The distribution of mass in dwarf galaxies and the structure of their ISM

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Central to this project is the efficient use of the Very Large Array (VLA) to carry out HI measurements of the disks of a carefully selected sample of low-mass (or dwarf) and gas-rich galaxies down to very low column densities and with high spectral resolution. Their stellar disks will be investigated with deep near-infrared (NIR) photometry, mainly using the INT at La Palma. The science goals, which naturally arise from our (and others ) previous studies, are as follows:- The overall gravitational potential will be explored by deriving high-quality rotation curves. This facilitates a mass decomposition into the (stellar and gaseous) baryonic and Dark Matter (DM). - The sizes of the gaseous disks, not very well known for dwarf galaxies, will be explored down to the lowest gas column densities achievable. This is the only means to estimate the total size and mass of this kind of galaxies. The sizes of the stellar disks will be determined using NIR photometry. These will be compared to the sizes of the gas disks.- The radio and optical observations will also be conveniently used to carry out mass decompositions, thereby studying the distribution of the baryonic and dark matter constituents.- The structure of the interstellar medium (ISM) will be investigated using the HI data cubes. In particular, the statistics of HI holes will be established, and their size distribution be studied with respect to the disk thicknesses and depth of gravitational potentials.- Using the surface mass densities of the stellar and gaseous constituents, the conditions for (past and future) star formation will be assessed via the Toomre criterion. This will shed light on the lack of star formation in the outer gaseous disks.These measurements and analyses will be efficiently combined such as to achieve an overall understanding of the nature of gas-rich dwarf galaxies. The derived mass distributions and gravitational potentials deliver boundary conditions for the structure of the gaseous disks, i.e. their thickness and size distribution of bubbles. Achieving this goal is facilitated by our newly developed software tools, which allows to derive the three-dimensional structure of the gaseous disks. Furthermore, the relation between the size of the stellar and gaseous disk will be extended to the low-mass end of galaxies. It is the for the first time that such a systematic study will be conducted.