 005 [arxiv:1110.4337]

Galactic radio signal: bounds Bounds from combination of all frequency-skymaps T DM apple T obs +3 σv [cm 3 /s] 10 22 10 23 10 24 bb MIN MED MAX GMF model I NFW Isothermal hadronic channel (bb) Fornengo, Lineros, Regis, Taoso (2011) 10 25 σv [cm 3 /s] 10 26 Conservative bounds: - no astrophysical background subtraction - no DM substructures included [MHz] Survey rms noise [K] 22 DRAO 5000 45 Guzman et al. 3500 408 Haslam et al. 0.8 820 Dwingeloo 1.4 1420 Stockert 0.02 10 22 10 23 10 24 10 25 10 26 10 27 10 1 10 2 10 3 M DM [GeV] e + e GMF model I MIN MED MAX NFW Isothermal 10 28 10 0 10 1 10 2 10 3 M DM [GeV] Bounds from all sky leptonic channel (ee) Fornengo, Lineros, Regis, Taoso (2011) Bounds from all sky NF, Lineros, Regis, Taoso, JCAP 01 (2012) 005 [arxiv:1110.4337]

Galactic radio signal: bounds Bounds from combination of all frequency-skymaps T DM apple T obs +3 σv [cm 3 /s] 10 22 10 23 10 24 10 25 µ + µ GMF model I MIN MED MAX NFW Isothermal Fornengo, Lineros, Regis, Taoso (2011) 10 26 10 27 10 28 10 0 10 1 10 2 10 3 M DM [GeV] Bounds from all sky Fornengo, Lineros, Regis, Taoso (2011) σv [cm 3 /s] 10 22 10 23 10 24 10 25 µ + µ GMF model I Cut b >15 degrees MIN MED MAX NFW Isothermal 10 26 10 27 Bounds excluding GC region 10 28 10 0 10 1 10 2 10 3 M DM [GeV] NF, Lineros, Regis, Taoso, JCAP 01 (2012) 005 [arxiv:1110.4337]

Galactic radio signal: bounds [MHz] Survey rms noise [K] 22 DRAO 5000 45 Guzman et al. 3500 408 Haslam et al. 0.8 820 Dwingeloo 1.4 1420 Stockert 0.02 Fornengo, Lineros, Regis, Taoso (2011) σv [cm 3 /s] 10 21 10 22 10 23 10 24 10 25 10 26 22 Mhz 45 Mhz 408 Mhz 820 Mhz 1420 Mhz µ + µ NFW MED GMF model I 10 27 10 28 All-sky bounds from individual frequencies 10 0 10 1 10 2 10 3 M DM [GeV] NF, Lineros, Regis, Taoso, JCAP 01 (2012) 005 [arxiv:1110.4337]

Cosmological radio signal

Radio observables Radio emission may occurr also in extragalactic halos Three relevant observables: Intensity of the emission Ø High frequency: CMB largely dominates Ø Close and below 1 GHz: CMB may be efficiently subtracted Ø Low frequencies: extra-galactic sources dominate Differential number counts of sources Ø Quite useful to study different radio populations Ø Dominated by radio-loud AGNs down to the mjy level Ø Star-forming galaxies and radio-quiet AGN take over at fainter fluxes Angular correlations Ø Angular distribution of sources is a powerful probe of LS clustering Ø Wide-area radio surveys allow to test large scales Ø 2-point correlation function and angular power spectrum

Key elements: Dark matter radio signals Halo mass function and concentration DM distribution in halos Cosmological evolution e+/e- propagation and energy losses Magnetic fields DM benchmarks Name Mass ( a v)[cm 3 s 1 ] [s] Dominant [GeV] annihilating case decaying case final state B1 100 3 10 26 4 10 28 b b B2 10 3 10 26 5 10 27 µ + µ

