The composition of the interstellar medium towards the Lockman Hole. H I, UV and X-ray observations
M. Kappes, J. Kerp, P. Richter;
AaA, 2003, 405, 607
ABSTRACT: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 \ion{H}{i} 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 \ion{H}{i} 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.
KEYWORDS: x-rays: diffuse background, x-rays: ism, ultraviolet: ism, galaxy: halo, galaxy: structure
PERSOKEY:h_i, uv, xrays, ,
CODE: kappes2003