Документ взят из кэша поисковой машины. Адрес оригинального документа : http://hea.iki.rssi.ru/conf/hea2007/presentations.orig/25.12.07/medvedev.pdf Дата изменения: Sat Dec 29 14:50:22 2007 Дата индексирования: Tue Oct 2 01:15:41 2012 Кодировка: Поисковые слова: п п п п п п п п п п п п п п п п п п

Mikhail Medvedev (University of Kansas)

HEA-2007, IKI, Moscow


Missing baryons in inter-cluster gas
Afshordi, et al, 2007, astro-ph/0612700

35% +/- 8%

Sample of 260 clusters WMAP SZ 3yr data Compared with 11 simulated clusters Assumed: Universal NFW profile Self-similarity Isothermal gas


Possible explanations
Observed stellar mass in galaxies: ~ 10% (Lin, et al, 2003) Therefore, about 20% +/- 8% remains unaccounted Cosmological simulations with cooling and star formation (Kravtsov, et al, 2007; Nagai, et al 2007) give observed values of ICM gas fraction but a factor 2-3 more stellar mass Diffuse intracluster light Cold clouds in the ICM, T<10K, low covering fraction (Dwarakanath, et al, 1994) Thermal conduction removal of thermal energy (Zakamska & Narayan, 2003) Evaporation of gas (Loeb 2007) Can account only 10-50% of stars (Monaco, et al. 2006, Gonzalez, et al, 2005, ...more...) No observational constraints

Simulations indicate that the effect is small (Dolag, et al, 2004)

Claimed: can explain ~10-20%


Evaporation of ICM gas
Loeb, 2007 Evaporated fraction

free streaming

Maxwellian PDF

diffusion

Evaporated fraction ~10% is highly overestimated ->> effect of B-fields is grossly underestimated


Particle motion in tangled magnetic fields
B=0 m
fp

Random B · Field line wandering · Magnetic mirroring Lc
orrel

"=

#

mfp thermal

V

$"

Spitzer

Lc r
L arm or

orrel

!

Homogeneous B rL a r m o r

"

effective

~f
mirror

mirror

L

corrrel

Vthermal # f B"

Spitzer

fB = f

f

field

" || =

#

mfp thermal

V

=V

2 thermal

" & = rLarmorVthermal
f B = 10
.12

' =) ) (

1 $ % " Spitzer 3 rLarmor * ," Spitzer - f B" 3# mfp , +

Spitzer

<< 1

Even in collisionless plasma, particle motion ! diffusive, due to randomness of magnetic is fields of MHD intra-cluster turbulence. ->> particle transport is strongly suppressed if fB<<1

!


Transport suppression evaluation
Narayan & Medvedev, 2001
f
field~

Malyshkin & Kulsrud, 2001
1/100

f

field~

1/5 single-scale B

Lc f
m irro r

o rre l

~Mpc

~1/100

multi-scale B (MHD turb.)

Effective upper limit on transport suppression:

· In general, fB depends on the ICM B-field correlation length, gas temperature and density · Transport is even more suppressed in time-dependent (MHD & hydro) turbulence (Lazarian, 2006)


Evaporation fraction
Medvedev, 2007 Evaporation occurs from a thin layer of thickness:

Only ~1% of gas can evaporate during the Hubble time

L

correl=

10kpc, c=2

ldiff ~0.1 rvirial rvirial

L

correl=

1kpc, c=2

L

correl=

1kpc, c=8

T=15keV, c=2 T=5keV, c=2 T=5keV, c=8


Conclusions
Observed stellar mass in galaxies: ~ 10% (Lin, et al, 2003) Therefore, about 20% +/- 8% remains unaccounted Cosmological simulations with cooling and star formation (Kravtsov, et al, 2007; Nagai, et al 2007) give observed values of ICM gas fraction but a factor 2-3 more stellar mass Diffuse intracluster light Cold clouds in the ICM, T<10K, low covering fraction (Dwarakanath, et al, 1994) Thermal conduction removal of thermal energy (Zakamska & Narayan, 2003) Evaporation of gas (Loeb 2007) Can account only 10-50% of stars (Monaco, et al. 2006, Gonzalez, et al, 2005, ...more...) No observational constraints

?

Simulations indicate that the effect is small (Dolag, et al, 2004)

Can account for ~1-2% missing mass at most