formation of the galaxies: current issues joe silk university of oxford gainesville, october 2006
TRANSCRIPT
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Formation of the Galaxies:
Current Issues
€
Joe Silk
University of Oxford
Gainesville, October 2006
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Some remarks about star formation…mass, light, chemistry control galaxy evolution Low mass stars control M
Solar mass stars control light in a spheroidal galaxy
The most massive stars dominate the light in a disk galaxy
Intermediate mass stars control chemical evolution
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THE INITIAL STELLAR MASS FUNCTION What determines the characteristic
mass of a star?
Is the IMF universal?
Kroupa 2004Kroupa 2004
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Stars
Fundamental theory applied to a diffuse interstellar cloud that is collapsing under self-gravity
Minimum fragment mass
a robust but wrong result! Resolution: continuing accretion of cold gas, eventually halted by feedback that taps stellar energy via MHD turbulence
first stars were massive
In addition IMF most likely also involves fragmentation
M 01.0~~ 2/3pg m−α
€
˙ M gas ~vs
3
G⇒
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3 PROCESSES PLAY A ROLE:FRAGMENTATION, ACCRETION, FEEDBACK
Shu 2006
NGC1333: Quillen et al. 2006
Pudritz et al. 2006Shu 2006
Klessen 2006
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Ellipticals are old because infall is quenched….by AGN outflowsEfficient early star formation occurred in massive spheroids and ellipticals
There are likely to be two modes of star formation: disks/pseudobulges AND elliptical/spheroid formation
Disk galaxy star formation is inefficient, due to SN feedback Accretion and minor mergers renew gas supply
Accretion, mergers and AGN outflows are key ingredients
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Galaxies
Gas cooling time-scale
Dynamical time-scale
A necessary condition for star formation is cooling:
)(Lφ
luminosity
theory (CDM-motivated)
observations
LL 10103~ ×∗
too many Dwarfsbut they are fragile
too many Giants:a problem!
2)(~
nT
nkTtcool Λ
nGmt
p
dyn
1~
€
Mcooled −baryons ~ α g−2α 3 mp
me
⎛
⎝ ⎜
⎞
⎠ ⎟tcool
tdyn
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟T
1+2β
So the BIG ISSUE is astrophysical feedback
€
β ~ −0.5
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Ultraluminous infrared galaxies and the galaxy luminosity function
Sanders 1999
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The red sequence evolves
Bell et al. 2004 Blanton 2006
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Star formation was efficient in the most massive galaxies
Papovich et al. 2006
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More evidence for a shorter timescale
Maraston 2006
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AN EFFICIENT MODE OF STAR FORMATION IS NEEDED FOR SPHEROID FORMATION: THE CASE FOR POSITIVE FEEDBACK
D. Thomas
D. Thomas 2006
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DISK MODE: motivated by gravitational instability of cold disksstar surface densitygas surface density
SFE = gas
vcool m*,SN
ESN initial
0.02
€
σ
€
≈
Star formation efficiency
THERE ARE PLAUSIBLY TWO MODES OF STAR FORMATION: REGULATED BY GAS SUPPLY, DYNAMICAL TIMESCALE ….
SPHEROID MODE: motivated by gas-rich mergers
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A GLOBAL STAR FORMATION LAW FOR DISKS
Need cold gas accretion via infall and/or minor mergersto maintain global disk instabilityNeed low efficiency: due to SN feedback
SFR=0.02 (GAS SURFACE DENSITY)/tdyn
Sajina et al. 2006
fits quiescent and starburst galaxies
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NGC 891
HI contours
Oosterloo et al. 2005Boomsma et al 2005
NGC 6946
LOCAL COLD GAS FEEDING BY INFALL
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The Rate of Star Formation
( ) ⎟⎟⎠
⎞⎜⎜⎝
⎛×
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛×
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛
1.36(pressure)
1rateformation star ~
pressure ISMambient
by limited bubble a of
Volume-4 maximum
unit timeper
generated
bubbles SN
ofnumber
~porosity
Three-phase ISM
Perhaps porosity self-regulates!
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SFR with SN feedback in a multiphase ISM
Slyz et al. (2005)
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HISTORY OF STAR FORMATION
Rocha-Pinto 2000: solar vicinity
Allard et al. 2006: M100
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Star Formation Rate Simulation
The Mice (NGC 4676 a,b)old stars + gasdensity-dependent SFR shock-induced SFR
Barnes (2004)
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Bower et al. 2006
space density of galaxies
GALAXY LUMINOSITY FUNCTION
AGN Feedback
luminosity
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Massive spheroids form first
K. Bundy et al. 2006
Cimatti et al. 2006
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Bouwens, Illingworth et al 2006
Build-up of luminosity and star formation rate
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AGN ARE ANTI-HIERARCHICAL
Hasinger et al. 2006
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SMBH formation/feedback in galaxy spheroid formation
Fits observed normalisation and slope
King (2003), Silk & Rees (1998)
Supernovae provide feedback in potential wells of low mass galaxies SMBH outflows provide positive
feedback in massive protospheroids Blowout occurs/star formation
terminates when SMBH- relation is saturated
€
M• = 3 ×109 Msun σ
300 km
s
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
4
€
€
σ
LEdd/c=GMMgas/r2
LEddMSMBH
black holemass
spheroid velocity
dispersion
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Triggered global star formation? OUTFLOWS
FROM SMBH OVERPRESSURE ISM CLOUDS star formation timescale tjet<<tgal
yields high efficiency
Labiano et al. 2005z=0.27 radio galaxy
Saxton et al. 2005
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star formation rate compared to renormalised black hole feeding rate
Silverman et al. 2006
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jet-enhanced star formation in spheroids
redshift
comoving star formation rate
comoving SMBH accretion rate
x 10-3
suppressionby ouflows
gravity-induced star formation
feedback
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at z~2, SMBH fall below the relation
Star formation suppressed
Star formation triggered
Borys et al 2006
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€
˙ M sfrAGN = ˙ M sfr
SN (tdyn / t jet )
≈ εMgas(v jet /σ ) / tdyn ∝ vw3
AGN-induced outflows & star formation
Boost by ~10! Observed scaling!
€
˙ M gasoutflowAGN ~ LAGN /cvw ∝σ 3
˙ M gasoutflowSN ∝ ˙ M sfrσ
−2.7
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OUTFLOWS FROM ULIRGSC. Martin 2005: KI and NaI line profiles
Morganti et al. 2005: HI absorption
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Swinbank et al. 2006 a SCUBA galaxy at
z=2.385
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multiplicative factor of AGN-triggered SN
Everett & Murray 2006:
extended injectionof energy needed for NGC 4151 outflow
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X-ray absorbed QSOs in ULIRGs
Ultraluminous starburstsassociated with AGN absorptionby ionised wind
M. Page et al. 2006
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A UNIFIED THEORY
NEGATIVE
POSITIVE
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FRESH THEORETICAL INGREDIENTS ARE NEEDED!