The physics of galaxy formation
Transcript of The physics of galaxy formation
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The physics of galaxy formation
P. Monaco, University of Trieste & INAF-OATs
PhD School of Astrophysics Francesco Lucchin
June 2013
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LambdaCDM model
Cosmicmicrowavebackground
Large-scale structure
Inter-galactic medium
Galaxy clusters &
gravitational lensing
Distant supernovae
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Cosmology
gravitational
collapse
Galaxies
“gastrophysics”
z=5.7 (t=1.0 Gyr)z=5.7 (t=1.0 Gyr)
z=1.4 (t=4.7 Gyr)z=1.4 (t=4.7 Gyr)
z=0 (t=13.6 Gyr)z=0 (t=13.6 Gyr)
Springel et al. 2006Springel et al. 2006
Dark matter
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Theoretical tools(within the LambdaCDM cosmogony)
Semi-analytic models
N-body + hydrodynamical simulations
Halo Occupation Distribution models
Abundance matching models
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The physics of galaxy formation
1. Dark matter
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ρ(r )=ρc (z)const
cx(1+cx)2
c≡rhr s, x≡ r
rh, cx= r
r sρ(rh)=200ρc (z )
Density profile:Navarro, Frenk & White (1997, ApJ 490, 493)
Dark-matter halos
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Mass function of DM halos
Warren et al. (2006, ApJ 646, 881)
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Lacey & Cole (1993, MNRAS 262, 627)
Merger trees
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●dynamical friction●tidal stripping●tidal shocks/harrassment●orbit decay (merging)●binary mergers
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Dynamicalfriction
ddtvorb=
−4G 2 ln M sat host v orbv orbvorb
3
tmerge=1.17f dfln
orb
M host
M sat
Boylan-Kolchin, Ma & Quataert (2008, MNRAS, 383, 93)
Coulomb logarithm
Parameter Orbital parameter
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The physics of galaxy formation
1. Dark matter
2. Shock heating and cooling
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Gas infall into DM halos
vinfall∼V c=√GM /R
T igm∼103−104K
vinfall≫cs
=> shock heating to the virial T
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Massive halos (>1012 Msun
):cooling is slower than infallgas is shock- heated at T
vir
and is in roughly hydrostatic equilibrium
Small halos (<1011 Msun
):cooling is faster than infallcold gas falls directly to the centrethe shock energy is quickly dissipated
White & Frenk (1991, ApJ 379, 52), Keres et al. (2005, MNRAS 363, 2), Dekel & Birnboim (2006, MNRAS 368, 2)
Shock heating and cold flows
t coolt dyn t coolt dyn
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Galaxy clusters show such hot gas
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Hot baryons in DM halos
NFW profile for the total mass
halo concentration
hydrostatic equilibrium
polytropic equation of state (γp~1.2)
solution for the density
=crit c
r / r s1r /r s2
c=r h/r s
dPg
dr=−G
g M r r 2
P g∝g p
g r =g0 [1−a1− ln 1r /r sr /r s ]
1/ p−1
a=aT g0 /T vir , p , cKomatsu & Seljak (2001, MNRAS 327, 1353)
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Radiative cooling of an optically thin plasma: primordial composition
log T (K)
L=n ine , T
t cool=∣d lnTdt ∣
−1
=E th
L= 3nkT
2ne ni
Katz, Weinberg & Hernquist (1996, ApJS, 105, 19)
Assumptions:● collisional ionisation equilibrium● thermal distribution of e- and ions● no external ionising radiation
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z=2, average density 1000 times average
Radiative cooling in presence of UV heating
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Radiative cooling of an optically thin plasma: solar abundance ratios
Log T (K)
(1993, ApJS, 88, 253)
metal lines dominate cooling
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The "classical" cooling model in SAMs
The cooling radius:
Bertschinger's (1989) self-similar solutions:
The "classical" cooling model (White & Frenk 1991):
Total cooling time of a mass element:
The classical model implies that:
r cool t : t cool r =t
M cool∝4g r cool r cool2 dr cool
dt
M cool=4 g rcool r cool2 drcool
dt
t total :T t total≪T t=0
t cool r =t total r
