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GH2005 Gas Dynamics in Clusters II. Craig Sarazin Dept. of Astronomy University of Virginia. Cluster Merger Simulation. A85 Chandra (X-ray). De-Projected Gas Profiles. De-project X-ray surface brightness profile → gas density vs. radius, r (r)

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gh2005 gas dynamics in clusters ii

GH2005Gas Dynamics in Clusters II

Craig Sarazin

Dept. of Astronomy

University of Virginia

Cluster Merger Simulation

A85 Chandra (X-ray)

de projected gas profiles
De-Projected Gas Profiles
  • De-project X-ray surface brightness profile → gas density vs. radius, r(r)
  • De-project X-ray spectra in annuli → T(r)
  • Pressure P = rkT/(mmp)
gas and total masses
Gas and Total Masses
  • Gas masses → integrate r
  • Total masses → hydrostatic equilibrium
  • Dark matter Mdm = M – Mgal - Mgas
total masses profiles
Total Masses Profiles

XMM/Newton (Pointecouteau et al)

(curves are NFW fits)

gas fraction profiles
Gas Fraction Profiles

Chandra (Allen et al)

(r2500≈0.25 rvir)

masses of clusters
Masses of Clusters
  • Cluster total masses 1014 – 1015 M
    • 3% stars and galaxies
    • 15% hot gas
    • 82% dark matter
    • Clusters are dominated by dark matter
    • Earliest and strongest evidence that Universe was dominated by dark matter
masses of clusters cont
Masses of Clusters (cont.)
  • Mass gas ~ 5 x mass of stars & galaxies!
    • Hot plasma is dominant form of observed matter in clusters
  • Most of baryonic matter in Universe today is in hot intergalactic gas
  • Compare baryon fraction in clusters to average value in Universe from Big Bang nucleosynthesis
    • ΩM=0.3, early evidence that we live in a low density Universe
  • Compare fraction baryons high vs. low redshift, assume constant
    • Evidence for accelerating Universe (dark energy)
cooling cores in clusters
Cooling Cores in Clusters


  • Central peaks in X-ray surface brightness

cooling core non-cooling core (Coma)

cooling cores in clusters1
Cooling Cores in Clusters
  • Central peaks in X-ray surface brightness
  • Temperature gradient, cool gas at center
cooling cores in clusters2
Cooling Cores in Clusters
  • Central peaks in X-ray surface brightness
  • Temperature gradient, cool gas at center
  • Radiative cooling time tcool < Hubble time
  • tcool ~ 2 x 108 yr
cooling cores in clusters3
Cooling Cores in Clusters
  • Central peaks in X-ray surface brightness
  • Temperature gradient, cool gas at center
  • Radiative cooling time tcool < Hubble time
  • Always cD galaxy at center
  • Central galaxies generally have cool gas (optical emission lines, HI, CO), and are radio sources
cooling cores in clusters cont
Cooling Cores in Clusters (cont.)
  • Theory:
  • X-rays we see remove thermal energy from gas
  • If not disturbed, gas cools & slowly flows into center
  • Gas cools from ~108 K → ~107 K at ~100 M/yr
cooling cores in clusters cont1
Cooling Cores in Clusters (cont.)
  • Steady-state cooling of homogeneous gas
cooling cores in clusters cont2
Cooling Cores in Clusters (cont.)
  • Bremsstrahlung cooling
  • Reasonable fit to X-ray surface
  • brightness
  • Ṁ ~100 M/yr


ln IX


ln r

the cooling flow problem
The Cooling Flow “Problem”
  • Where does the cooling gas go?
  • Central cD galaxies in cooling flows have cooler gas and star formation, but rates are ~1-10% of X-ray cooling rates from images
  • Both XMM-Newton and Chandra spectra → lack of lines from gas below ~107 K
high res spectrum xmm newton
High-Res. Spectrum (XMM-Newton)

Peterson et al. (2001)

Brown line = data, red line = isothermal 8.2 keV model, blue line = cooling flow model, green line = cooling flow model with a low-T cutoff of 2.7 keV

how much gas cools to low temperature
How Much Gas Cools to Low Temperature?
  • Gas cools down to ~1/2-1/3 of temperature of outer gas (~2 keV)
  • Amount of gas cooling to very low temperatures through X-ray emission ≲ 10% of gas cooling at higher temperature

Cooling gas now consistent with star formation rates and amount of cold gas

heat source to balance or reheat cooling gas
Heat Source to Balance or Reheat Cooling Gas?
  • Heat source to prevent most of cooling gas from continuing to low temperatures:
    • Heat conduction, could work well in outer parts of cool cores if unsuppressed
      • Works best for hottest gas Q ∝ T7/2, how to heat mainly cooler gas?
    • Supernovae?
    • AGN = Radio sources
radio sources in cooling flows
Radio Sources in Cooling Flows
  • ≳ 70% of cooling flow clusters contain central cD galaxies with radio sources, as compared to 20% of non-cooling flow clusters
  • Could heating from radio source balance cooling?
a2052 chandra
A2052 (Chandra)

Blanton et al.

other radio bubbles
Other Radio Bubbles

Hydra A

Abell 133

Abell 262

Blanton et al.

