Dongsu Ryu (Chungnam National U, Korea)

Shock Waves in the Large Scale Structure of the Universe and Cosmic Rays Accelerated
Dongsu Ryu (Chungnam National U, Korea) Hyesung Kang (Pusan National U, Korea) cosmic rays: observations and theory a possible origin of cosmic rays in large scale structure: cosmological shocks waves in an adiabatic simulation effects of detailed physics (cooling/heating, feedback) May 17-19, th Korean Astrophysics Workshop KASI, Korea

May 17-19, 2006 4th Korean Astrophysics Workshop KASI, Korea
12 orders of magnitude 32 orders of magnitude direct measurements air shower E-2.7 E-3.1 extragalactic origin CRs observed at Earth particle energy spectrum power-law spectrum knee energy: 1015 eV ankle energy: eV N(E) ~ E-2.7 below the knee and steeper above E: up to ~1021 eV “universal” acceleration mechanism working on a wide range of scales → shock acceleration UHECRs: above the ankle May 17-19, th Korean Astrophysics Workshop KASI, Korea

Extra Galactic? Galactic? C,O,… GZK cutoff He Fe p knee 2 knee 1 ankle E-2.7 extra-Galactic component Galactic component May 17-19, th Korean Astrophysics Workshop KASI, Korea Nagano & Watson 00

Observational evidences for CRs in large scale structure
- diffuse radio halos and relics in over 30 clusters radio synchrotron (CR electrons + magnetic field) (Govoni, Feretti, Giovannini) - hard X-ray & EUV (?) emission in excess of thermal radiation inverse Compton scattering of CBR by CR electrons (Fusco-Feminao, Colafrancesco, Blasi, Lieu, Sarazin) - g-rays yet to be observed CR p + p → po decay → GeV g-ray CBR photons inverse Compton e- up to g-ray pp po g-ray CR protons Pion decay gamma May 17-19, th Korean Astrophysics Workshop KASI, Korea

diffuse raiod sources in clusters of galaxies prove the existence of relativistic electrons of energy  GeV and of magnetic fields  G on scales of Mpcs !! Coma cluster X-ray: ROSAT (White et al. 1993) thermal: X-ray 500 kpc RADIO: WSRT, 90 cm (Feretti et al.1998) nonthermal: radio May 17-19, th Korean Astrophysics Workshop KASI, Korea

A 2319: 1.4 Mpc CR e’s & magnetic fields COMA: 1.1 Mpc A 2255: 1.2 Mpc CL : 1.1 Mpc z = A 2163: 2.9 Mpc May 17-19, th Korean Astrophysics Workshop KASI, Korea

radio arcs in A3376 (Bagchi 2003)
observational evidence for accretion shocks or merger shocks ? 2.6 h50 -1 Mpc May 17-19, th Korean Astrophysics Workshop KASI, Korea

nonthermal hard X-ray emission from clusters
possible detections of hard X-ray excesses from clusters with BeppoSAX & RXTE Coma, A2319, A2256, … CR e’s Coma HXR BeppoSAX (Fusco-Femiano et al.) May 17-19, th Korean Astrophysics Workshop KASI, Korea

Why do we care about the CRs? - CRs are ubiquitous in astrophysical plasma. heliosphere (solar system) solar wind, interplanetary shocks - ISM of our Galaxy ECR ~ EB ~ Egas ~ ECMBR ~ erg/cm3 dynamically important in the ISM of galaxies sources: SNRs, stellar wind (OB stars), pulsars - ICM inside clusters of galaxies (and large scale structure) ECR,e ~ 0.01 Ethermal , ECR,p ~ Etheremal , EB ~ Ekinetic ~ 0.1 Ethermal sources: AGNs, galactic winds, turbulence, structure shocks May 17-19, th Korean Astrophysics Workshop KASI, Korea

Origins of cosmic rays in large scale structures
* cosmological shock waves - fresh injection/acceleration of protons and electrons (diffusive shock acceleration (DSA): Fermi first order process) - re-acceleration of CR electrons and protons (pre-existing or ejected by radio galaxies and etc …) (in relic radio ghosts) secondary electrons generated by CR protons + ICM (CR p + p → p + p + p, p± → m± → e± & po → g-rays ) * stochastic acceleration by the ICM turbulence * AGNs, galatic winds, and etc May 17-19, th Korean Astrophysics Workshop KASI, Korea

“Hillas Plot” for Emax = Z ba B R B R = Emax /(Z ba ) = 1020 eV
some plausible accelerators (after Hillas 1984) confinement and acceleration: Emax = Z ba B R B Emax: highest possible energy Z: charge of the CR particle Va/c = ba : speed of accelerator B: magnetic field strength R: size of accelerator B R = Emax /(Z ba ) = 1020 eV R May 17-19, th Korean Astrophysics Workshop KASI, Korea

