m *
high
m*
High-mass
Low-mass galaxies
Athigh
high-redshift,
cold gas
At
z>2, SF proceeds
at
extremely
high
rates by feedback
effectively
expelled
Suppressed
at high in
–z
Feedback
is SF
ineffective
suppressing star formation
At lower z, haloes grow and
feedback
less effective
Rapid
gas becomes
consumption
m *
low
m*
Coldgas
gasexhausting
left available
at low-z
Cold
at z~2
Starformation
formationdrops
still active
at low
Star
thereafter
Smooth
SF history
Local
galaxies
are gas poor with
old stars
large mass
small mass
Observations show:
A sharp transition in the physical properties of galaxies at
M* ~ 3 1010 Mʘ (see, e.g., Kauffmann et al. 2003)
Tully, Mould, Aaronson 1982
• Massive galaxies are redder
• Contain older stars
• star formation much larger at high
redshitfs
Bimodal Color Distribution
Bright
Red Galaxies
Faint
Blue Galaxies
Baldry et al. 2004
Color Distribution Dependence on luminosity
BLUE
RED
The cold gas fraction
log Number
log Number
Local galaxies with u-r<1
-20.5 < Mr <-19.5
Local galaxies with u-r>1.5
vc2 feedback   0 ESN  100 km / s
M=109 Mʘ at z=4.5
Mprog=109 Mʘ
Colore Distribution: Dependence on the environment
t1
t2
small mass
halo
t3
Large mass
halo
Z=0
Galaxies endng up in clusters
originate from the merging of
clumps which have collapsed in
biased, high-density regions of the
density field, hence at higher
redshift.
The star formation histories
of the population contained (today)
in dense environments
(groups/clusters)
peaks at higher redshift
compared to that of smaller galaxies.
Bimodality extends at least up to z ≈ 0.8
Bell et al. 03
The Evolution of luminosity and mass functions
i) density evolution, typical of hierarchical clustering
clustering,
(mass of galaxies increases with time)
ii) luminosity evolution
(SFR increasing with z from z=1 to z=2.5, flat at higher z)
estimates from
Glazebrook et al. (GDDS)
Rudnick et al. (FIRES)
Dickinson et al. (HDFN)
Fontana et al. (K20)
Bell et al. (COMBO)
The Luminosity Evolution
I:Luminosity evolution:
B and UV
- B-band and UV luminosity ~
instanteneous star form. rate
- The number of massive objects
decreases with z
(hierarchical clustering)
- Star Formation strongly increases
with z
N
Z=3
Z=0
*
LB 
Mm
II: Luminosity
evolution: K
MZ<25
- K-band luminosity ~ total mass
in stars formed at current time
At z ~ 1.5 simple models
underpredict the total amount
of stars formed in massive
haloes
Additional mechanism MUST
BE triggering
star formation at z≥4
t
Starbursts
S    m * (t  t ' )   (t ' ) dt '
Pozzetti et al. 2003
0
t
  (t ' )  const  S    m * (t  t ' ) dt '  m*
0
Data: Fontana et al
‘”tidal forces during encounters
cause otherwise stable disks to
develop bars, and the gas in such
barred disks, subjected to strong
gravitational torques, flows toward
the central regions “
Mihos & Hernquist 1996
See also Noguchi 1987
Barnes & Hernquist 1991
Gas Angular Momentum
Part of the available galactic cold gas is detabilized and
funnelled toward the centre
Cavaliere
1 j 1 m' rd vd
Vittorini
f ( v, V ) 

2000
2 j
2 mbV
Rate:
2
 1  n ( rtidal
) Vrel
FlyBy
Duration: 1
 r  Vrel / rtidal
Part of the available cold gas is detabilized and funnelled toward the centre
1 j 1 m' rd vd
f ( v, V ) 

