Cosmological Shocks and Their Signatures

Transcription

1 Cosmological Shocks and Their Signatures Dongsu Ryu (Chungnam National U, Korea) Hyesung Kang (PNU, Korea), Renyi Ma (CNU, Korea), Jungyeon Cho (CNU, Korea), David Porter (U of Minnesota), T. W. Jones (U of Minnesota) - Shock waves in the large scale structure of the universe from numerical simulation - Cosmic rays accelerated at the shocks and non-thermal radiation - Turbulence in the intracluster medium

2 Overveiw large-scale structure formation gravitational collase & flow motion cosmological shocks shock shock dissiation the main channel to the gravitational energy to the intergalactic medium other sources, such as AGNs of heat, CRs, turbulence and magnetic field generation of heat acceleration of CRs generation of vorticity genera. of magnetic fields radiation from CRs

3 Satial distribution of cosmological shocks in the large-scale structure of the universe X-ray emissivity (Ryu, Kang, Hallman, Jones 2003) shock waves cluster ancake filament rich, comlex shock morhology: shocks reveal filaments and sheets (low density gas)

4 Velocity field and shocks in a cluster comlex X-ray ρ gas T shocks (25 h -1 Mc) 2 2D slice

5 Mach number distribution of shocks around the cluster comlex

6 X-ray Observation of a shock in the ICM M ~ 2.1 temerature X-ray observation of A520 -> a shock of M ~ 2.1 (Markevitch & Vikhlinin 2007) X-ray emssivity gas density

7 size of arcs: ~ 2 Mc x 1.6 Mc Observation of accretion shocks or merger shocks? radio arcs in A3376 (Bagchi et al 2006) radio + X-ray radio + otical

8 Frequency and energetics of cosmological shocks shock frequency kinetic energy flux through shock surfaces -S = ~1/3 h -1 Mc with M > 1.5 at z = 0 (S = ~1 h -1 Mc with M > 1.5 at z = 0 inside nonlinear structures) <- average inverse comoving distance between shock surfaces - shocks with M <~ a few (weak), V s ~ 2,000 km/s are energetically most imortant (Kang, Ryu et al 2007)

9 Cosmological shocks in different environments in the WHIM with 10 5 < T < 10 7 in hot gas with T > 10 7 in clusters and grous shocks with V s ~ 1,000-2,000 km/s (M s ~ a few) are common in clusters and grous

10 (Kang, Ryu, et al 2007) (Pfrommer et al 2006) (Vazza et al 2008) energetics of cosmological shocks in different works - agreement is OK - weak shocks are energetically most imortant (Skillman et al 2008)

11 Cosmic rays accelerated at cosmological shocks key ideas behind DSA (diffusive shock acceleration) - Alfven waves in a converging flow act as converging mirrors articles are scattered by waves article cross the shock many times Fermi first order rocess u 1 u ~ u energy gain at each crossing converging mirrors u 2 downstream shock front ustream shock rest frame

12 Cosmic ray acceleration efficiency at shocks E th E CR ρ 1 V s = u 1 - kinetic energy flux through shocks F k = (1/2)r 1 V s 3 - net thermal energy flux generated at shocks F th = (3/2) [P 2 -P 1 (r 2 /r 1 ) g ] u 2 = δ(m) F k - CR (rotons) energy flux emerged from shocks F CR = η(m) F k thermalization efficiency: δ(m) CR acceleration efficiency: η(m) (rotons)

13 - most relevant to shocks in clusters ε B =B 0 /B er - however, the hysics of weak shocks are not well understood slo = on the to of it, shocks with reexisting CRs have not studied so far thermalization efficiency: δ(m) CR acceleration efficiency: η(m) for quasi-arallel shocks (Ma, Kang, Ryu in rearation)

14 Cosmic rays accelerated at cosmological shocks: integrated over the evolution of the universe black lines kinetic energy flux through shocks thin lines thermal energy generated at shocks thick lines CR energy I, II, III, IV, V with different CR acceleration efficiencies 3 CR accelerated mostly at shocks with M = 2~5 V s ~ 1,000 2,000 km/s

15 Predicted fraction of CR energy in different environments with reexisting CRs of P CR /P therm ~ in downstream for weak shocks E CR /E therm -> P CR /P therm ~ (E CR /E therm ~ ) is exected in the ICM outside of clusters -> P CR /P therm would ne higher clusters

16 Sectral distribution of CRs accelerated at cosmological shocks cosmic ray rotons (CR) at each shocks - sloe <- shock Mach number - maximum energy <- acceleration time ~ age of the universe - amlitude <- total CR energy accelerated and then assumed to be advecetd without losing energy rimary cosmic ray electrons (CRe) at each shocks - sloe <- same as that for cosmic ray rotons - maximum energy <- acceleration time ~ cooling time - amlitude <- the energy of CRe = a fraction of the energy of CR and then assumed to be advecetd and lose the energy by cooling secondary cosmic ray electrons (CRe) In the IGM, the creation rate due to roton-roton collision balances the lose rate due to cooing (Ma, Ryu, Kang in rearation)

17 rimary cosmic ray electrons cosmic ray rotons secondary cosmic ray electrons from - Resulting sectrum of CRs inside the whole comutational box secondary cosmic ray electrons from hotoair & hoto-ion the ratio of E CRe /E CR at shocks is arbitrary in this lot