Collisionless astrophysical shocks - collisionless shocks form in low density astrophysical plasmas via EM viscosities (i.e. collective interactions btw particles and underlying B field) - incomplete “thermalization” → non-Maxwellian tail → suprathermal particles : leak upstream of shock → streaming CRs induce MHD waves - accelerated to higher E via Fermi first order process - CRs are byproducts of collisionless shock formation May 17-19, th Korean Astrophysics Workshop KASI, Korea

the key ideas behind DSA (diffusive shock acceleration) - Alfven waves in a converging flow act as converging mirrors → particles are scattered by waves → cross the shock many times “Fermi first order process” u1 u2 shock front particle upstream downstream shock rest frame energy gain at each crossing converging mirrors May 17-19, th Korean Astrophysics Workshop KASI, Korea

simplest prediction of DSA theory - when non-linear feedback due to CR pressure is insignificant test particle theory: f(p) ~ p-q or N(E) ~ E-q+2 universal power-law q = 3r/(r-1) (r = r2/r1=u1/u2 compression ratio across the shock) determined solely by the shock Mach number - for strong gas shock (large M): r → 4 (g = 5/3 for gas adiabatic index) q → 4, f(p) dp= f0 p-4 dp or N(E)dE = N0 E-2 dE synchrotron jn ~ n-a , a = (q - 3)/2 → 0.5 spectral index ~ similar to observed values of “q” and “a” But DSA is very efficient, CR pressure is significant → nonlinear feedback of diffusive CRs to the shock structure May 17-19, th Korean Astrophysics Workshop KASI, Korea

1D Plane Shock simulations of DSA acceleration t=0 CR modified shocks - presusor + subshock - reduced Pg enhanced compression time evolution of the Ms = 5 shock structure at t = 0, pure gasdynamic shock with Pc = 0. no simple shock jump condition → need numerical simulations to calculate the CR acceleration efficiency precursor (Kang, Jones & Gieseler 2002) May 17-19, th Korean Astrophysics Workshop KASI, Korea

Thermal E CR E - kinetic energy flux through shocks Fk = (1/2)r1Vs3 - net thermal energy flux generated at shocks Fth = (3/2) [P2-P1(r2/r1)g] u2 = d(M) Fk - CR energy flux emerged from shocks FCR= h(M) Fk Egas r1 Vs= u1 thermalization efficiency: d(M) CR acceleration efficiency: h(M) ECR May 17-19, th Korean Astrophysics Workshop KASI, Korea

Shock waves in the large scale structure of the universe
(Ryu, Kang et al 2003, 2004) Numerical simulations - L cold dark matter cosmology L = 0.73, DM = 0.27, gas = 0.043, h=0.7, n = 1, 8 = 0.8 (no gas cooling, no heating, no feedbacks) - computational box: (100h-1 Mpc)3 10243 cells for gas and gravity, 5123 DM particles, Dx = h-1Mpc X-ray emissivity shock speed vsh = km s-1 and higher

X-ray emissivity distribution: time evolution (100 h-1 Mpc)3 10243 cells full box spinning May 17-19, th Korean Astrophysics Workshop KASI, Korea

X-ray emissivity shock waves sheet cluster filament (100 Mpc/h)2 2D slice rich, complex shock morphology: shocks “reveal” filaments and sheets (low density gas) May 17-19, th Korean Astrophysics Workshop KASI, Korea

velocity field and shocks in a cluster complex
Lx rgas T Ms (25 h-1Mpc)2 2D slice May 17-19, th Korean Astrophysics Workshop KASI, Korea

distribution of shock Mach no. May 17-19, th Korean Astrophysics Workshop KASI, Korea

time evolution of shocks around a cluster complex 28 x 37 (h-1 Mpc)2 slice 150 < vsh< 700 km/s vsh< 150 km/s vsh> 700 km/s external shocks internal shocks external shocks: high Mach no. outer surfaces of nonlinear struct. internal shocks: low Mach no. inside nonlinear structure May 17-19, th Korean Astrophysics Workshop KASI, Korea

statistics of Mach number distribution
(S Sshock/V, 1/S mean comoving distance btw shock surfaces) shock frequency S (external) / S(internal) = ~2 at z = 0 and larger in the past → external shocks are more common than internal shocks S = ~1/3 h-1Mpc with M > 1.5 at z = 0 → average inverse comoving distance between shock surfaces May 17-19, th Korean Astrophysics Workshop KASI, Korea

kinetic energy flux per unit comoving volume through shock surfaces
internal shocks are energetically more important than external shocks! May 17-19, th Korean Astrophysics Workshop KASI, Korea

