We present a detailed analysis of the formation, evolution, and possible longevity of metallicity gradients in simulated dwarf galaxies. Specifically, we investigate the role of potentially orbit-changing processes such as radial stellar migration and dynamical heating in shaping or destroying these gradients. We also consider the influence of the star formation scheme, investigating both the low density star formation threshold of 0.1 amu cm −3 , which has been in general use in the field, and the much higher threshold of 100 cm −3 , which, together with an extension of the cooling curves below 10 4 K and and increase of the feedback efficiency, has been argued to represent a much more realistic description of star forming regions.The Nbody-SPH models that we use to self-consistently form and evolve dwarf galaxies in isolation show that, in the absence of significant angular momentum, metallicity gradients are gradually built up during the evolution of the dwarf galaxy, by ever more centrally concentrated star formation adding to the overall gradient. Once formed, they are robust and can easily survive in the absence of external disturbances, with their strength hardly declining over several Gyr, and they agree well with observed metallicity gradients of dwarf galaxies in the Local Group. The underlying orbital displacement of stars is quite limited in our models, being of the order of only fractions of the half light radius over time-spans of 5 to 10 Gyr in all star formation schemes. This is contrary to the strong radial migration found in massive disc galaxies, which is caused by scattering of stars off the corotation resonance of large-scale spiral structures. In the dwarf regime the stellar body only seems to undergo mild dynamical heating, due to the lack of long-lived spiral structures and/or discs.The density threshold, while having profound influences on the star formation mode of the models, has only an minor influence on the evolution of metallicity gradients. Increasing the threshold 1000-fold causes comparatively stronger dynamical heating of the stellar body due to the increased turbulent gas motions and the scattering of stars off dense gas clouds, but the effect remains very limited in absolute terms.

We investigate the evolution of dwarf galaxies using N -body/SPH simulations that incorporate their formation histories through merger trees constructed using the extended Press-Schechter formalism. The simulations are computationally cheap and have high spatial resolution. We compare the properties of galaxies with equal final mass but with different merger histories with each other and with those of observed dwarf spheroidals and irregulars.We show that the merger history influences many observable dwarf galaxy properties. We identify two extreme cases that make this influence stand out most clearly: (i) merger trees with one massive progenitor that grows through relatively few mergers and (ii) merger trees with many small progenitors that merge only quite late. At a fixed halo mass, a type (i) tree tends to produce galaxies with larger stellar masses, larger half-light radii, lower central surface brightness, and since fewer potentially angular momentum cancelling mergers are required to build up the final galaxy, a higher specific angular momentum, compared with a type (ii) tree.We do not perform full-fledged cosmological simulations and therefore cannot hope to reproduce all observed properties of dwarf galaxies. However, we show that the simulated dwarfs are not unsimilar to real ones.

Using computer simulations, we explored gaseous infall as a possible explanation for the starburst phase in Blue Compact Dwarf galaxies. We simulate a cloud impact by merging a spherical gas cloud into an isolated dwarf galaxy. We investigated which conditions were favourable for triggering a burst and found that the orbit and the mass of the gas cloud play an important role. We discuss the metallicity, the kinematical properties, the internal dynamics and the gas, stellar and dark matter distribution of the simulations during a starburst. We find that these are in good agreement with observations and depending on the set-up (e.g. rotation of the host galaxy, radius of the gas cloud), our bursting galaxies can have qualitatively very different properties. Our simulations offer insight in how starbursts start and evolve. Based on this, we propose what postburst dwarf galaxies will look like.

We present infrared luminosity functions and dust mass functions for the EAGLE cosmological simulation, based on synthetic multi-wavelength observations generated with the SKIRT radiative transfer code. In the local Universe, we reproduce the observed infrared luminosity and dust mass functions very well. Some minor discrepancies are encountered, mainly in the high luminosity regime, where the EAGLE-SKIRT luminosity functions mildly but systematically underestimate the observed ones. The agreement between the EAGLE-SKIRT infrared luminosity functions and the observed ones gradually worsens with increasing lookback time. Fitting modified Schechter functions to the EAGLE-SKIRT luminosity and dust mass functions at different redshifts up to z = 1, we find that the evolution is compatible with pure luminosity/mass evolution. The evolution is relatively mild: within this redshift range, we find an evolution of L ,250 ∝ (1 + z) 1.68 , L ,TIR ∝ (1 + z) 2.51 and M ,dust ∝ (1 + z) 0.83 for the characteristic luminosity/mass. For the luminosity/mass density we find ε 250 ∝ (1 + z) 1.62 , ε TIR ∝ (1 + z) 2.35 and ρ dust ∝ (1 + z) 0.80 , respectively. The mild evolution of the dust mass density is in relatively good agreement with observations, but the slow evolution of the infrared luminosity underestimates the observed luminosity evolution significantly. We argue that these differences can be attributed to increasing limitations in the radiative transfer treatment due to increasingly poorer resolution, combined with a slower than observed evolution of the SFR density in the EAGLE simulation and the lack of AGN emission in our EAGLE-SKIRT post-processing recipe.

In this paper, we present a new calculation of composition-dependent radiative cooling and heating curves of low-density gas, intended primarily for use in numerical simulations of galaxy formation and evolution. These curves depend on only five parameters: temperature, density, redshift, [Fe/H], and [Mg/Fe]. They are easily tabulated and can be efficiently interpolated during a simulation.The ionization equilibrium of 14 key elements is determined for temperatures between 10 K and 10 9 K and densities up to 100 amu cm −3 taking into account collisional and radiative ionization, by the cosmic UV background and an interstellar radiation field, and by charge-transfer reactions. These elements, ranging from H to Ni, are the ones most abundantly produced and/or released by SNIa, SNII, and intermediate-mass stars. Self-shielding of the gas at high densities by neutral Hydrogen is taken into account in an approximate way by exponentially suppressing the H-ionizing part of the cosmic UV background for HI densities above a threshold density of n HI,crit = 0.007 cm −3 . We discuss how the ionization equilibrium, and the cooling and heating curves depend on the physical properties of the gas.The main advantage of the work presented here is that, within the confines of a welldefined chemical evolution model and adopting the ionization equilibrium approximation, it provides accurate cooling and heating curves for a wide range of physical and chemical gas properties, including the effects of self-shielding. The latter is key to resolving the formation of cold, neutral, high-density clouds suitable for star formation in galaxy simulations.