Omega_matter = 1 (was Re: gas question)

[Boud Roukema]

Witam,
   "Burbidge/Hoyle/Narlikar Reloaded"

According to Vauclair, Blanchard et al., the physics of gas in galaxy
clusters is either:
- in error by a factor of (1+z) in the standard M-T relation (Mass-Temperature)
- correct and  0.85 \ltapprox Omega_matter \ltapprox 1.0

Factors of (1+z) are easy to get wrong if you do things a little too
quickly and your intuition and the formulae don't quite match... Could it
be that this is simply an (1+z) error that got propagated in the cluster
community and noone so far has spotted where the error is? This would make
a nice quick, short paper if anyone can find the error (and be sure of it)...

pozd
boud




http://arxiv.org/abs/astro-ph/0311381

On Mon, 10 Nov 2003, Gary Mamon wrote:

> Hello Andrzej!
>
> >> 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.
>
> > Gary, and how about the more "natural" explanation of that pollution with
> > heavy elements. What I mean is that the intracluster gas (partly) comes
> > from... the galaxy collisions. Such collisions are inelastic w.r.t. the gas
> > and so the scenario seems to be the following:
> >
> > 1. The stars "pass through" although, of course, the structure/shape of the
> >    galaxies is - as we perfectly know - significantly disturbed.
> > 2. The galactic gas stays "in place"
> > 3. The galactic gas heats up.
> >
> > The net result is the following:
> >
> > 1. Galaxies emerging from collisions are deprived of some gas and since the
> > gas mainly sits in galactic disks they are deprived of disks i.e. the become
> > more and more elliptical. And *this* is what we actually observe!
> >
> > 2. Intracluster gas gets enriched by the galactic gas which in turn - as we
> > perfectly know again - is reprocessed ("polluted") in the ("original")
> > galaxies mainly by SNe.
> >
> > 3. The gas is hot because the kinetic energy of colliding galaxies is
> > converted into the heat.
>
> Well, the standard picture that I had in mind is very close to yours (Spitzer
> & Baade 1951 revisited?), except that the collisions do not involve the
> galaxies as we see them, but the galaxies with their dark matter halos, as
> well as gas reservoirs originally attached to these halos. The other
> difference is that when two of these halos merge (and they do so more often
> than the visible parts of galaxies, because the halo cross-section is
> naturally much larger than that of the visible galaxies), the hot gas (and
> dark matter) becomes common to both galaxies. With subsequent halo merging,
> you build a group ... then a cluster.
>
> The gas reservoirs are shock heated during halo collisions, and the
> temperatures found with X-ray spectra are consistent with the velocity
> dispersions of the groups and clusters (i.e. the ratio called beta_spec
> between orbital kinetic and thermal energies is close to unity).
>
> This idea rests upon the assumption (that I have not verified) that most of
> the gas connected to spiral galaxies lies outside of the visible (optical)
> disk, and perhaps outside of the HI disk (since the gas reservoir is expected
> to have a spheroidal shape similar to that of the dark matter). The mass of
> gas in this spheroidal reservoir should be equal to the universal baryonic
> fraction (set by, e.g., WMAP) times the mass within the virial radius minus
> the mass in stars and in disk gas, and one should compare this to the mass in
> disk gas.
>
> Another cute idea (Larson, Tinsley & Caldwell 1980; Whitmore, Gilmore &
> Jones 92?) is that, in clusters, the gas reservoirs are tidally stripped
> before they can begin to cool and settle into a cold disk to form stars,
> and Whitmore et al. have shown that the amount of X-ray gas corresponds to
> the mass of these tidally stripped reservoirs. My criticism of that idea
> is that clusters are built from the mergers of smaller groups of galaxies,
> themselves built from the mergers of single galaxies, for which the tidal
> effects should be small, while the shock heating of the colliding gas
> reservoirs is inevitable.
>
> 	best regards
>
> 	Gary
>