Fujita et al.

McNamara et al.

Abell 2029

Abell 85

Clarke et al.

Kempner et al.

morphology radio bubbles
Morphology – Radio Bubbles
  • Two X-ray holes surrounded by bright X-ray shells
  • From deprojection, surface brightness in holes is consistent with all emission projected (holes are empty)
  • Mass of shell consistent with mass expected in hole

X-ray emitting gas pushed out of holes by the radio source and compressed into shells

buoyant ghost bubbles
Buoyant “Ghost” Bubbles


Abell 2597

Fabian et al.

McNamara et al.

  • Holes in X-rays at larger distances from center
  • No radio, except at very low frequencies (Clarke et al.)
buoyant ghost bubbles cont
Buoyant “Ghost” Bubbles (Cont.)

Abell 2597 – 327 MHz Radio in Green (Clarke et al.)

Ghost bubbles have low frequency radio

buoyant ghost bubbles1
Buoyant “Ghost” Bubbles


Abell 2597

Fabian et al.

McNamara et al.

  • Holes in X-rays at larger distances from center
  • No radio, except at very low frequencies (Clarke et al.)
  • Old radio bubbles which have risen buoyantly
entrainment of cool gas
Entrainment of Cool Gas

M87/VirgoYoung et al.

A133 --- X-ray red, Radio greenFujita et al.

  • Columns of cool X-ray gas from cD center to radio lobe
  • Gas entrained & lifted by buoyant radio lobe?
temperatures pressures
Temperatures & Pressures
  • Gas in shells is cool
  • Pressure in shells ≈ outside
  • No large pressure jumps (shocks)
temperatures pressures1
Temperatures & Pressures
  • Gas in shells is cool
  • Pressure in shells ≈ outside
  • No large pressure jumps (shocks)

Bubbles expand ≲ sound speed

Pressure in radio bubbles ≈

pressure in X-ray shells

  • Equipartition radio pressures are ~10 times smaller than X-ray pressures in shells!?
additional pressure sources
Additional Pressure Sources
  • Magnetic field larger than equipartition value?
  • Lots of low-energy relativistic electrons?
  • Lots of relativistic ions?
  • Very hot, diffuse thermal gas?
    • Jet kinetic energy thermalized by “friction” or shocks?
    • Hard to detect hot gas in bubbles because of hot cluster gas in fore/background (but, may have been seen in MKW3s (Mazzotta et al.) In most clusters, just lower limits on kT ≳ 10 keV
limits from faraday depolarization
Limits from Faraday Depolarization
  • Radio bubbles have large Faraday rotation, but strong polarization
    • Faraday rotation ∝ neB∥
    • External thermal gas → strong Faraday rotation and polarization
    • Internal thermal gas → Faraday depolarization
  • Gives upper limit on ne
  • Given pressure, gives lower limit on T
  • kT ≳ 20 keV in most clusters if thermal gas is pressure source




  • Isobaric cooling time in shells are tcool≈ 3 x 108 yr≫ ages of radio sources
  • Cooler gas at 104 K located in shells
x ray shells as radio calorimeters
X-ray Shells as Radio Calorimeters
  • Energy deposition into X-ray shells from radio lobes (Churazov et al.):
  • E ≈ 1059 ergs in Abell 2052
  • ~Thermal energy in central cooling flow,

≪ total thermal energy of intracluster gas

  • Repetition rate of radio sources ~ 108 yr(from buoyancy rise time of ghost cavities)

Internal bubble energy

Work to expand bubble

can radio sources offset cooling
Can Radio Sources Offset Cooling?
  • Compare
    • Total energy in radio bubbles, over
    • Repetition rate of radio source based on buoyancy rise time of bubbles
    • Cooling rate due to X-ray radiation
  • A2052: E = 1059 erg

E/t = 3 x 1043 erg/s

kT = 3 keV, Ṁ = 42 M/yr

Lcool = 3 x 1043 erg/s ☑

  • Hydra A: E = 8 x 1059 erg

E/t = 2.7 x 1044 erg/s

kT = 3.4 keV, Ṁ = 300M/yr

Lcool = 3 x 1044 erg/s ☑

  • A262: E = 1.3 x 1057 erg

E/t = 4.1 x 1041 erg/s

kT = 2.1 keV,Ṁ = 10M/yr

Lcool = 5.3 x 1042 erg/s ☒

(but, much less powerful radio source)

Blanton et al.