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The physics of galaxy formation
1. Dark matter
2. Shock heating and cooling
3. Star formation
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Star formation and Jeans mass
E tot = U+Ω = 32kT
M J
μm p
−GM J
2
R=0
M J∼15.4( T1 K )3/2
( n
1 cm−3 )−1 /2
M sun
Warm phase
Cold phase
Molecular phase
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Cooling below 104 K
Maio et al. (2007, MNRAS 379, 963)
fraction of ions that are metals
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Star formation
Kennicutt (1998, ApJ 498, 541)
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DATA:
THINGS (VLA): 21 cm -> HI
BIMA-SONG + HERACLES: CO → H2
SINGS (Spitzer): 24 μm
GALEX: UV
24 μm + UV -> SFR
resolution: 750 pc, 5.2 km/s
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atomic molecular
total
The Kennicutt relation(s) for spirals
Bigiel et al. (2008, AJ 136, 2846)
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Two relations at high redshift?
Daddi et al. (2010, ApJ 714, L118)
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The physics of galaxy formation
1. Dark matter
2. Shock heating and cooling
3. Star formation
4. Energetic feedback
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Feedback sources
Supernova explosions
UV from massive stars
Star winds
AGN
1051 erg each >8 Msun
star + type Iaup to ~1050 erg
each >10 Msun
star
up to ~1050 erg each >10 M
sun star
up to ~1047 erg s-1 for ~107 yr
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SuperNova Remnant (SNR)
(1) Free expansion
(2) Adiabatic stage
(3) Pressure-driven snowplow stage
(4) Momentum conserving stage
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SN energy feedback
Energy is injected through blastwaves
The ISM is heated in the adiabatic stage
The ISM is cooled if the blast goes into the “snowplough” stage
McKee & Ostriker 1977Cioffi, McKee & Berschinger 1988Ostriker & McKee 1988
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The efficiency of feedback
It is determined by the energy radiated away before the blast stops propagating.
Blasts stop by:
merging with the ISM
blowing out of the galaxy
merging with other blasts
v s=cs0
R s=H eff
Q bubbles=1
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Feedback in DM halos
thermalenergy
kineticenergy
hot/cold gas metals
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Feedback in DM halos
galactic fountain
outflow
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Simple model of feedback
The properties of dwarf galaxies require that gas is efficiently removed from small halos.
Condition for removal:
Energy from (tII) SNe:
Star formation:
Critical Vc:
E inj=ϵ E aval≥M gasV c2
(Dekel & Silk 1986)
Eaval=E SN SN M star
M star=M gas / t ff
V c≈100km /sParameters: E
SN ( E
51), η
SN (IMF), ε, τ (computed)
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A simple energetic argument
ϵE SN M star
M star , SN
=M outflow vSN2
vSN≃√ϵ 750 km /sif
M outflow=M star
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The physics of galaxy formation
1. Dark matter
2. Shock heating and cooling
3. Star formation
4. Energetic feedback
5. Morphology
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Angular momentum of halos
J = ∫V L
a3ax−a xcm ×v d3 x
J i= −a D ijk T jl I lk ∝ t1 /3M 5 /3
tidal tensor inertia tensorWhite (1984, ApJ 286, 38)
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=∣E∣1 /2∣ J h∣
G M h5/2 ≃
V rot
V c
V c= GM h
r h
Spin parameter
Bett et al. (2007, MNRAS, 376 215)
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Formation of discs
Dissipation of all random motions
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The size of discs
Assuming that(1) a fraction m
d of the halo baryonic mass settles on the disc
(2) a fraction jd of the angular momentum is conserved
(3) the disc has an exponential profile(4) the disc has negligible mass
(5) the halo has a singular isothermal profile
Rd =G M h
3/2
2Vc∣E∣1/2 j dmd
Rd =1
2 j dmd r h
Mo, Mao & White (1998, MNRAS 295, 319)
r=0 exp − rRd
r∝r−2
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Complications
(1) NFW halo
(2) disc mass not negligible
(3) adiabatic contraction of the DM halo
(4) central bulge
iterative solution!