Thermal E CR E - kinetic energy flux through shocks Fk = (1/2)r1Vs3 - net thermal energy flux generated at shocks Fth = (3/2) [P2-P1(r2/r1)g] u2 = d(M) Fk - CR energy flux emerged from shocks FCR= h(M) Fk Egas r1 Vs= u1 thermalization efficiency: d(M) CR acceleration efficiency: h(M) ECR May 17-19, th Korean Astrophysics Workshop KASI, Korea

energies passed through and produced at shocks:
integrated from z = 2 to 0 3 - CR acceleration  shocks with M = 2~5 - ECR accelerated at shocks = ~1/2 x Eth generated at shocks May 17-19, th Korean Astrophysics Workshop KASI, Korea

Effects of other processes?
(Kang, Ryu et al 2006 in preparation) three homogeneous simulations of L cold dark matter cosmology (data from R. Cen) L = 0.69, matter = 0.31, gas = 0.048, h=0.69, n = 0.97, 8 = 0.89 computational box (85 h-1 Mpc)3 with cells for gas & gravity, 5123 DM particles - adiabatic (gravity and gas pressure only) cooling/heating (heating mostly due to the UV background) cooling/heating+feedback (Efeedback = 3x10-6 Mgalaxyc2 as kinetic energy) (intended to be galactic winds, not jets) May 17-19, th Korean Astrophysics Workshop KASI, Korea

density-temperature plane
adiabatic cooling/heating rgas/rmatter T 108 104 106 102 100 10-2 May 17-19, th Korean Astrophysics Workshop KASI, Korea

temperature distribution
cooling/heating cooling/heating+feedback (21.2 h-1Mpc)2 2D slice May 17-19, th Korean Astrophysics Workshop KASI, Korea

evolution of WHIM (warm-hot intergalactic medium)
WHIM in cooling/heating+feedback WHIM in cooling/heating Mass weighted volume filling factorof about 0.05, then with density of 10 times The mean, we get 50% of mass in WHIM (Cen and Ostriker 2006) May 17-19, th Korean Astrophysics Workshop KASI, Korea

distribution of shock waves
(100 h-1Mpc)2 2D slice adiabatic May 17-19, th Korean Astrophysics Workshop KASI, Korea

distribution of shock waves
adiabatic cooling/heating (21.2 h-1Mpc)2 2D slice cooling/heating+feedback wind shock only May 17-19, th Korean Astrophysics Workshop KASI, Korea

statistics of shock waves
adiabatic shock frequency log(M) cooling/heating cooling/heating+feedback May 17-19, th Korean Astrophysics Workshop KASI, Korea log(v)

energetics of shock waves
energy fluxes per unit comoving volume through shock surfaces adiabatic cooling/heating cooling/heating+feedback the effcts of cooling/heating and feedback on shock energetics are not important!

Highest Energy accelerated at cluster accretion shocks
acc (p)~ 8 k(p)/Vs2 mean acceleration time loss = e. loss time scale due to CBR tacc = tloss  Emax ~ eV for Bohm Emax ~ eV for Jokipii (Kang, Rachen, Biermann 1997) tacc Bohm diffusion in parallel shocks  kB = rg v / 3 Jokipii diff. in perpendicular shocks  kJ ~ rg Vs = 3(Vs /c) kB ~ 0.01 kB Vs = 1000 km/s, B = 1 mG diff. along field lines and drift across field are limited by the finite size  E max = Z ba BR : return back to “Hillas” constraint, so E <1019 eV cluster accretion shocks (Ostrowski & Siemieniec-Ozieblo 2002) May 17-19, th Korean Astrophysics Workshop KASI, Korea

Averaged energy spectrum of CRs produced at shocks at z = 0 E-2.2 thermal leakage & test particle models adopted E-2.1 3 109 eV 1019 eV May 17-19, th Korean Astrophysics Workshop KASI, Korea

Summary - shock waves are common in the large scale structure of the Universe, which are consequences of structure formation V/Sshock = ~3h-1Mpc with M >1.5 at z=0 (V/Sshock = ~1h-1Mpc with M >1.5 at z=0 inside structures) - CRs are natural byproducts of dissipation at collisionless shocks Eth  shocks ECR/Eth ~ 1/2 at shocks => ECR ~ Eth at present - weaker internal shocks => heat gas and accelerate CR protons & electrons shocks with M = 2~4 contribute most - stronger external shocks => produce higher energy CRs up to ~1019 eV May 17-19, th Korean Astrophysics Workshop KASI, Korea

Thank you ! May 17-19, th Korean Astrophysics Workshop KASI, Korea

Dongsu Ryu (Chungnam National U, Korea)

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Dongsu Ryu (Chungnam National U, Korea)

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