The effect of metal enrichment and galactic winds on galaxy formation in
  cosmological zoom simulations
  We investigate the differential effects of metal cooling and galactic stellar
winds on the cosmological formation of individual galaxies with three sets of
cosmological, hydrodynamical zoom simulations of 45 halos in the mass range
10^11<M_halo<10^13M_sun. Models including both galactic winds and metal cooling
(i) suppress early star formation at z>1 and predict reasonable star formation
histories, (ii) produce galaxies with high cold gas fractions (30-60 per cent)
at high redshift, (iii) significantly reduce the galaxy formation efficiencies
for halos (M_halo<10^12M_sun) at all redshifts in agreement with observational
and abundance matching constraints, (iv) result in high-redshift galaxies with
reduced circular velocities matching the observed Tully-Fisher relation at z~2,
and (v) significantly increase the sizes of low-mass galaxies
(M_stellar<3x10^10M_sun) at high redshift resulting in a weak size evolution -
a trend in agreement with observations. However, the low redshift (z<0.5) star
formation rates of massive galaxies are higher than observed (up to ten times).
No tested model predicts the observed size evolution for low-mass and high-mass
galaxies simultaneously. Due to the delayed onset of star formation in the wind
models, the metal enrichment of gas and stars is delayed and agrees well with
observational constraints. Metal cooling and stellar winds are both found to
increase the ratio of in situ formed to accreted stars - the relative
importance of dissipative vs. dissipationless assembly. For halo masses below
~10^12M_sun, this is mainly caused by less stellar accretion and compares well
to predictions from semi-analytical models but still differs from abundance
matching models. For higher masses, the fraction of in situ stars is
over-predicted due to the unrealistically high star formation rates at low
redshifts.
