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Astron. Astrophys. 332, L61-L64 (1998)

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5. Results and discussion

The accuracy of the LDS has been improved by eliminating intensities received as reflections from ground. The emission at [FORMULA] 250 positions after averaging over [FORMULA] was decomposed into Gaussian components. We find evidence for large-scale galactic HI emission with a velocity dispersion of 60 [FORMULA] [FORMULA] and a column density of [FORMULA] cm-2 projected to the north galactic pole. Assuming that this gas is co-rotating with the disk, the observed extended wings in the profiles can be modeled. The [FORMULA] distribution is characterized by a hydrostatic equilibrium with a mid-plane density [FORMULA] cm-3 in the solar vicinity. The exponential scale height is [FORMULA] kpc, the radial scale length is [FORMULA] kpc.

Our analysis implies that H gas due to its turbulent pressure remains an important constituent of the halo at z [FORMULA] 1 kpc. In particular the scale height of the Reynolds layer (880 pc, Taylor & Cordes 1993) is exceeded considerably. On the other hand, halo gas at temperatures of [FORMULA] K is needed to explain the soft X-ray background (Kerp 1994). Pietz et al. (1998) modeled the X-ray background in the 1/4 and 3/4 keV range and concluded that the X-ray halo is defined by the same model parameters as given in Sect. 4. This implies, that the galactic halo has a multi-phase composition with temperatures ranging from [FORMULA] to [FORMULA] K. Transition regions between these phases may exist, as indicated by highly ionized gas at intermediate temperatures. It appears plausible to assume that the highly ionized gas components in the halo share the turbulent properties of the H gas. This conclusion is supported by Savage et al. (1997) who found turbulent velocities of [FORMULA] [FORMULA] for the [FORMULA] lines. They derive a scale height of [FORMULA] kpc which is in excellent agreement with the H scale height derived here. We conclude that the highly ionized gas components must be intermixed with H gas as analyzed in this letter.

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© European Southern Observatory (ESO) 1998

Online publication: March 30, 1998