gas question

[Gary Mamon]

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