Galaxy Formation

1
Galaxy Formation

• James Binney
• Oxford University

TexPoint fonts used in EMF. Read the TexPoint
manual before you delete this box. AAAAAAA
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