Volume 405, Number 2, July II 2003
|Page(s)||607 - 616|
|Section||Interstellar and circumstellar matter|
|Published online||19 June 2003|
The composition of the interstellar medium towards the Lockman Hole
, UV and X-ray observations
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany e-mail: firstname.lastname@example.org
2 Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Florence, Italy e-mail: email@example.com
Corresponding author: M. Kappes, firstname.lastname@example.org
Accepted: 18 April 2003
The Lockman Hole is well known as the region with the lowest neutral atomic hydrogen column density on the entire sky. We present an analysis of the soft X-ray background radiation towards the Lockman Hole using ROSAT all-sky survey data. This data is correlated with the Leiden/Dwingeloo survey (Galactic 21 cm-line emission) in order to model the soft X-ray background by using radiative transfer calculations for four ROSAT energy bands simultaneously. It turns out, that an important gas fraction, ranging between 20–50%, of the X-ray absorbing material is not entirely traced by the but is in the form of ionized hydrogen. Far-ultraviolet absorption line measurements by FUSE are consistent with this finding and support an ionized hydrogen component towards the Lockman Hole.
Key words: X-rays: diffuse background / X-rays: ISM / ultraviolet: ISM / Galaxy: halo / Galaxy: structure
© ESO, 2003
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