Total intensity 10 6 Radio 10-5 Gamma-rays 2 T [GHz 2 K] 10 5 10 4 10 3 10 2 10 1 10 0 10-1 10-2 10-3 CMB Best-fit power-law of the excess decaying B1 decaying B2 annihilating B1 annihilating B2 AGN 10-4 10-2 10-1 10 0 10 1 10 2 10 3 10 4 [GHz] SFG E 2 dn/de [GeV cm -2 s -1 sr -1 ] 10-6 10-7 10-8 10-9 10-10 CHANDRA IC COMPTEL FERMI FSR 10-11 10-6 10-5 10-4 10-3 10-2 10-1 10 0 10 1 10 2 E [GeV] 0 Radio is more constraining than gamma-rays for DM producing leptons For DM producing hadrons, contstraining power is similar NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Source number counts 10 5 Benchmark B2 10 2 c S 5/2 dn/ds [Jy 3/2 sr -1 ] 10 4 10 3 10 2 10 1 10 0 10-1 10-2 325 MHz, c=10 1.4 GHz, c=1 4.8 GHz, c=0.1 AGN SFG DM 10-3 -9-8 -7-6 -5-4 -3-2 -1 0 1 2 Log( S[Jy] ) S 5/2 dn/ds [Jy 3/2 sr -1 ] 10 1 10 0 10-1 10-2 10-3 1.4 GHz annihilating B1 annihilating B2 decaying B1 decaying B2 10-4 -9-8 -7-6 -5-4 -3-2 Log( S[Jy] ) DM constribution becomes more dominant for sub-microjy levels Decaying-DM spectrum steeper -> takes over at even smaller fluxes Annihilating DM(density) 2 + (growing of concentration at small halo masses): makes the smaller and fainter structures more important than brighter halos NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Differential number counts 10 7 10 6 10 5 DM ann DM dec Benchmark B2 Faint sources 0.1 µjy < S < 1 µjy dn/dz [deg -2 ] 10 4 10 3 10 2 10 1 SFG S > 3 mjy 1.4 GHz AGN 10 0 DM ann DM dec Bright sources 10-1 10-2 0.1 1 redshift z DM-induced radio emission is mostly produced at low-redshifts NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Angular correlation l (l+1) C l /(2 ) 10-2 10-3 10-4 10-5 10-1 10-2 10-3 10-4 10-5 10-6 1.4 GHz S < 1 µjy DM 1.4 GHz S > 10 mjy NVSS SFG Faint sources DM AGN Bright sources 10 100 1000 Multipole l Benchmark B2 l (l+1) C l /(2 ) [mk 2 ] l (l+1) C l /(2 ) [µk 2 ] 10 8 10 7 10 6 10 5 10 4 10 3 10 2 10 2 10 0 10-2 10-4 10-6 408 MHz AGN+SFG DM ann 150 GHz DM ann from Haslam et al. map DM dec AGN+SFG All brightnesses SPT DM dec 10 100 1000 10000 Multipole l Bright sources: 1-halo term dominates, follows Poisson noise; astro sources dominate Faint sources: 2-halo term dominates; DM dominates at low multipoles NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Effect of clustering 10 3 Benchmark B1 10 2 10 2 10 1 1.4 GHz NFW, M cut =10 6 M sun 2 T [GHz 2 K] 10 1 10 0 10-1 10-2 10-3 10-4 10-5 cvir1 cvir2 M cut =10 6 M sun NFW Burkert Moore M cut =10-6 M sun S 5/2 dn/ds [Jy 3/2 sr -1 ] 10 0 10-1 10-2 10-3 10-4 10-5 NFW, M cut =10-6 M sun Burkert, M cut =10 6 M sun Moore, M cut =10-6 M sun 10-6 10-2 10-1 10 0 10 1 10 2 10 3 10 4 [GHz] 10-6 -12-11 -10-9 -8-7 -6-5 -4-3 Log( S[Jy] ) Main uncertainty comes from extrapolation al low masses Uncertainty in clustering (without considering here subcstructures) reaches 2 odm NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Effect of clustering 10 0 10-1 NFW, M cut =10 6 M sun Moore, M cut =10 6 M sun Benchmark B1 1.4 GHz S < 1 mjy l (l+1) C l / (2 ) 10-2 10-3 10-4 10-5 Burkert, M cut =10 6 M sun NFW, M cut =10-6 M sun 1h-term 2h-term 10-6 10-7 10-8 10 100 1000 10000 Multipole l NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Effect of substructures 10 3 Benchmark B1 10 2 2 T [GHz 2 K] 10 2 10 1 10 0 10-1 10-2 10-3 10-4 10-5 no subhalo s M cut =10 6 M sun s M cut =10-6 M sun 10-6 10-2 10-1 10 0 10 1 10 2 10 3 10 4 [GHz] S 5/2 dn/ds [Jy 3/2 sr -1 ] 10 1 10 0 10-1 10-2 10-3 10-4 1.4 GHz subhalos resolved subhalos unresolved no subhalo s M cut =10 6 M sun s M cut =10-6 M sun 10-5 -9-8 -7-6 -5-4 -3 Log( S[Jy] ) NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Effect of substructures l (l+1) C l / (2 ) [erg cm -2 s -1 sr -1 ] 2 10-20 10-21 10-22 10-23 10-24 10-25 10-26 10-27 10-28 10-29 10-30 10-31 C l from host halo Benchmark B1 1.4 GHz s C l from subhalo (M cut =10 6 M sun, biased) s C l from subhalo (M cut =10-6 M sun, biased) C l from subhalo (M cut =10-6 M sun, anti-biased) S < 1 mjy 1h-term 2h-term 10-32 10 100 1000 10000 Multipole l NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