2 j
2 mbV
Cavaliere
Vittorini
2000
(Sanders & Mirabel 96)
Starbursts Freqency
Starbursts Mass Conversion rate
2
 1  n ( rtidal
) Vrel
FlyBy
Strongly increases with z
2
FlyBy
3
4
f mcold
n  1 / R3
Strongly increases with z
2
larger m’/m ratios
 r  Vrel  r  1
    dyn
R R R
 1   
 * ( v, t ) 
m
Larger vd/V ratio
Larger r/R ratio
Smaller r~(1+z)-1/2
Smaller r~(1+z)-1/2
Larger cold gas mass
r
Larger
f ≥ 0.01
The Bursts
EROs
AGN activity triggered by
destabilization of gas during
encounters:
Would naturally explain
1) They are already in place at high z
(at least at z=2, see McLure talk)
while the stellar content of galaxies
is still growing
II) Their activity drops at lower z
Burst constitute only one mode of star formation
addig to quiescent star formation
BUT for AGN constitute the whole feeding mechanism
The effect of Starbursts on the Galaxy Lum. Function.
Cold Gas destabilization
from Fly-by interactions
strongly decreases from
z=3 to z=0
Somerville Primack & Faber 2001
At high z a large amount of
cold gas is destabilized
Strong starbursts are
expected at z > 3-4
MZ < 25.5
L > 0.2 L*
Data from Giavalisco et al. 03
The effect of Starbursts
induced by fly-by events in
the K-band observables
NM et al 2004
K-band z-counts
K-band Lumin. Functions
Stellar Mass function at high z
z=1-1.6
z=1.6-2
z=2-3
The Big Picture
At z > 2.5 – 3
-Effective cooling (low virial T≈105 K, high densities)
-rapid merging, frequent encounters allow continuous refueling of gas in the growing galactic haloes.
Large B/ UV
-High SFR (≈102 Mʘ/yr), especially in clumps formed in BIASED regions of the density field
Emission
(progenitors of large-mass galaxies / cluster members.
Ly-break glxs
9
-Self-regulated SF: in small-mass clumps (M<10 Mʘ) feedback yields a self-regulated star-formation
preferentially in massive
-Frequent encounters continuously destabilize an appreciable fraction of such a gas triggering:
haloes with larger cross
- fast BH accretion: QSO at full Eddington rate
section for interactions.
- Powerful starbursts (up to 103 Mʘ / yr)
- Building-up of the stellar mass conent
1/3 of the stellar mass in galaxies with M >1010 M is in place at by z≈2
*
ʘ
What about z≈3 ?
At z < 2.
i) Construction of galaxies and merging rate decline
ii) Accretion of smaller lumps by major progenitors
iii) decline of fraction f ≈ j / j of gas accreted by BH or converted in SBursts
Arising of bimodality in the
iv) exaustion of cold gas in massive galaxies
properties of galaxy pop.
(originated from the merging of clumps collapsed in biased,
high-density regions where most of the gas has already been
converted into stars)
v) Lower-mass haloes (MDM > 5 1011 Mʘ) still star forming
• Massive galaxies (MDM > 1013 Mʘ)
vi) Starbursts activity drops especially in massive systems
undergo an almost passive evolution redder
- QSO only occasionally refueled by encounters
colors.
- Emission drops down to L~ 10-2 LEddington
• Residual star formation in less massive
- QSO Lum. Funct. steepens at bright end
galaxies (rates 0.1 – 1 Mʘ/yr) still retaining
part of theircold gas reservoir (blue colors)
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Part of the available cold gas is detabilized and funnelled toward the centre
Cavaliere
Vittorini
2000
1 j 1 m' rd vd
f ( v, V ) 

2 j
2 mbV
(Sanders & Mirabel 96)
3/4 feeds
circumnuclear starbursts
QSO Properties
m acc (v, t ) 
1 f mcold
4
r
c 2 macc
L ( v, t ) 

