H I observations of three compact high-velocity clouds around the Milky Way

Abstract

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.

A High-Velocity Cloud Impact Forming a Supershell in the Milky Way

“…The velocity width of the mean profile is 45 km s −1 , which is considerably larger than the median value (36 km s −1 ) of individual profiles, presumably due to the dispersion of central velocities. The median width corresponds to a kinetic temperature of 2.8 × 10 4 K. At several positions, narrow velocity components are detected, but still their widths are ≥ 10 km s −1 , which implies a kinetic temperature ≥ 2,000 K. This indicates that CHVC040 is mostly composed of warm neutral gas, which is not unusual for CHVCs (Winkel et al 2011;Faridani et al 2014). But it is different from those head-tail HVCs with a narrow-line head of undisturbed cold Hi gas and a wide-line tail of disturbed warm Hi gas (e.g., HVC125+41-207; Brüns et al 2001).…”

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High-resolution HI and CO observations of high-latitude intermediate-velocity clouds

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