2 T [GHz 2 K] 10 3 10 2 10 1 10 0 10-1 10-2 10-3 10-4 10-5 (1) (2) B = B 0 = 10 µg B = B 0 ( M / M max ) 0.1, B 0 = 10 µg B = B 0 exp( -r / (R vir /50) ), B 0 = 10 µg B = B 0 = 1 µg 10-6 10-2 10-1 10 0 10 1 10 2 [GHz] Effect of magnetic field Benchmark B2 NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517] 10-5 -9-8 -7-6 -5-4 -3-2 -1 Log( S[Jy] ) S 5/5 dn/ds [Jy 3/2 sr -1 ] 10 1 10 0 10-1 10-2 10-3 10-4 1.4 GHz B = B 0 = 10 µg B = B 0 ( M / M max ) 0.1, B 0 = 10 µg B = B 0 exp( -r / (R vir /50) ), B 0 = 10 µg The bulk of the DM signal comes from low redshift: z-dep for B not critical Scaling with mass of objects may be more critical case (1): emission suppression is small objects -> depletion is number counts at small S case (2): emission suppression in large objects

Effect of magnetic field 10-25 Benchmark B2 1.4 GHz 0.1 µjy < S < 1 µjy l (l+1) C l / (2 ) [erg cm -2 s -1 sr -1 ] 2 10-26 10-27 10-28 10-29 10-30 10-31 10-32 1h-term 2h-term B = B 0 = 10 µg B = B 0 ( M / M max ) 0.1, B 0 = 10 µg B = B 0 exp( -r / (R vir /50) ), B 0 = 10 µg 10-33 10 1 10 2 10 3 10 4 Multipole l NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Constraints on DM properties Annihilation rate v [cm 3 s -1 ] 10-21 10-22 10-23 10-24 10-25 µ + µ Annihilating dark matter Intensity Counts Angular Annihilation rate v [cm 3 s -1 ] 10-20 10-21 10-22 10-23 10-24 10-25 MAX MIN µ + µ b - b _ 10-26 10 100 1000 WIMP mass M [GeV] 10-26 10 1 10 2 10 3 WIMP mass M [GeV] Future survey are expected to improve considerably the bounds from number counts and anisotropies NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

Constraints on DM properties 10-22 10-23 MAX MIN Decaying dark matter Decay rate -1 [s -1 ] 10-24 10-25 10-26 10-27 µ + µ b - b _ 10-28 10 100 1000 WIMP mass M [GeV] NF, Lineros, Regis, Taoso, JCAP 03 (2012) 033 [arxiv:1112.4517]

