We present three‐dimensional hydrodynamic simulations of ram pressure stripping in dwarf galaxies. Analogous studies on this subject usually deal with much higher ram pressures, typical of galaxy clusters, or mild ram pressure due to the gas halo of the massive galactic companions. We extend over previous investigations by considering flattened, rotating dwarf galaxies subject to ram pressures typical of poor galaxy groups. We study the ram pressure effects as a function of several parameters such as galactic mass and velocity, ambient gas density and the angle between the galactic plane and the direction of motion. It turns out that this last parameter plays a role only when the gas pressure in the galactic centre is comparable to the ram pressure. Despite the low values of the ram pressure, some dwarf galaxies can be completely stripped after 1–2 Myr. This poses an interesting question on the aspect of the descents and, more in general, on the morphological evolution of dwarf galaxies. In cases in which the gas is not completely stripped, the propagation of possible galactic wind may be influenced by the disturbed distribution of the interstellar matter. We also consider the modification of the interstellar matter surface density induced by the ram pressure and find that the resulting compression may trigger star formation over long time‐spans.

We present 3D hydrodynamic simulations aimed at studying the dynamical and chemical evolution of the interstellar medium in dwarf spheroidal galaxies. This evolution is driven by the explosions of Type II supernovae (SNe II) and Type Ia supernovae (SNe Ia), whose different contribution is explicitly taken into account in our models. We compare our results with detailed observations of the Draco galaxy. We assume star formation histories consisting of a number of instantaneous bursts separated by quiescent periods. Diverse histories differ by the number of bursts, but all have the same total duration and give rise to the same amount of stars. Because of the large effectiveness of the radiative losses and the extended dark matter halo, no galactic wind develops, despite the total energy released by the supernovae is much larger than the binding energy of the gas. This explains why the galaxy is able to form stars for a long period (>3 Gyr), consistently with observations. In this picture, the end of the star formation and gas removal must result from external mechanisms, such as ram pressure and/or tidal interaction with the Galaxy. The stellar [Fe/H] distributions found in our models match very well the observed ones. We find a mean value 〈[Fe/H]〉=−1.65 with a spread of ∼1.5 dex. The chemical properties of the stars derive by the different temporal evolution between SNe Ia and SNe II rate, and by the different mixing of the metals produced by the two types of supernovae. We reproduce successfully the observed [O/Fe]–[Fe/H] diagram. However, our interpretation of this diagram differs from that generally adopted by previous chemical models. In fact, we find that the break observed in the diagram is not connected with the onset of a galactic wind or with a characteristic time‐scale for the sudden switchover of the SNe Ia, as sometimes claimed. Instead, we find that the chemical properties of the stars derive, besides the different temporal evolution of the SNe II and SNe Ia rates, from the spatial inhomogeneous chemical enrichment due to the different dynamical behaviour between the remnants of the two types of supernovae.

Superwinds from starburst galaxies are multiphase outflows that sweep up and incorporate ambient galactic disc and halo gas. The interaction of this denser material with the more diffuse hot wind gas is thought to give rise to the O VI emission and absorption in the far ultraviolet (FUV) and the soft thermal X-ray emission observed in superwinds. In this paper, we present high-resolution hydrodynamical models of warm ionized clouds embedded in a superwind, and compare the O VI and soft X-ray properties to the existing observational data. These models include thermal conduction, which we show plays an important role in shaping both the dynamics and radiative properties of the resulting wind/cloud interaction. Heat conduction stabilizes the cloud by inhibiting the growth of Kelvin-Helmholtz and Rayleigh-Taylor instabilities, and also generates a shock wave at the cloud's surface that compresses the cloud. This dynamical behaviour influences the observable properties. We find that while O VI emission and absorption always arises in cloud material at the periphery of the cloud, most of the soft X-ray arises in the region between the wind bow shock and the cloud surface, and probes either wind or cloud material depending on the strength of conduction and the relative abundances of the wind with respect to the cloud. In general, only a small fraction ( 1 per cent) of the wind mechanical energy intersecting a cloud is radiated away at ultraviolet (UV) and X-ray wavelengths, with more wind energy going into accelerating the cloud. Clouds in relatively slow cool winds radiate a larger fraction of their energy, which are inconsistent with observational constraints. Models with heat conduction at Spitzer-levels are found to produce observational properties closer to those observed in superwinds than models with no thermal conduction, in particular, in terms of the O VI to X-ray luminosity ratio, but cloud life times are uncomfortably short ( 1 Myr) compared to the dynamical ages of real winds. We experimented with reducing the thermal conductivity for one set of model parameters, and found that even when we reduced conduction by a factor of 25 that the simulations retained the beneficial hydrodynamical stability and low O VI to X-ray luminosity ratio found in the Spitzer-level conductive models, while also having reduced evaporation rates. Although more work is required to simulate clouds for longer times and to investigate cloud acceleration and thermal conduction at sub-Spitzer levels in a wider range of models, we conclude that thermal conduction can no longer be ignored in superwinds.