Stellar Feedback Effects on Galaxy Formation

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Stellar Feedback Effectson Galaxy Formation
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

• Filippo Sigward
• Università di Firenze
• Dipartimento di Astronomia e Scienza dello Spazio

Andrea Ferrara, SISSA / ISAS Evan Scannapieco,
KITP, SB
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Why Feedback ?
Ingredients for Galaxy formation and evolution

• Evolution of dark halos
• Cooling and star formation
• Chemical enrichment
• Stellar populations

• Feedback

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Comparison with observations

Model outputs
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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
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Early preheating
Increased gas pressure by winds from pregalactic
starburst energy deposited by accreting
BH. Global early energy input preheating
LF
Unable to explain the cut-off at bright magnitudes
Observed
Good agreement in the faint-end slope
? Additional feedback processes to suppress dwarf
galaxies SN-driven shocks
from nearby galaxies
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Previous Analytical Studies

CDM
Mechanical evaporation Ts gt Tvir
Cooling
?CDM
Baryonic stripping f Ms vs ? Mb ve
(Scannapieco, Ferrara Broadhurst 2000)
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Numerical simulations

• Pre-virialized case Bertschinger 1985
• (analytical and semi-analytical solutions)
• Virialized case Navarro, Frenk White 1997
• (cosmological simulations)

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Initial 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

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Pre-virialized case
Similarity solutions for infall and accretion
onto an overdense perturbation (Bertschinger
1985).
Rta ? t8/9 M(r lt Rta) ? t2/3
Particles come to rest after the shock
?b ? r 2.25
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Initial density g cm3
Simulation parameters
Pre-virialized case
?x ? 138 pc
20.7 kpc
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Final maps
Pre-virialized case
t 133 Myr
Rta
Rta
Density g cm3
Temperature K
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Virialized case
- Dark Matter profile (NFW)
- Baryonic profile
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Initial density g cm3
Simulation parameters
Virialized case
?x ? 43 pc
6.5 kpc
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Density maps evolution
Virialized case
6.5 kpc
time 0 - 58.2 Myr
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Temperature evolution K Virialized case
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Final maps
Virialized case
t 58.2 Myr
Rvir
Rvir
Density g cm3
Temperature K
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Amount of Gas Removed
Pre-virialized case
Mb (T gt Tvir) / Mb 5.0
tf 133 Myr
Mb (v ? ve ) / Mb 69.9
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Amount of Gas Removed
Virialized case
total
Mb (T gt Tvir) / Mb 0.9
tf 58.2 Myr
Mb (v ? ve ) / Mb 0.7
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Conclusions

• Strong suppression of dwarf galaxy formation by
  shocks from nearby galaxies can occur in the
  collapse stage immediately after the turn-around.

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.