McNamara et al.

Blanton et al.

x ray ripples
X-ray Ripples

Abell 2052 Chandra Unsharp Masked

How does radio source heat

X-ray gas?

Perseus (Fabian et al.)

X-ray ripples = sounds waves

or weak shocks

Viscous damping heats gas?

But, is Perseus unique?

Abell 2052 (Blanton et al.)

Also has ripples, l≈ 11 kpc,

P ≈ 1.4 x 107 yr

Blanton et al.

cluster formation mergers and accretion
Cluster Formation:Mergers and Accretion

Clusters from hierarchically, smaller things form first, gravity pulls them together

Virgo Consortium

cluster formation from large scale structure
Cluster Formation fromLarge Scale Structure

Lambda CDM - Virgo Consortium

z=2 z=1 z=0

cluster formation cont
Cluster Formation (cont.)
  • Clusters form within LSS filaments, mainly at intersections of filaments
  • Clusters form through

mixture of small and

large mergers

Major mergers


  • Clusters form today and

in the past

PS merger tree: Mass vs. time

cluster formation cont1
Cluster Formation (cont.)

Lambda CDM - Virgo Consortium

z=2 z=1 z=0

spherical accretion shocks
Spherical Accretion Shocks
  • Self-similar solution for spherical accretion of cold gas in E-dS Universe (Bertschinger 1985;(earlier work Sunyaev &


  • Cold gas → very strong


  • Accretion shocks at very

large radii (≳rvir~2 Mpc)

  • No direct observations

so far

l ≡ r / rta (turn around radius)

accretion shocks cont
Accretion Shocks (cont.)

z=2 z=1 z=0

  • Growth of clusters not spherical
  • Accretion episodic (mergers)
  • IGM not cold
accretion shocks cont1
Accretion Shocks (cont.)
  • Growth of clusters not spherical 40x40 Mpc
  • Accretion episodic (mergers)
  • IGM not cold

40x40 Mpc

(Jones et al)

accretion shocks cont2
Accretion Shocks (cont.)

~40x40 Mpc

External (accretion)

& internal (merger)


(Ryu & Kang)

accretion shocks cont3
Accretion Shocks (cont.)
  • Mach numbers ℳ ≡ vs / cs ~ 30
  • Yf= kinetic energy, Yth = thermal energy
accretion shocks cont4
Accretion Shocks (cont.)
  • Accretion shocks at large radii in very low density gas
  • X-ray emission ∝ (density)2 → very faint, never seen so far
  • Radio relics?
  • Eventually, SZ images? (SZ ∝ pressure)

Growth of LSS → most IGM is now hot, most baryons in diffuse, hot IGM

cluster mergers
Cluster Mergers
  • Clusters form hierarchically
  • Major cluster mergers, two subclusters, ~1015 M collide at ~ 2000 km/s
  • E (merger) ~ 2 x 1064 ergs
  • E (shocks in gas) ~ 3 x 1063 ergs

Major cluster mergers are most energetic

events in Universe since Big Bang


Abell 85 Merger

ChandraX-ray Image

Kempner et al

thermal effects of mergers
Thermal Effects of Mergers
  • Heat and compress ICM
  • Increase entropy of gas
  • Boost X-ray luminosity, temperature, SZ effect
  • Mix gas
  • Disrupt cool cores
  • Produce turbulence
  • Provide diagnostics of merger kinematics
numerical hydrodynamics of mergers
Numerical Hydrodynamics of Mergers
  • Numerical N-body for collisionless dark matter, galaxies
  • Numerical hydrodynamics for gas
  • Initial conditions
    • Draw from cosmological LSS simulations, resample at higher resolution
    • Set up individual binary mergers to test physics
  • Cooling by radiation
  • Preheating, galaxy formation
numerical hydrodynamics cont
Numerical Hydrodynamics (cont.)
  • Additions
    • Magnetic fields (MHD)
    • Cosmic rays, particle acceleration
    • Transport processes
    • AGNs
  • Issues
    • Spatial resolution, particularly in cores (AMR, SPH)
    • Overcooling, galaxy formation, feedback