Context. We present deep H observations of three compact high-velocity clouds (CHVCs).Aims. The main goal is to study their diffuse warm gas and compact cold cores. We use both low-and high-resolution data obtained with the 100 m Effelsberg telescope and the Westerbork Synthesis Radio Telescope (WSRT). The combination is essential in order to study the morphological properties of the clouds since the single-dish telescope lacks a sufficient angular resolution while the interferometer misses a large portion of the diffuse gas. Methods. Here single-dish and interferometer data are combined in the image domain with a new combination pipeline. The combination makes it possible to examine interactions between the clouds and their surrounding environment in great detail. Results. The apparent difference between single-dish and radio interferometer total flux densities shows that the CHVCs contain a considerable amount of diffuse gas with low brightness temperatures. A Gaussian decomposition indicates that the clouds consist predominantly of warm gas.
The short-spacing problem describes the inherent inability of radio-interferometric arrays to measure the integrated flux and structure of diffuse emission associated with extended sources. New interferometric arrays, such as Square Kilometer Array (SKA), require solutions to efficiently combine interferometer and single-dish data. We present a new and open-source approach for merging single-dish and cleaned interferometric datasets, requiring a minimum of data manipulation while offering a rigid flux determination and full high-angular resolution. Our approach combines single-dish and cleaned interferometric data in the image domain. This approach is tested for both galactic and extragalactic HI datasets. Furthermore, a quantitative comparison of our results with commonly used methods is provided. Additionally, for the interferometric datasets of NGC 4214 and NGC 5055, we study the impact of different imaging parameters as well as their influence on the combination for NGC 4214. The approach does not require raw data (visibilities) or any additional special information, such as antenna patterns. This is advantageous, especially in the light of upcoming radio surveys with heterogeneous antenna designs.
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