Deep H I observations of the compact high-velocity cloud HVC125+41-207

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Abstract
We present deep HI observations of the compact high-velocity cloud HVC125+41-207 using the 100-m Effelsberg telescope. Our goal was in particular to study the warm neutral medium (WNM) in detail. The Effelsberg data reveal a two phase core/halo structure - one component with a velocity width of FWHM approx 5 km/s (Westerbork data show FWHM approx 2 km/s, Braun & Burton 2000) and one with FWHM approx 18 km/s. The column density distribution of the warmer component is highly asymmetric and shows a head-tail structure. We performed a Gaussian decomposition of the cloud and found that 52% of the HI mass of the cloud is in the WNM. 24% of the WNM is located in the tail. The overall structure and the systematic variation of the observational parameters radial velocity, velocity dispersion and column density indicate that this cloud is currently interacting with the ambient medium. The Westerbork HI data of this HVC (Braun & Burton 2000) reveal an interesting dense condensation. Assuming that this condensation is virialized and in pressure equilibrium with the ambient medium, we derive a distance of 130 kpc for HVC125+41-207. Following these considerations, it is possible to constrain the parameters n_IGM < 7.8 10^-6 cm^-3 and T_IGM > 1.1 10^5 K of the intergalactic medium of the Local Group.

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