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Context: H\alpha images of star bursting irregular galaxies reveal a largeamount of extended ionized gas structures, in some cases at kpc-distance awayfrom any place of current star forming activity. A kinematic analysis ofespecially the faint structures in the halo of dwarf galaxies allows insightsinto the properties and the origin of this gas component. This is important forthe chemical evolution of galaxies, the enrichment of the intergalactic medium,and for the understanding of the formation of galaxies in the early universe.  Aims: We want to investigate whether the ionized gas detected in twoirregular dwarf galaxies (NGC 2366 and NGC 4861) stays gravitationally bound tothe host galaxy or can escape from it by becoming a freely flowing wind.  Methods: Very deep H\alpha images of NGC 2366 and NGC 4861 were obtained todetect and catalog both small and large scale ionized gas structures down tovery low surface brightnesses. Subsequently, high-resolution long-slit echellespectroscopy of the H\alpha line was performed for a detailed kinematicanalysis of the most prominent filaments and shells. To calculate the escapevelocity of both galaxies and to compare it with the derived expansionvelocities of the detected filaments and shells, we used dark matter halomodels.  Results: We detected a huge amount of both small scale (up to a few hundredpc) and large scale (about 1-2 kpc of diameter or length) ionized gasstructures on our H\alpha images. Many of the fainter ones are new detections.The echelle spectra reveal outflows and expanding bubbles/shells withvelocities between 20 and 110 km/s. Several of these structures are inaccordance with filaments in the H\alpha images. A comparison with the escapevelocities of the galaxies derived from the NFW dark matter halo model showsthat all gas features stay gravitationally bound.

Outflow or galactic wind: The fate of ionized gas in the halos of dwarf galaxies