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Issue A&A
Volume 370, Number 1, April IV 2001
Page(s) L26 - L30
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20010333



A&A 370, L26-L30 (2001)
DOI: 10.1051/0004-6361:20010333

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

C. Brüns1, 2, J. Kerp1 and A. Pagels1

1  Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
2  The Australia Telescope National Facility, CSIRO, PO Box 76, Epping NSW 1710, Australia

(Received 14 December 2000 / Accepted 7 March 2001 )

Abstract
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 $FWHM \approx 5$ km s-1 (Westerbork data show $FWHM \approx 2$ km s-1, Braun & Burton 2000) and one with $FWHM \approx 18$ 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 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) 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 $n_{\rm IGM}< 7.8 10^{-6}$ cm-3 and $T_{\rm IGM}> 1.1 10^{5}$ K of the intergalactic medium of the Local Group.


Key words: ISM: clouds, kinematics and dynamics -- Galaxy: halo -- galaxies: intergalactic medium

Offprint request: C. Brüns, cbruens@astro.uni-bonn.de

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© ESO 2001


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