The physics of galaxy formation
Transcript of The physics of galaxy formation
The physics of galaxy formation
P. Monaco, University of Trieste & INAF-OATs
PhD School of Astrophysics Francesco Lucchin
June 2013
LambdaCDM model
Cosmicmicrowavebackground
Large-scale structure
Inter-galactic medium
Galaxy clusters &
gravitational lensing
Distant supernovae
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
Theoretical tools(within the LambdaCDM cosmogony)
Semi-analytic models
N-body + hydrodynamical simulations
Halo Occupation Distribution models
Abundance matching models
The physics of galaxy formation
1. Dark matter
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
Mass function of DM halos
Warren et al. (2006, ApJ 646, 881)
Lacey & Cole (1993, MNRAS 262, 627)
Merger trees
●dynamical friction●tidal stripping●tidal shocks/harrassment●orbit decay (merging)●binary mergers
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
The physics of galaxy formation
1. Dark matter
2. Shock heating and cooling
Gas infall into DM halos
vinfall∼V c=√GM /R
T igm∼103−104K
vinfall≫cs
=> shock heating to the virial T
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
Galaxy clusters show such hot gas
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)
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
z=2, average density 1000 times average
Radiative cooling in presence of UV heating
Radiative cooling of an optically thin plasma: solar abundance ratios
Log T (K)
(1993, ApJS, 88, 253)
metal lines dominate cooling
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
The physics of galaxy formation
1. Dark matter
2. Shock heating and cooling
3. Star formation
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
Cooling below 104 K
Maio et al. (2007, MNRAS 379, 963)
fraction of ions that are metals
Star formation
Kennicutt (1998, ApJ 498, 541)
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
atomic molecular
total
The Kennicutt relation(s) for spirals
Bigiel et al. (2008, AJ 136, 2846)
Two relations at high redshift?
Daddi et al. (2010, ApJ 714, L118)
The physics of galaxy formation
1. Dark matter
2. Shock heating and cooling
3. Star formation
4. Energetic feedback
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
SuperNova Remnant (SNR)
(1) Free expansion
(2) Adiabatic stage
(3) Pressure-driven snowplow stage
(4) Momentum conserving stage
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
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
Feedback in DM halos
thermalenergy
kineticenergy
hot/cold gas metals
Feedback in DM halos
galactic fountain
outflow
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)
A simple energetic argument
ϵE SN M star
M star , SN
=M outflow vSN2
vSN≃√ϵ 750 km /sif
M outflow=M star
The physics of galaxy formation
1. Dark matter
2. Shock heating and cooling
3. Star formation
4. Energetic feedback
5. Morphology
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)
=∣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)
Formation of discs
Dissipation of all random motions
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
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
Galaxy mergers
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
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
Bar instability(secular evolution)
Mergers
pseudo-bulges
bulges/ellipticals
Kormeny & Kennicutt (2004, ARA&A 42, 603)
Morphology at high redshift
Förster Schreiber, N. M., et al. 2009 ApJ, 706, 1364
Problems in galaxy formation
1. Massive galaxies are red and dead
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
...from cooling flow clustersto cool core clusters...
De Grandi & Molendi (2002, ApJ 567, 163)
Massive (cD) elliptical galaxies reside at the centre of galaxy clusters
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
Why are massive ellipticals so old?
(proxy for stellar mass)Nelan et al. (2005, ApJ 632, 137)
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
AGN feedback in action?
Problems in galaxy formation
1. Massive galaxies are red and dead
2. The stellar mass function cuts at ~1011 Msun
Benson et al. (2003, ApJ 599, 38)
The luminosity function
stellar feedback
cooling time + AGN feedback
Constraints from abundance matching
Moster et al. (2010, ApJ 710, 903)
stellar feedbackcooling time + AGN feedback
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
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
Archaeological downsizing
Gallazzi et al. (2005, MNRAS 362, 41)
Downsizing in star formation
Cowie et al. (1996, AJ 112, 839)
Chemo-archaeological downsizing
Trager et al. (2000, AJ 120, 165); Matteucci (1994, A&A 288, 57)
Downsizing in metallicity
Maiolino et al. (2008, A&A 488, 463)
Downsizing in nuclear activity
Brandt & Hasinger (2005, ARA&A 43, 827)
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)
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
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)
“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!
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)
The evolution of star formation rates
Log
aver
age
SFR
of g
alax
ies
(Msu
n yr
-1)
Fontanot et al. (2009)
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
Somerville et al. (2012, MNRAS 423, 1992)
Sub-mm number counts with GALFORM
Baugh et al. (2005, MNRAS 356, 1191)
Sub-mm number counts with MORGANA
with a standard Salpeter IMF
Fontanot et al. (2007, MNRAS 382, 903)
Predicted evolution of Far-IR LF
Lacey et al. (2010, MNRAS 405, 2) Somerville et al. (2012, MNRAS 423, 1992)
Herschel-PEP Far-IR LF
Gruppioni et al. (2013, MNRAS 432, 23)
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
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
The Aquila comparison project
Scannapieco et al. (2012, MNRAS 423, 1726)
A successful simulation of spiral galaxy
Murante et al., in preparation