Formation of the Galaxies: Current Issues Joe Silk University of Oxford Gainesville, October 2006.
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Transcript of Formation of the Galaxies: Current Issues Joe Silk University of Oxford Gainesville, October 2006.
Formation of the Galaxies:
Current Issues
€
Joe Silk
University of Oxford
Gainesville, October 2006
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
THE INITIAL STELLAR MASS FUNCTION What determines the characteristic
mass of a star?
Is the IMF universal?
Kroupa 2004Kroupa 2004
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
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˙ M gas ~vs
3
G⇒
3 PROCESSES PLAY A ROLE:FRAGMENTATION, ACCRETION, FEEDBACK
Shu 2006
NGC1333: Quillen et al. 2006
Pudritz et al. 2006Shu 2006
Klessen 2006
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
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~
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Mcooled −baryons ~ α g−2α 3 mp
me
⎛
⎝ ⎜
⎞
⎠ ⎟tcool
tdyn
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟T
1+2β
So the BIG ISSUE is astrophysical feedback
€
β ~ −0.5
Ultraluminous infrared galaxies and the galaxy luminosity function
Sanders 1999
The red sequence evolves
Bell et al. 2004 Blanton 2006
Star formation was efficient in the most massive galaxies
Papovich et al. 2006
More evidence for a shorter timescale
Maraston 2006
AN EFFICIENT MODE OF STAR FORMATION IS NEEDED FOR SPHEROID FORMATION: THE CASE FOR POSITIVE FEEDBACK
D. Thomas
D. Thomas 2006
DISK MODE: motivated by gravitational instability of cold disksstar surface densitygas surface density
SFE = gas
vcool m*,SN
ESN initial
0.02
€
σ
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≈
Star formation efficiency
THERE ARE PLAUSIBLY TWO MODES OF STAR FORMATION: REGULATED BY GAS SUPPLY, DYNAMICAL TIMESCALE ….
SPHEROID MODE: motivated by gas-rich mergers
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
NGC 891
HI contours
Oosterloo et al. 2005Boomsma et al 2005
NGC 6946
LOCAL COLD GAS FEEDING BY INFALL
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!
SFR with SN feedback in a multiphase ISM
Slyz et al. (2005)
HISTORY OF STAR FORMATION
Rocha-Pinto 2000: solar vicinity
Allard et al. 2006: M100
Star Formation Rate Simulation
The Mice (NGC 4676 a,b)old stars + gasdensity-dependent SFR shock-induced SFR
Barnes (2004)
Bower et al. 2006
space density of galaxies
GALAXY LUMINOSITY FUNCTION
AGN Feedback
luminosity
Massive spheroids form first
K. Bundy et al. 2006
Cimatti et al. 2006
Bouwens, Illingworth et al 2006
Build-up of luminosity and star formation rate
AGN ARE ANTI-HIERARCHICAL
Hasinger et al. 2006
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
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
star formation rate compared to renormalised black hole feeding rate
Silverman et al. 2006
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
at z~2, SMBH fall below the relation
Star formation suppressed
Star formation triggered
Borys et al 2006
€
˙ 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
OUTFLOWS FROM ULIRGSC. Martin 2005: KI and NaI line profiles
Morganti et al. 2005: HI absorption
Swinbank et al. 2006 a SCUBA galaxy at
z=2.385
multiplicative factor of AGN-triggered SN
Everett & Murray 2006:
extended injectionof energy needed for NGC 4151 outflow
X-ray absorbed QSOs in ULIRGs
Ultraluminous starburstsassociated with AGN absorptionby ionised wind
M. Page et al. 2006
A UNIFIED THEORY
NEGATIVE
POSITIVE
FRESH THEORETICAL INGREDIENTS ARE NEEDED!