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Galaxy Formation. James Binney Oxford University. TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: A A A A A A A. Outline. Cosmological clustering Scales introduced by baryons Timeline Chemical evolution Cores of Es Cooling flows. CDM Background.

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Galaxy formation

Galaxy Formation

James Binney

Oxford University

TexPoint fonts used in EMF.

Read the TexPoint manual before you delete this box.: AAAAAAA


  • Cosmological clustering

  • Scales introduced by baryons

  • Timeline

  • Chemical evolution

  • Cores of Es

  • Cooling flows

Cdm background
CDM Background

  • Power spectrum of fluctuations

  • ! filaments+voids

  • ! hierarchy of halos

  • Analytic model: Extended Press-Schechter theory

  • characteristic mass(z)

  • Halo characteristic velocity(M)

  • Halo mass fn

  • Halo merger prob

Primary secondary halos
Primary & secondary halos

  • Secondary halo: one that has fallen in to another halo

  • Survival time tfric ' tdyn(M/m)

  • Primary halo: one that hasn’t fallen in

  • P-S theory applies only to primary halos

  • Older theory didn’t believe in secondary halos

  • Primary/Secondary status changes sign of gas accretion/depletion

And baryons
And baryons?

  • Have e.m. interactions:

  • Short-range scattering

    • adiabatic/shock compressive heating

  • Exchange E with e.m. waves

    • emission of bremsstrahlung + line radiation;

    • photo + Compton heating

  • Can form stars and BHs, which heat surrounding matter

    • Mechanically (winds/jets/shocks)

    • photonically

Characteristic numbers
Characteristic numbers

  • Photo-heating

    • T'104K $ cs'10 km/s $ M=108M¯

  • SN heating

    • With Salpeter IMF get 1 SN / 200 M¯ of SF ! ESN=1044J of mechanical E

    • Tmax=(mp/200M¯)ESN/kB=3£107K

Numbers cont
Numbers (cont)

  • Gravitational heating

    • Rate of grav heating/unit mass

      • Hgrav=(GMH/r2)v=G½rv

    • Rate of radiative cooling/unit mass

      • Crad=¤(T)n2/(nmp)=¤½B/mp2

      • ¤(T) = ¤(T0)(T/T0)1/2 = ¤(T0)v/v0 with T0 ' 106K, v0 = 100 km/s

      • Crad = ¤(T0)fB½ v/(v0mp2) with fB=0.17

    • Hgrav/Crad = Gmp2v0r/fB¤(T0) = r/rcrit where rcrit=160kpc

    • ! Mcrit' 1012M¯

  • Bottom line: smaller systems never get hot

  • Galaxies don’t form by cooling


  • z'20: small-scale (M~106M¯) structures begin to collapse

  • Location: where long & short waves at crests, ie what will be centres of rich clusters

  • Voids shepherd matter into filaments

  • Larger & larger regions collapse, driving mergers of substructures

  • Voids merge too

  • A substructures survives if it falls into sufficiently bigger halo

  • Action spreads from densest to less dense regions (“downsizing”)

  • Initially Universe extremely cold (T<1K)

  • At z'6 photo heated to 104K

  • Halos less massive than 108 M¯ subsequently can’t retain gas

  • In low-density regions ! large population dark-dark halos?

Timeline contd
Timeline (contd)

  • At any location scale of halo formation increases, as does Tvir

  • Until Tvir=106K, M=1012M¯ SN-heated gas escapes

  • Until Tvir=106K, M=1012M¯ infalling gas cold

  • Halos with M>1012M¯ acquire hot atmospheres

  • Heating by AGN counteracts radiative cooling

  • Hot gas evaporates limited cold infall ! “quenching” of SF

Chemical evolution
Chemical evolution

  • Closed-box model

  • Z=Mh/Mg (Z¯=0.02)

  • Instantaneous recycling

  • ±Mh = p±Ms-Z±Ms = (p-Z)±Ms

  • ±Z = ±(Mh/Mg) = (±Mh-Z±Mg)/Mg

  • Eliminate ±Mh!± Z = -p±ln(Mg)

  • ! Z(t)=-p ln[Mg(t)/Mg(0)]

  • Ok for gas-rich dwarfs but not dSph!

