Gh2005 gas dynamics in clusters ii
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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

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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-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 masses → integrate r

  • Total masses → hydrostatic equilibrium

  • Dark matter Mdm = M – Mgal - Mgas


Total Masses Profiles

XMM/Newton (Pointecouteau et al)

(curves are NFW fits)


Gas Fraction Profiles

Chandra (Allen et al)

(r2500≈0.25 rvir)


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.)

  • 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

IX

  • Central peaks in X-ray surface brightness

cooling core non-cooling core (Coma)


Cooling Cores in Clusters

  • Central peaks in X-ray surface brightness

  • Temperature gradient, cool gas at center


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 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.)

  • 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 (cont.)

  • Steady-state cooling of homogeneous gas


Cooling Cores in Clusters (cont.)

  • Bremsstrahlung cooling

  • Reasonable fit to X-ray surface

  • brightness

  • Ṁ ~100 M/yr

r-1

ln IX

r-3

ln r


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)

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?

  • 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 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

  • ≳ 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)

Blanton et al.


Radio Contours (Burns)


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

  • 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

Perseus

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.)

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

Ghost bubbles have low frequency radio


Buoyant “Ghost” Bubbles

Perseus

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

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

  • Gas in shells is cool

  • Pressure in shells ≈ outside

  • No large pressure jumps (shocks)


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

  • 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

  • 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

Epol

Epol

B||


Cooling

  • Isobaric cooling time in shells are tcool≈ 3 x 108 yr≫ ages of radio sources

  • Cooler gas at 104 K located in shells


Hα + [N II] contours (Baum et al.)


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?

  • 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


Examples

  • 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

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.


Limit Cycle?


Cluster Formation:Mergers and Accretion

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

Virgo Consortium


Cluster Formation fromLarge Scale Structure

Lambda CDM - Virgo Consortium

z=2 z=1 z=0


Cluster Formation (cont.)

  • Clusters form within LSS filaments, mainly at intersections of filaments

  • Clusters form through

    mixture of small and

    large mergers

    Major mergers

    Accretion

  • Clusters form today and

    in the past

PS merger tree: Mass vs. time


Cluster Formation (cont.)

Lambda CDM - Virgo Consortium

z=2 z=1 z=0


Spherical Accretion Shocks

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

    Zeldovich)

  • Cold gas → very strong

    shocks

  • Accretion shocks at very

    large radii (≳rvir~2 Mpc)

  • No direct observations

    so far

l ≡ r / rta (turn around radius)


Accretion Shocks (cont.)

z=2 z=1 z=0

  • Growth of clusters not spherical

  • Accretion episodic (mergers)

  • IGM not cold


Accretion Shocks (cont.)

  • Growth of clusters not spherical 40x40 Mpc

  • Accretion episodic (mergers)

  • IGM not cold

40x40 Mpc

(Jones et al)


Accretion Shocks (cont.)

~40x40 Mpc

External (accretion)

& internal (merger)

shocks

(Ryu & Kang)


Accretion Shocks (cont.)

  • Mach numbers ℳ ≡ vs / cs ~ 30

  • Yf= kinetic energy, Yth = thermal energy


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

  • 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

  • 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 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.)

  • Additions

    • Magnetic fields (MHD)

    • Cosmic rays, particle acceleration

    • Transport processes

    • AGNs

  • Issues

    • Spatial resolution, particularly in cores (AMR, SPH)

    • Overcooling, galaxy formation, feedback


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