18 Satial distribution of CRs rimary cosmic follows the distribution ray electrons of shocks - extended area of the region (85 h-1 Mc)2 rojected over the deth of 85 h-1 Mc follows the distribution of matter - concentrated cosmic ray secondary cosmic ray rotons electrons from -

19 A model for the intergalactic magnetic field (IGMF) (Ryu, Kang, Cho, Das 2008) filaments - vorticity generated at curved shocks and also due to baroclinity - cascades into turbulence - roduce the IGMF by turbulence dynamo strength and energy of turbulence from simulation clusters E B 2 B = = φ( ω t) 8π Ε turb conversion factor from searate MHD turbulence simulations no fine tuning to normalize B! ρ, v B

20 Resulting magnetic fields in the large-scale structure of the universe at z = 0 averaged magnetic field strength at z = 0 - inside clusters <B> ~ a few µg - around clusters (T > 10 7 K) <B> ~ 0.1 µg - in filaments (10 5 K < T < 10 7 K, or WHIM) <B> ~ 10 ng magnetized cosmic web distribution of the intergalactic magnetic field in a (~100 h-1 Mc) 3 box G G 10-5 G

21 Non-thermal radiations We are currently building a radiation code to calculate the sectral distributions of - inverse-comton - synchrotron - non-thermal bremsstrahlung - gamma-ray from roton-roton collision - gamma-ray from hoto-air and hoto-ion Still in rogress! No sectral distributions Satial distributions (reliminary) (Ma, Ryu, Kang in collaboration with Edmon, Jones)

22 thermal bremsstrahlung IC (CRe) synchrotron (CRe + B) area of the region (85 h-1 Mc)2 rojected over the deth of 85 h-1 Mc extended distribution Satial distribution of non-thermal radiations from rimary CRe

23 thermal bremsstrahlung IC (CRe) synchrotron (CRe + B) area of the region (85 h -1 Mc) 2 rojected over the deth of 85 h -1 Mc Satial distribution of non-thermal radiations from secondary CRe

24 Turbulence in the intergalactic medium large-scale structure formation gravitational collase & flow motion cosmological shocks shock shock dissiation the main channel to the gravitational energy to the intergalactic medium other sources, such as AGNs of heat, CRs, turbulence and magnetic field generation of heat acceleration of CRs generation of vorticity genera. of magnetic fields vorticity into turbulence further am. of mag. field

25 Vorticity generated at cosmological shocks Β = 0 directly at curved shocks curved shock ϖ cs at ostshock ~ 2 1 ( ρ2 ρ1) ρ ρ 2 U n R Β 0 different jum of B (Bernoulli function) ρ 1 ρ 2 U n R reshock density ostshock density reshock flow seed unit normal to shock surf. curvature radius of surf. by the baroclinic term 1 ϖ bc = ρ 2 ρ baroclinity constant ρ constant due to entroy variation induced at shocks

26 X-ray Vorticity in a cluster comlex shocks (Ryu, Kang, Cho, Das 2008) velocity field ρ curl(v) x curl(v) (25 h -1 Mc) 2 2D slice 1500 kms kms -1 6 kms kms kc / 300 kc / 300 kc / 300 kc

27 the turbulence energy of in the intergalactic medium, assuming that all the energy of vortical motions goes to turbulence M turb < 1 (subsonic turbulence) in clusters and grous M turb ~ 1 (transonic turbulence) in filaments clusters Eturb/Etherm ~ 0.1 in clusters

28 with 256 3, 512 3, , grid zones Simulations for the study of comressible turbulence in the intracluster medium E kin /E therm ~ 0.1 at saturation M s ~ 0.45 B o ~ 0 (no regular field) E mag /E kin ~ 1/2 at saturation in run (Ryu, Porter, Jones, Cho in rogress)

29 Power sectrum with 256 3, 512 3, , grid zones K 5/3 P vel (k) with infinite resolution E mag /E kin ~ 2/3 is exected K 5/3 P mag (k)

30 Estimated non-thermal comonents in the ICM energy fraction - E CR /E therm ~ E turb-kin /E therm ~ E turb-mag /E therm ~ contribution to Pressure - P CR /P therm ~ P turb-kin /P therm ~ P turb-mag /P therm ~ 0.1 P therm = 2/3 E therm P CR = 1/3 E CR P turb-kin = 2 E turb-kin P turb-mag = E turb-mag Non-thermal energy and ressure fractions increase as move outwards

31 Power sectrum the ower in the comressional mode ~ 1/10 x the ower in the solenoidal mode (M s ~ 0.45)

32 Satial distribution of div(v) or comressible mode in a slice shocks

33 PDF of div(v) shocks with Mach number of a few are common! (M s ~ 0.45)

34 Basin lasma hysics for the ICM mean free-ath for electron-roton relaxation few kc cm ~ a ) (cm (K) ln 10 ~ ~ Λ e e e n T l l mean free-ath for electron-electron & roton-roton collisions ~ 100 kc ~ 2 1 e e m m l l l L < viscous regime e l L l < < l e L > collisional regime e T T kinetic viscosity t l l 2 therm ~ ~ υ ν resistivity e t c 2 ) / ( ~ ω η = 2 1/ 2 4 e e m e n π ω magnetic Prandtle number or larger ~ η ν = P m

35 MHD turbulence with high magnetic Prandtle number (P m =50) viscous scale (Brandenburg, Subramanian 2005) k P mag (k) at saturation P vel (k) at saturation with grid zones

36 Thank you!