We present results from a fully cosmological, very high-resolution, LCDM
"zoom-in" simulation of a group of seven field dwarf galaxies with present-day
virial masses in the range M_vir=4.4e8-3.6e10 Msun. The simulation includes a
blastwave scheme for supernova feedback, a star formation recipe based on a
high gas density threshold, metal-dependent radiative cooling, a scheme for the
turbulent diffusion of metals and thermal energy, and a uniform UV background
that modifies the ionization and excitation state of the gas. The properties of
the simulated dwarfs are strongly modulated by the depth of the gravitational
potential well. All three halos with M_vir < 1e9 Msun are devoid of stars, as
they never reach the density threshold for star formation of 100 atoms/cc. The
other four, M_vir > 1e9 Msun dwarfs have blue colors, low star formation
efficiencies, high cold gas to stellar mass ratios, and low stellar
metallicities. Their bursty star formation histories are characterized by peak
specific star formation rates in excess of 50-100 1/Gyr, far outside the realm
of normal, more massive galaxies, and in agreement with observations of extreme
emission-line starbursting dwarfs by the Cosmic Assembly Near-IR Deep
Extragalactic Legacy Survey. Metal-enriched galactic outflows produce sub-solar
effective yields and pollute with heavy elements a Mpc-size region of the
intergalactic medium, but are not sufficient to completely quench star
formation activity and are not ubiquitous in our dwarfs. Within the limited
size of the sample, our simulations appear to simultaneously reproduce the
observed stellar mass and cold gas content, resolved star formation histories,
stellar kinematics, and metallicities of field dwarfs in the Local Volume.Comment: 15 pages, 10 figures, version accepted for publication in The
Astrophysical Journa
