Hi Bartek,
Is it correct that intergalactinc gas, made of relativistic electrons, seen in X-rays by bremstrahlung rediation caused by collisions with DM particles, comes originally from galaxies, where the electrons are accelerated in galactic magnetic fields and SN explosions and then some of them escape the galactic grawitation ?
The X-ray emission of hot (10^8 K) intracluster gas indeed arises mainly from bremsstrahlung radiation, caused by collisions between charged particles, independent of the existence or not of dark matter. For small groups, half of the emission comes from a multitude of spectral lines.
The origin of the gas is not completely clear. The standard idea is that the bulk of the gas (in fraction of mass) is primordial and collapsed with the dark matter when the system components (the groups that later merged into present-day clusters) collapsed.
However, the abundance of heavy elements is roughly 1/3 solar in clusters, instead of near-zero predicted if the gas wewre primordial. So, in the standard picture, the gas is polluted by galaxy winds caused by supernovae, and the bulk of the metals (heavy elements) comes from the galaxies, even though the galactic winds contribute little to the mass of the hot intracluster gas.
As for the idea of electrons escaping the magnetic field of the galaxy, I don't know. The supernovae idea involves bulk flows of insterstellar gas being shock heated by the supernova explosions (which tend to occur in small regions of galactic space during short time intervals, and thus collectively blow out a wind, which escapes perpendicular to the plane of a spiral galaxy). This hot interstellar gas is mainly consitituted of protons, electrons plus the heavy elements from the supernova remnant. I believe that the electrons are coupled to the protons and other positively charged ions, so that ambipolar diffusion would be too small to explain the hot intracluster gas. Furthermore, with ambipolar diffusion, you would not get positively charged ions of heavy elements, contrary to what is inferred from X-ray spectra. I am not sure that the global galactic magnetic fields are strong enough to prevent the supernova winds from being ejected.
cheers
Gary