GM r r=const
J d
M d
= j dmd J h
M h
J d = ∫0
rhV rot r rr 2 r dr
V rot2 =V dm
2 V d2V b
2
V d2=
G M d
Rd
y2 [ I 0 y K 0 y− I 1 y K 1 y ] , y= 12rRd
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Galaxy mergers
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Bar instabilityThin discs are unstable to bar formation, unless they are surrounded by a DM halo (Ostriker & Peebles 1973)
≡V d Rd
G M d
limit~1
limit :
Stability condition:
(Efstathiou et al. 1982, Christodoudou et al. 1995)
disc is unstable to m=2 modes
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Disc instability
Bournaud et al. (2008, A&A 486, 741)
2r=2V d2
r 2 V d
r
dV d
dr if V d~V c then ~2
V c
r
Q r≡cs
G gas
Q1 : disc is unstable to axisymmetric modes
Toomre criterion for a gas disc
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Bar instability(secular evolution)
Mergers
pseudo-bulges
bulges/ellipticals
Kormeny & Kennicutt (2004, ARA&A 42, 603)
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Morphology at high redshift
Förster Schreiber, N. M., et al. 2009 ApJ, 706, 1364
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Problems in galaxy formation
1. Massive galaxies are red and dead
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A problem with cooling flowsin Galaxy Clusters
Peterson & Fabian (2006)
X-ray observations of galaxy clusters allow us to estimate density and temperature, and then cooling time, of the hot gas.
Some clusters should be sites of strong cooling flows
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...from cooling flow clustersto cool core clusters...
De Grandi & Molendi (2002, ApJ 567, 163)
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Massive (cD) elliptical galaxies reside at the centre of galaxy clusters
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Brinchmann et al. (2004, MNRAS 351, 1151)
Why are massive galaxies red & dead? sp
eci
fic s
tar
form
atio
n ra
te
stellar mass
The mass deposited into the galaxy is 10-1 or 10-2 times that suggested by the cooling flow
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Why are massive ellipticals so old?
(proxy for stellar mass)Nelan et al. (2005, ApJ 632, 137)
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A possible answer: AGN feedback
(proxy for stellar mass)
Every elliptical galaxy hosts a super-massive black hole at its centre
These black holes may be reactivated by the cooling gas
Ferrarese & Merritt 2000Gebhardt et al. 2000
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AGN feedback in action?
