Low-mass galaxy formation in cosmological AMR simulations: the effects
  of varying the sub-grid physics parameters
  We present numerical simulations aimed at exploring the effects of varying
the sub-grid physics parameters on the evolution and the properties of the
galaxy formed in a low-mass dark matter halo (~7 times 10^10 Msun/h at redshift
z=0). The simulations are run within a cosmological setting with a nominal
resolution of 218 pc comoving and are stopped at z = 0.43. In all of our
simulations, an extended old/intermediate-age stellar halo and a more compact
younger stellar disk are formed. We found that a non negligible fraction of the
halo stars are formed in situ in a spheroidal distribution. Changes in the
sub-grid physics parameters affect significantly and in a complex way the
evolution and properties of the galaxy: (i) Lower threshold densities nsf
produce larger stellar effective radii Re, less peaked circular velocity curves
V_c(R), and greater amounts of low-density and hot gas in the disk mid-plane;
(ii) When stellar feedback is modeled by temporarily switching off radiative
cooling in the star forming regions, Re increases (by a factor of ~ 2 in our
particular model), the circular velocity curve becomes flatter, and a complex
multi-phase gaseous disk structure develops; (iii) A more efficient local
conversion of gas mass to stars, measured by a stellar particle mass
distribution biased toward larger values, increases the strength of the
feedback energy injection -driving outflows and inducing burstier SF histories;
iv) If feedback is too strong, gas loss by galactic outflows -which are easier
to produce in low-mass galaxies- interrupts SF, whose history becomes episodic.
The simulations exhibit two important shortcomings: the baryon fractions are
higher, and the specific SF rates are much smaller, than observationally
inferred values for redshifts ~ 0.4-1.
