stellar feedback effects on galaxy formation filippo sigward università di firenze dipartimento di...
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Stellar Feedback EffectsStellar Feedback Effectson Galaxy Formationon Galaxy Formation
Filippo Sigward
Università di FirenzeDipartimento di Astronomia e Scienza dello Spazio
Japan – Italy Joint Seminar“Formation of the First Generation of Galaxies: Strategy for
the Observational Corroboration of Physical Scenarios”
December 2 – 5, 2003 – Niigata University, Japan
Andrea Ferrara, SISSA / ISAS
Evan Scannapieco, KITP, SB
Why Feedback ?Why Feedback ?
Ingredients for Galaxy formation and evolution:
• Evolution of dark halos• Cooling and star formation • Chemical enrichment• Stellar populations
Model outputs
Comparison with observations
• Feedback
The “cooling catastrophe”The “cooling catastrophe”
In the absence of any contrasting effect, much of the gas is expected to sink into small halos at early epochs
Strong feedback is invocated to avoid too many baryons turning into stars at primeval ages
Early preheatingEarly preheating
Benson & Madau 2003
Increased gas pressure by winds from pregalactic starburst & energy deposited by accreting BH.
Global early energy input: “preheating”
LF
ObservedGood agreement
in the faint-end slope
Unable to explain the cut-off at bright magnitudes
Additional feedback processes to suppress dwarf galaxies: SN-driven shocks from nearby galaxies
Previous Analytical StudiesPrevious Analytical Studies
Ctn
kTcool
e
s 2
3
• Mechanical evaporationMechanical evaporation:
Ts > Tvir
– Cooling:
• Baryonic strippingBaryonic stripping:
f Ms vs Mb ve
(Scannapieco, Ferrara & Broadhurst 2000)
CDM
CDM
Numerical simulationsNumerical simulations
• Pre-virialized case: Bertschinger 1985 (analytical and semi-analytical
solutions)
• Virialized case: Navarro, Frenk & White 1997 (cosmological simulations)
Initial conditionsInitial conditions
- Shock:
1 SN occurs every 100 M of baryons that form stars
sf = 0.1
Etot / SN = 2 1051 erg
Outflows initialization: thin shell approximation
Rs = mean distance between the halos
plane wave (Rs Rvir,ta)
- IGM: igm homogeneous, T = 104 K
Pre-virialized casePre-virialized case
distance [kpc]
b[
g cm
–3]
distance [kpc]
v [c
m s
–1]b r –2.25
Similarity solutions for infall and accretion onto an overdense perturbation (Bertschinger 1985).
Rta t8/9 M(r < Rta) t2/3
Particles come to rest after the shock
37
9
10 18
M
z
hMM
Pre-virialized case
kpc735.taR
Simulation parameters:Initial density [g cm–3]
x 138 pc
20.7 kpc
Final mapsFinal mapsPre-virialized case
Density [g cm–3] Temperature [K]
t = 133 Myr
Rta Rta
22000
02
exp0 22
cb
eevir
pbb r
kT
mr
vv
- Dark Matter profile (NFW):
- Baryonic profile:
Virialized caseVirialized case
c
vir
cc
c
R
rx
cxcxr
84
1 2
.
characteristic overdensity
b [
g cm
–3]
distance [kpc]
14
9
10 18
M
z
hMM
kpc751.virR
K12490virT
138 skmvire Rv
Simulation parameters:Initial density [g cm–3]
Virialized case
x 43 pc
6.5 kpc
Density maps: evolutionDensity maps: evolutionVirialized
case
6.5 kpc
time: 0 - 58.2 Myr
Final mapsFinal mapsVirialized case
t = 58.2 Myr
Density [g cm–3] Temperature [K]
RvirRvir
Amount of Gas RemovedAmount of Gas Removed
Mb (T > Tvir) / Mb ~ 5.0%
Mb (v ve ) / Mb ~ 69.9%
tf = 133 Myr
Pre-virialized case total
v ve
T > Tvir
t [Myr]
Mbou
t (t)
/ Mb(
t)
Mbou
t (t)
/ Mb(
t)
t [Myr]
T > Tvir
v ve
Mb (T > Tvir) / Mb ~ 0.9%
Mb (v ve ) / Mb ~ 0.7%
tf = 58.2 Myr
Virialized case total
Amount of Gas RemovedAmount of Gas Removed
ConclusionsConclusions
2. Such feedback is much less efficient (a few % mass loss) if the system is already virialized.
3. Gas is predominantly removed via baryonic stripping; mechanical evaporation is not efficient due to rapid cooling of the halo gas.
1. Strong suppression of dwarf galaxy formation by shocks from nearby galaxies can occur in the collapse stage immediately after the turn-around.