Deep H I observations of the compact high-velocity cloud HVC 125+41-207

We present deep HI observations of the compact high-velocity cloud HVC 125+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 reveals a two phase core/halo structure - one component with a velocity width of FWHM approximately equals 5 km s-1 (Westerbork data show FWHM approximately equals 2 km s-1, Braun and Burton 2000) and one with FWHM approximately equals 18 km s-1. 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 H I 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 H I data of this HVC (Braun and Burton 2000) reveals 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 HVC 125+41-207. Following these considerations, it is possible to constrain the parameters nIGM less than or equal 7.8 10-6 cm-3 and TIGM > 1.1 105 K of the intergalactic medium of the Local Group.