t
mBH  (1   )  m acc (v, t ' ) dt '
0
Starbursts Properties
3 f mcold
m * (v, t ) 
4
r
t
 * (t  t ' )   (t ' ) dt '
S   m
0
Pre-collision  t ~ 0.01(rinit/h)3/2 trot
As the galaxies fall in towards each other for the first time, they move on simple
parabolic orbits until they are close enough that they have entered each others' dark
halos, and the gravitational force becomes non-Keplerian. During this infall, the galaxies
hardly respond to one another at all, save for their orbital motion.
Impact  t ~ 0.3 (rp/h)3/2 trot As the galaxies reach perigalacticon, they feel the strong
tidal force from one another. The galaxies become strongly distorted, and the tidal tails
are launched from their back sides. Strong shocks are driven in the galaxies' ISM due to
tidal caustics in the disks as well as direct hydrodynamic compression of the colliding
ISM.
Gravitational Response  t ~trot
As the galaxies separate from their initial collision, the disk self-gravity can
amplify the tidal distortions into a strong $m=2$ spiral or bar pattern. This
self-gravitation response is strongly coupled to the internal structure of the
galaxies as well as their orbital motion, resulting in a variety of dynamical
responses
z=3
z=1
z=0.4
Menci et al. 04
MBH~s4
Cold gas mass ~ s2.5
Interactions favour large galact. masses
s3.5
SN feedback disfavours small galact. masses
s4
Data from Gebhardt et al. 2000 (circles)
Ferrarese & Merrit 2000 (squares)
-21< Mr < -19
Local Blue Galaxy Pop.
u-r < 1.3
Local Red Galaxy Pop.
u-r >1.8
log MBH (Mʘ )
The normalization of the QSO LFs
- increases from z=0 to z=2
- decreases for z>2
z=2
z=1.2
z=0.5
The shape of the QSO LFs
progressively flattens for z>2.5
The rise with z of the normalization
is due to the increasing fraction of
destabilized cold gas feeding the BH
BECAUSE
z=3
z=4.2
The encounter rate and the hence
the accretion rate increases with z
The flattening is due to the rapid
exaustion of galactic cold gas in
larger galaxies, whose star formation
is peaked at higher z
Data from Hartwick & Shade 1990, Boyle et al 2000,
Fan et al 2001
The rapid decrease at z<2.5 is
due to 3 concurring factors
1) The decrease with time of the
merging rate of galaxies
2) The decrease with time of the
galactic cold gas left available for
accretion
3) The decrease with time of the
encounter rate stimulating the
cold gas funneling toward the
nucleus
Previous works adopting SAMs
treated the accreted fraction f
as a free parameter constant with z
(missed process #3)
Data from Hartwick & Shade 1990, Warren, Hewitt, Osmer 1994,
Goldschmidt & Miller 1998, Boyle et al 2000, Fan et al 2001
The effect of Starbursts on the Galaxy Lum. Function.
Cold Gas destabilization from
Fly-by interactions strongly
decreases from z=3 to z=0
At high z a large amount of
cold gas is destabilized
Strong starbursts are
expected at z > 3-4
NM et al. 2004
Data from Steidel et al. 99
The effect of Starbursts
induced by fly-by events in
the K-band observables
NM et al 2004
K-band z-counts
K-band Lumin. Functions
The stellar Mass Function (Fontana et al. 04)
Data from Fontana et al. 03
The Global Picture
At z > 2.5 - 3
rapid merging, frequent encounters allow continuous
refueling of gas in the growing galactic haloes.
Frequent encounters continuously destabilize
appreciable fraction of such a gas triggering:
an
fast BH accretion: QSO at full Eddington rate
- powerful starbursts
Such processes are produced preferentially in massive
haloes due to their larger cross section for
interactions.
At z < 2.5 - 3
i) Construction of galaxies and merging rate decline
ii) decline of accreted fraction f ≈ j / j
iii) exaustion of cold gas particulary in massive
galaxies (originated from the merging of clumps
collapsed in biased, high-density regions where
most of the gas has already been converted into
stars)
- QSO only occasionally refueled by encounters
- Emission drops down to L~ 10-2 LEddington
- QSO Lum. Funct. steepens at bright end



Starbursts activity drops
Massive galaxies (MDM > 1013 M⊙) undergo an
almost passive evolution
redder colors
Residual star formation in less massive galaxies
which still retain part of their cold gas
Evolutinary Tracks
Galaxies with DM mass of:
M=1013 M⊙
M=1012 M⊙
M=2.5 1011 M⊙
M=5 1010 M⊙