Stellar Feedback Effects on Galaxy Formation Filippo Sigward Università di Firenze Dipartimento 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 ? 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” 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 preheating Benson & Madau 2003 Increased gas pressure by winds from pregalactic starburst & energy deposited by accreting BH. Global early energy input: “preheating” LF Observed Good 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 Studies Mechanical evaporation Mechanical evaporation : T s > T vir – Cooling : Baryonic stripping Baryonic stripping: f M s v s  M b v e (Scannapieco, Ferrara & Broadhurst 2000) CDM  CDM

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

Initial conditions - Shock: 1 SN occurs every 100 M  of baryons that form stars  sf = 0.1 E tot / SN = 2  erg Outflows initialization: thin shell approximation R s = mean distance between the halos  plane wave (R s  R vir,ta ) - IGM:  igm homogeneous, T = 10 4 K

Pre-virialized case distance [kpc]  b [g cm –3 ] distance [kpc] v [cm s –1 ]  b  r –2.25 Similarity solutions for infall and accretion onto an overdense perturbation (Bertschinger 1985). R ta  t 8/9 M(r < R ta )  t 2/3 Particles come to rest after the shock

Pre-virialized case Simulation parameters: Initial density [g cm –3 ]  x  138 pc 20.7 kpc

Final maps Pre-virialized case Density [g cm –3 ]Temperature [K] t = 133 Myr R ta

- Dark Matter profile (NFW): - Baryonic profile: Virialized case characteristic overdensity  b [g cm –3 ] distance [kpc]

Simulation parameters: Initial density [g cm –3 ] Virialized case  x  43 pc 6.5 kpc

Density maps: evolution Virialized case 6.5 kpc time: Myr

Temperature evolution [K] V Temperature evolution [K] Virialized case t = 17.5 Myr t = 52.4 Myr

Final maps Virialized case t = 58.2 Myr Density [g cm –3 ]Temperature [K] R vir

Amount of Gas Removed M b (T > T vir ) / M b ~ 5.0% M b ( v  v e ) / M b ~ 69.9% t f = 133 Myr Pre-virialized case total v  v e T > T vir t [Myr] M b out (t) / M b (t)

t [Myr] T > T vir v  v e M b (T > T vir ) / M b ~ 0.9% M b ( v  v e ) / M b ~ 0.7% t f = 58.2 Myr Virialized case total Amount of Gas Removed Amount of Gas Removed

Conclusions 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.