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Problems in galaxy formation
1. Massive galaxies are red and dead
2. The stellar mass function cuts at ~1011 Msun
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Benson et al. (2003, ApJ 599, 38)
The luminosity function
stellar feedback
cooling time + AGN feedback
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Constraints from abundance matching
Moster et al. (2010, ApJ 710, 903)
stellar feedbackcooling time + AGN feedback
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Problems in galaxy formation
1. Massive galaxies are red and dead
2. The stellar mass function cuts at ~1011 Msun
3. Galaxies show several “downsizing” trends
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The many manifestations of downsizing: Fontanot et al. (2009, MNRAS 397, 1176)
archaeological DS more massive galaxies host older stellar populations
star formation DS:the mass of the typical SF galaxy grows with z
stellar mass DS:at z≲1 the number density of smaller galaxies evolves faster
chemical DS:the metallicity of smaller galaxies evolves faster
chemo-archaeological DS:more massive ellipticals have higher [α/Fe] ratios
AGN DS:the number density of fainter AGN peaks at lower z
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Archaeological downsizing
Gallazzi et al. (2005, MNRAS 362, 41)
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Downsizing in star formation
Cowie et al. (1996, AJ 112, 839)
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Chemo-archaeological downsizing
Trager et al. (2000, AJ 120, 165); Matteucci (1994, A&A 288, 57)
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Downsizing in metallicity
Maiolino et al. (2008, A&A 488, 463)
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Downsizing in nuclear activity
Brandt & Hasinger (2005, ARA&A 43, 827)
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comparison of three models:Garching-De LuciaMorganaSomerville 08
(assumed error on mass: 0.25 dex)with observational estimates of stellar mass functions by
Panter+ 07, SDSSCole+ 01, 2MASSBell+ 03, 2MASS+SDSSBorch+ 06, COMBO17 PerezGonzalez+ 08, SpitzerBundy+ 06, DEEP2Drory+ 04, MUNICSDrory+ 05, FDF+GOODSFontana+ 06, GOODS-MUSICPozzetti+ 07, VVDSMarchesini+ 08, 3 samples
Stellar mass function
Fontanot et al. (2009)
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10
-10
.5
10
.5-1
1
11-
11.5
11.5
-12
in L
og M
*
Log
Ste
llar
mas
s de
nsity
(M
sun M
pc-3)
Downsizing in stellar mass
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first best-fit model
second best-fit model
Redshift intervals:3.4 < z < 4.5 (B-drop)
4.5 < z < 5.5 (V-drop)
5.5 < z < 6.5 (i-drop)
Lyman-break galaxies in a SAM
B-drop
i-drop
V-drop
Lo Faro et al. (2009, A&A 399, 827)
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“Excess” galaxies
absolute UV magnitude: MUV
~-18
star formation rate: SFR~10 Msun
yr-1
apparent magnitude: z850
~27
stellar mass: M*~108-109 M
sun@z~6 to 109-1010 M
sun@z~4
bimodal metallicity: Z~solar and Z~0.25 solarhosted in halos of: M
h~1011-1012 M
sun
with circular velocities: Vc~120-250 km/s
Important contributors to the IGM pollution
Waiting for ALMA and JWST!
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Problems in galaxy formation
1. Massive galaxies are red and dead
2. The stellar mass function cuts at ~1011 Msun
3. Galaxies show several “downsizing” trends
4. Growth of average SFR with z (Daddi)
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The evolution of star formation rates
Log
aver
age
SFR
of g
alax
ies
(Msu
n yr
-1)
Fontanot et al. (2009)
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Problems in galaxy formation
1. Massive galaxies are red and dead
2. The stellar mass function cuts at ~1011 Msun
3. Galaxies show several “downsizing” trends
4. Growth of average SFR with z (Daddi)
5. Surprises from the cool side of galaxies
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Somerville et al. (2012, MNRAS 423, 1992)
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Sub-mm number counts with GALFORM
Baugh et al. (2005, MNRAS 356, 1191)
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Sub-mm number counts with MORGANA
with a standard Salpeter IMF
Fontanot et al. (2007, MNRAS 382, 903)
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Predicted evolution of Far-IR LF
Lacey et al. (2010, MNRAS 405, 2) Somerville et al. (2012, MNRAS 423, 1992)
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Herschel-PEP Far-IR LF
Gruppioni et al. (2013, MNRAS 432, 23)
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Problems in galaxy formation
1. Massive galaxies are red and dead
2. The stellar mass function cuts at ~1011 Msun
3. Galaxies show several “downsizing” trends
4. Growth of average SFR with z (Daddi)
5. Surprises from the cool side of galaxies
6. Angular momentum loss in hydro simulations
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bottom-up formation of DM halo+
overcooling (White & Rees 1978, MNRAS 183, 341)
+segregation of cooled baryons
+dynamical friction and tidal stripping
=angular momentum loss
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The Aquila comparison project
Scannapieco et al. (2012, MNRAS 423, 1726)
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A successful simulation of spiral galaxy
Murante et al., in preparation
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