ARCADE excess After subtraction of an isotropic component, ARCADE reports a remaining flux (interpreted as extragalactic) 5 6 times larger than the total contribution from detected extragalactic radio sources ARCADE: Singal et al., Astrophys. J. 730 (2011) 138 A. Kogut et al., Astrophys. J. 734 (2011) 4 Extrapolating the source number counts to lower (unreached) brightness, the excess remains Systematics effects and galactic sources seems excluded Such a level of radio extragactic emission does not appear to have an immediate explanation in terms of standard astrophysical scenarios,, expecially when multiwavelength constraints are applied 10-2 10-1 10 0 10 1 10 2 [GHz] T [K] 10 5 10 4 10 3 10 2 10 1 10 0 10-1 CMB v=3 10-26 cm 3 /s, NFW B = 10 µg, b.f. sub =7 Sources contrib. from number counts µ + µ, M DM =10 GeV _ b - b, M DM =100 GeV, b.f.=20 Best-fit power-law of the excess NF, Lineros, Regis, Taoso, PRL 107 (2011) 27 27 [arxiv:1108.0569] DM can easily explain the excess without special fine tunings (Slight) preference for light (around 10 GeV) and leptophilic DM Nicolao Fornengo, University of Torino and INFN-Torino (Italy) CETUP* 2012 - Deadwood/Lead, SD - 16.07.2012

ARCADE excess Astrophysical galactic origin: appears to be rather unlikely Free free emission has been excluded based on the spectral shape Diffuse Galactic synchrotron foreground is estimated using two different methods (a cosecant dependence on Galactic latitude and the correlation between radio and atomic line emissions) A new population of numerous and faint radio sources (able to dominate source counts around μjy flux) has to be introduced Ordinary star forming galaxies with a radio to far infrared flux ratio which increases significantly with redshift can in principle offer a solution: this possibility is strongly constrained by multi wavelength observations The radio to far infrared emission has to be increased by a factor of 5 above what is observed in local galaxies, while current measurements show very mild evolution Radiative emission of secondary electrons in star forming galaxies would overproduce the gamma ray background from pion decays The same is true also for primary electrons unless such putative galaxies have extremely low gas density (and, in turn, low ratio of primary electrons to pions) or extremely efficient proton escape Nicolao Fornengo, University of Torino and INFN-Torino (Italy) CETUP* 2012 - Deadwood/Lead, SD - 16.07.2012

ARCADE excess corresponding multiwavelength signals COMPTEL 10 4 differential number counts 1.4 GHz 10-6 CHANDRA FERMI 10 3 E 2 dn/de [GeV cm -2 s -1 sr -1 ] 10-7 10-8 IC 0 FSR S 5/2 dn/ds [Jy 3/2 sr -1 ] 10 2 10 1 10 0 unresolved substructures resolved substructures 10-9 10-6 10-5 10-4 10-3 10-2 10-1 10 0 10 1 10 2 E [GeV] 10-1 AGN GAL DM 10-2 -9-8 -7-6 -5-4 -3-2 -1 0 1 2 Log( S[Jy] ) NF, Lineros, Regis, Taoso, PRL 107 (2011) 27 [arxiv:1108.0569] See also: Hooper et al., arxiv:1203.3547 Nicolao Fornengo, University of Torino and INFN-Torino (Italy) CETUP* 2012 - Deadwood/Lead, SD - 16.07.2012

Conclusions Radio emission in the MHz-GHz frequency range may be produced by DM annihilation/decay in our Galaxy or in the extragalactic environment Radio signals already pose bounds on WIMP DM comparable to other indirect detection searches: Galactic radio emission close to thermal annihilation for light DM Low-frequency surveys quite competivitve for light DM Potential channels of discovery (but require increased sensitivities): Source number counts at low brightnesses (below microjy) Angular correlations at low multipoles and low brightnesses Various sources of uncertainty are present: DM matter distribution (in the Galaxy / cosmological) Electron/positron propagation and energy losses Magnetic fields (galactic / extragalactic) Promising future with the development of many new, high-sensitivty detectors: ASKAP, EVLA, MeerKAT, LOFAR, SKA Nicolao Fornengo, University of Torino and INFN-Torino (Italy) CETUP* 2012 - Deadwood/Lead, SD - 16.07.2012