Galaxy Formation - PowerPoint PPT Presentation

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Galaxy Formation

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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 ... – PowerPoint PPT presentation

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Title: Galaxy Formation


1
Galaxy Formation
  • James Binney
  • Oxford University

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2
Outline
  • Cosmological clustering
  • Scales introduced by baryons
  • Timeline
  • Chemical evolution
  • Cores of Es
  • Cooling flows

3
CDM Background
  • Power spectrum of fluctuations
  • ! filamentsvoids
  • ! hierarchy of halos
  • Analytic model Extended Press-Schechter theory
  • characteristic mass(z)
  • Halo characteristic velocity(M)
  • Halo mass fn
  • Halo merger prob

4
Primary secondary halos
  • Secondary halo one that has fallen in to another
    halo
  • Survival time tfric ' tdyn(M/m)
  • Primary halo one that hasnt fallen in
  • P-S theory applies only to primary halos
  • Older theory didnt believe in secondary halos
  • Primary/Secondary status changes sign of gas
    accretion/depletion

5
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

6
Characteristic numbers
  • Photo-heating
  • T'104K cs'10 km/s M108M
  • SN heating
  • With Salpeter IMF get 1 SN / 200 M of SF !
    ESN1044J of mechanical E
  • Tmax(mp/200M)ESN/kB3107K

7
Numbers (cont)
  • Gravitational heating
  • Rate of grav heating/unit mass
  • Hgrav(GMH/r2)vG½rv
  • 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 fB0.17
  • Hgrav/Crad Gmp2v0r/fB(T0) r/rcrit where
    rcrit160kpc
  • ! Mcrit' 1012M
  • Bottom line smaller systems never get hot
  • Galaxies dont form by cooling

8
Timeline
  • z'20 small-scale (M106M) 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 (Tlt1K)
  • At z'6 photo heated to 104K
  • Halos less massive than 108 M subsequently cant
    retain gas
  • In low-density regions ! large population
    dark-dark halos?

9
Timeline (contd)
  • At any location scale of halo formation
    increases, as does Tvir
  • Until Tvir106K, M1012M SN-heated gas escapes
  • Until Tvir106K, M1012M infalling gas cold
  • Halos with Mgt1012M acquire hot atmospheres
  • Heating by AGN counteracts radiative cooling
  • Hot gas evaporates limited cold infall !
    quenching of SF

10
Chemical evolution
  • Closed-box model
  • ZMh/Mg (Z0.02)
  • Instantaneous recycling
  • Mh pMs-ZMs (p-Z)Ms
  • Z (Mh/Mg) (Mh-ZMg)/Mg
  • Eliminate Mh ! Z -pln(Mg)
  • ! Z(t)-p lnMg(t)/Mg(0)
  • Ok for gas-rich dwarfs but not dSph!
  • MsltZ(t)Ms(t)Mg(0)-Mg(t)Mg(0)(1-e-Z/p)
  • Ms(ltZ)/Ms(ltZ)(1-x)/(1-x) where xMg(t)/Mg(0)
  • G-dwarf problem with x0.1 Ms(ltZ/4)'0.49Ms but
    only 2 stars lt0.25Z

11
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

12
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)

13
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

14
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
15
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 Tlt106K throughout inner
    cluster

Stewart et al 84
16
G modes
  • Malagoli et al (87)
    overdense regions just crests of gravity
    waves
  • In half a Brunt-Vaisala period theyll be
    underdensities.
  • Oscillations weakly overstable (Balbus Soker
    89) but in reality probably damped.
  • Conclude over timescale lttcool heating must
    balance radiative losses
  • Systems neither cooling nor flowing!

17
2001 Chandra XMM-Newton
  • XMM doesnt see lines of lt106K gas
  • XMM shows that deficit of photons at lt1keV 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)
18
Outward increasing entropy
Omma thesis 05
Donahue 04
19
Summary (cooling flows)
  • Hot atmospheres not thermally unstable will cool
    first _at_ 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 Mgt1012M 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

20
Papers to read
  • Dekel Silk 1986
  • Frenk White 1991
  • Benson et al 2003
  • Cattaneo et al 2006
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