  • Ms[<Z(t)]=Ms(t)=Mg(0)-Mg(t)=Mg(0)(1-e-Z/p)

  • Ms(<®Z)/Ms(<Z)=(1-x®)/(1-x) where x=Mg(t)/Mg(0)

  • G-dwarf problem: with x=0.1 Ms(<Z¯/4)'0.49Ms but only 2% stars <0.25Z¯

In or out
In or out?

  • The box is open!

  • Outflow or inflow?

  • Arguments for inflow:

    • SFR ' const in solar nhd (Hipparcos)

    • S0 galaxies are spirals that have ceased SF (TF relation & specific GC frequency); they are also in locations where we expect inflow to have been reversed (Bedregal et al 2007)

  • Arguments for outflow:

    • in rich clusters ~half of heavy elements are in IGM

    • in M82 you see ouflow (probably in Galaxy too)

    • application of leaky box to globular-cluster system

Leaky box model
Leaky-box model

  • dMt/dt=-c dMs/dt

  • !

  • Can also apply to centres of ellipticals with c(¾) by equating E of ejection to ESN (S5.3.2 of Binney & Merrifield)

® enhancement

  • Most “® elements” (O, Ne, Mg, Si, S, A, Ca) ejected by core-collapse SNe; ¿~10Myr

  • Majority of Fe injected by type 1a SNe; ¿~1Gyr

  • Spheroids (metal-poor halo) ® enhanced (relative to Sun)

  • Implies SF complete inside 1Gyr

Centres of es
Centres of Es

  • Photometry of Es fitted by

Lauer + 07

Conclude: on dry merging cores

destroyed by BHs; in gas-rich

mergers reformed by SF

Nipoti & Binney 07

Cooling flows mass dropout
Cooling flows: mass dropout

  • In 1980s & 90s X-ray profiles interpreted on assumption that (i) steady-state, (ii) no heating

  • Imply diminishing flow to centre

  • ICM multiphase (Nulsen 86)

  • Field instability analysis implied runaway cooling of overdense regions (tcool/ 1/)

  • Cooler regions radiate all E while at rÀ 0

  • Predicts that there should be (a) cold gas and (b) line radiation from T<106K throughout inner cluster

Stewart et al 84

G modes
G modes

  • Malagoli et al (87): overdense regions just crests of gravity waves

  • In half a Brunt-Vaisala period they’ll be underdensities.

  • Oscillations weakly overstable (Balbus & Soker 89) but in reality probably damped.

  • Conclude: over timescale <tcool heating must balance radiative losses

  • Systems neither cooling nor flowing!

2001 chandra xmm newton
2001 – Chandra & XMM-Newton

  • XMM doesn’t see lines of <106K gas

  • XMM shows that deficit of photons at <1keV not due to internal absorption

  • But associated with “floor” T' Tvir/3

  • Chandra shows that radio plasma has displaced thermal plasma

(Bohringer et al 02)

(Peterson et al 02)

Outward increasing entropy
Outward increasing entropy

Omma thesis 05

Donahue 04

Summary cooling flows
Summary (cooling flows)

  • Hot atmospheres not thermally unstable: will cool first @ centre

  • Clear evidence that weak radio sources associated with BH keep atmospheres hot

  • Mechanism: probably Bondi accretion at rate controlled by central density

  • Result: halos M>1012M¯ have little SF

  • Smaller halos that fall into such big halos gradually sterilized by ablation too

  • Hence decline in cosmic SF rate at current epoch

Papers to read
Papers to read

  • Dekel & Silk 1986

  • Frenk & White 1991

  • Benson et al 2003

  • Cattaneo et al 2006