Galaxy FormationGalaxy Formation

James BinneyJames Binney

Oxford UniversityOxford University

OutlineOutline

• Cosmological clusteringCosmological clustering

• Scales introduced by baryonsScales introduced by baryons

• TimelineTimeline

• Chemical evolution Chemical evolution

• Cores of EsCores of Es

• Cooling flowsCooling flows

CDM BackgroundCDM Background

• Power spectrum of fluctuationsPower spectrum of fluctuations• !! filaments+voids filaments+voids • !! hierarchy of halos hierarchy of halos• Analytic model: Extended Press-Schechter Analytic model: Extended Press-Schechter

theorytheory• characteristic mass(z)characteristic mass(z)• Halo characteristic velocity(M)Halo characteristic velocity(M)• Halo mass fnHalo mass fn• Halo merger probHalo merger prob

Primary & secondary halosPrimary & secondary halos

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

• Survival time tSurvival time tfric fric '' t tdyndyn(M/m)(M/m)

• Primary halo: one that hasn’t fallen inPrimary halo: one that hasn’t fallen in

• P-S theory applies only to primary halosP-S theory applies only to primary halos

• Older theory didn’t believe in secondary Older theory didn’t believe in secondary haloshalos

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

And baryons?And baryons?

• Have e.m. interactions:Have e.m. interactions:• Short-range scatteringShort-range scattering

– adiabatic/shock compressive heatingadiabatic/shock compressive heating• Exchange E with e.m. waves Exchange E with e.m. waves

– emission of bremsstrahlung + line radiation; emission of bremsstrahlung + line radiation; – photo + Compton heatingphoto + Compton heating

• Can form stars and BHs, which heat Can form stars and BHs, which heat surrounding mattersurrounding matter– Mechanically (winds/jets/shocks)Mechanically (winds/jets/shocks)– photonicallyphotonically

Characteristic numbersCharacteristic numbers

• Photo-heatingPhoto-heating– TT''101044K K $$ c css''10 km/s 10 km/s $$ M=10 M=1088MM¯̄

• SN heatingSN heating– With Salpeter IMF get 1 SN / 200 MWith Salpeter IMF get 1 SN / 200 M¯̄ of of

SF SF !! E ESNSN=10=104444J of mechanical EJ of mechanical E

– TTmaxmax=(m=(mpp/200M/200M¯̄)E)ESNSN/k/kBB=3=3££101077KK

Numbers (cont)Numbers (cont)

• Gravitational heatingGravitational heating– Rate of grav heating/unit mass Rate of grav heating/unit mass

• HHgravgrav=(GM=(GMHH/r/r22)v=G)v=G½½rvrv– Rate of radiative cooling/unit massRate of radiative cooling/unit mass

• CCradrad==¤¤(T)n(T)n22/(nm/(nmpp)=)=¤½¤½BB/m/mpp22

• ¤¤(T) = (T) = ¤¤(T(T00)(T/T)(T/T00))1/2 1/2 = = ¤¤(T(T00)v/v)v/v00 with T with T0 0 ' ' 101066K, vK, v0 0 = 100 = 100 km/skm/s

• CCrad rad = = ¤¤(T(T00)f)fBB½½ v/(v v/(v00mmpp22) with f) with fBB=0.17=0.17

– HHgravgrav/C/Crad rad = Gm= Gmpp22vv00r/fr/fBB¤¤(T(T00) = r/r) = r/rcritcrit where r where rcritcrit=160kpc=160kpc

– !! M Mcritcrit'' 10 101212MM¯̄

• Bottom line: smaller systems Bottom line: smaller systems never get hotnever get hot• Galaxies don’t form by coolingGalaxies don’t form by cooling

TimelineTimeline

• zz''20: small-scale (M~1020: small-scale (M~1066MM¯̄) structures begin to collapse) structures begin to collapse• Location: where long & short waves at crests, ie what will be Location: where long & short waves at crests, ie what will be

centres of rich clusterscentres of rich clusters• Voids shepherd matter into filamentsVoids shepherd matter into filaments• Larger & larger regions collapse, driving mergers of Larger & larger regions collapse, driving mergers of

substructuressubstructures• Voids merge tooVoids merge too• A substructures survives if it falls into sufficiently bigger haloA substructures survives if it falls into sufficiently bigger halo• Action spreads from densest to less dense regions Action spreads from densest to less dense regions

(“downsizing”)(“downsizing”)• Initially Universe extremely cold (T<1K)Initially Universe extremely cold (T<1K)• At zAt z''6 photo heated to 106 photo heated to 1044KK• Halos less massive than 10Halos less massive than 1088 M M¯̄ subsequently can’t retain gas subsequently can’t retain gas• In low-density regions In low-density regions !! large population dark-dark halos? large population dark-dark halos?

Timeline (contd)Timeline (contd)

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

• Until TUntil Tvirvir=10=1066K, M=10K, M=101212MM¯̄ SN-heated gas SN-heated gas escapesescapes

• Until TUntil Tvirvir=10=1066K, M=10K, M=101212MM¯̄ infalling gas cold infalling gas cold• Halos with M>10Halos with M>101212MM¯̄ acquire hot atmospheres acquire hot atmospheres• Heating by AGN counteracts radiative coolingHeating by AGN counteracts radiative cooling• Hot gas evaporates limited cold infall Hot gas evaporates limited cold infall !!

“quenching” of SF“quenching” of SF

Chemical evolution Chemical evolution

• Closed-box modelClosed-box model• Z=MZ=Mhh/M/Mgg (Z (Z¯̄=0.02)=0.02)• Instantaneous recyclingInstantaneous recycling• ±±MMh h = p= p±±MMss-Z-Z±±MMs s = (p-Z)= (p-Z)±±MMss

• ±±Z = Z = ±±(M(Mhh/M/Mgg) = () = (±±MMhh-Z-Z±±MMgg)/M)/Mgg

• Eliminate Eliminate ±±MMhh !! ±± Z = -p Z = -p±±ln(Mln(Mgg))• !! Z(t)=-p ln[M Z(t)=-p ln[Mgg(t)/M(t)/Mgg(0)](0)]• Ok for gas-rich dwarfs but not dSph!Ok for gas-rich dwarfs but not dSph!• MMss[<Z(t)]=M[<Z(t)]=Mss(t)=M(t)=Mgg(0)-M(0)-Mgg(t)=M(t)=Mgg(0)(1-e(0)(1-e-Z/p-Z/p))• MMss(<(<®®Z)/MZ)/Mss(<Z)=(1-x(<Z)=(1-x®®)/(1-x) where x=M)/(1-x) where x=Mgg(t)/M(t)/Mgg(0)(0)• G-dwarf problem: with x=0.1 MG-dwarf problem: with x=0.1 Mss(<Z(<Z¯̄/4)/4)''0.49M0.49Mss but but

only 2% stars <0.25Zonly 2% stars <0.25Z¯̄

In or out?In or out?

• The box is open!The box is open!• Outflow or inflow?Outflow or inflow?• Arguments for inflow: Arguments for inflow:

– SFR SFR '' const in solar nhd (Hipparcos) const in solar nhd (Hipparcos)– S0 galaxies are spirals that have ceased SF (TF relation S0 galaxies are spirals that have ceased SF (TF relation

& specific GC frequency); they are also in locations & specific GC frequency); they are also in locations where we expect inflow to have been reversed where we expect inflow to have been reversed (Bedregal et al 2007)(Bedregal et al 2007)

• Arguments for outflow:Arguments for outflow:– in rich clusters ~half of heavy elements are in IGMin rich clusters ~half of heavy elements are in IGM– in M82 you see ouflow (probably in Galaxy too)in M82 you see ouflow (probably in Galaxy too)– application of leaky box to globular-cluster systemapplication of leaky box to globular-cluster system

Leaky-box modelLeaky-box model

• dMdMtt/dt=-c dM/dt=-c dMss/dt/dt

• !!

• Can also apply to centres of ellipticals Can also apply to centres of ellipticals with c(with c(¾¾) by equating E of ejection to ) by equating E of ejection to EESNSN (S5.3.2 of Binney & Merrifield) (S5.3.2 of Binney & Merrifield)

M s(< Z) =M t(0)1+ c

³1¡ e¡ (1+c)Z=p

´

®® enhancement enhancement

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

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

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

• Implies SF complete inside 1GyrImplies SF complete inside 1Gyr

Centres of EsCentres of Es

• Photometry of Es fitted byPhotometry of Es fitted by

§ (R) =1

R° (a+ R)¯ ¡ °

Lauer + 07

Nipoti & Binney 07

Conclude: on dry merging cores destroyed by BHs; in gas-rich mergers reformed by SF

Cooling flows: mass dropoutCooling flows: mass dropout• In 1980s & 90s X-ray profiles interpreted on In 1980s & 90s X-ray profiles interpreted on

assumption that (i) steady-state, (ii) no assumption that (i) steady-state, (ii) no heatingheating

• Imply diminishing flow to centreImply diminishing flow to centre• ICM multiphase (Nulsen 86)ICM multiphase (Nulsen 86)• Field instability analysis implied runaway Field instability analysis implied runaway

cooling of overdense regions (tcooling of overdense regions (tcoolcool// 1/ 1/))• Cooler regions radiate all E while at rCooler regions radiate all E while at rÀÀ 0 0• Predicts that there should be (a) cold gas and Predicts that there should be (a) cold gas and

(b) line radiation from T<10(b) line radiation from T<1066K throughout K throughout inner clusterinner cluster

Stewart et al 84

G modesG modes

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

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

• Oscillations weakly overstable (Oscillations weakly overstable (Balbus & Soker Balbus & Soker 8989) but in reality probably damped.) but in reality probably damped.

• Conclude: over timescale <tConclude: over timescale <tcoolcool heating must heating must balance radiative lossesbalance radiative losses

• Systems neither cooling nor flowing!Systems neither cooling nor flowing!

2001 – Chandra & XMM-2001 – Chandra & XMM-NewtonNewton

• XMM doesn’t see lines of <10XMM doesn’t see lines of <1066K gasK gas

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

• But associated with “floor” TBut associated with “floor” T'' T Tvirvir/3/3

• Chandra shows that radio plasma has Chandra shows that radio plasma has displaced thermal plasmadisplaced thermal plasma

(Bohringer et al 02)

(Peterson et al 02)

Outward increasing entropyOutward increasing entropy

Omma thesis 05

Donahue 04

Summary (cooling flows)Summary (cooling flows)

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

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

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

• Result: halos M>10Result: halos M>101212MM¯̄ have little SF have little SF• Smaller halos that fall into such big halos Smaller halos that fall into such big halos

gradually sterilized by ablation toogradually sterilized by ablation too• Hence decline in cosmic SF rate at current Hence decline in cosmic SF rate at current

epochepoch

Papers to readPapers to read

• Dekel & Silk 1986Dekel & Silk 1986

• Frenk & White 1991Frenk & White 1991

• Benson et al 2003Benson et al 2003

• Cattaneo et al 2006Cattaneo et al 2006