Luminous mass fractions in superclusters?

A question about typical galactic superclusters, like Horologium,
Shapley, or
Hydra-Centaurus:

Disregarding their Dark Matter components entirely, and looking only
at the
normal luminous mass content...

What fraction of that luminous mass consists of stars?
What fraction is gas?
What fraction is dust?

thanks,
Gene

I found these figures through Google:

Our Galaxy, like most well-studied spiral galaxies, chiefly consists
of stars, gas, and dust. Studies of its visible disk indicate that
most of the mass is in the stars, with only about 2% gas (mostly
hydrogen) and about 0.01% dust.

and

Composition of a cluster is 10% galaxies, 20% intracluster medium
(gas), and 70% dark matter.

However, in my opinion, the mass of stars in a galaxy may be
substantially underestimated, because the mass-luminosity relationship
(which is used to derive the mass) is quite inaccurate for low mass
stars (1 solar mass). If you look at the diagram in
http://sim.jpl.nasa.gov/scienceMotiv...ence_henry.pdf
, you can see that for stars between 0.3 and 1 solar masses, the
actual luminosity is higher up to about 2-3 stellar magnitudes (i.e.
up to a factor 10) than that implied by the mass-luminosity
relationship. And since according to the mass-luminosity relationship
10 times the luminosity means twice the mass, 10 times as many stars
with half the mass would result in the same overall brightness but 5
times the overall mass. So if there are a lot more low mass stars than
generally assumed, this could lead to a severe underestimation of the
total mass as calculated over the presently used mass-luminosity
relationship. Obviously, this could have a significant bearing on the
'dark matter' assumption.

Thomas

In article , Thomas Smid
writes:

I found these figures through Google:

Our Galaxy, like most well-studied spiral galaxies, chiefly consists
of stars, gas, and dust. Studies of its visible disk indicate that
most of the mass is in the stars, with only about 2% gas (mostly
hydrogen) and about 0.01% dust.

and

Composition of a cluster is 10% galaxies, 20% intracluster medium
(gas), and 70% dark matter.

Either one accepts evidence for (non-baryonic) dark matter, or one does
not. If one does, then one should include it in the tally for
well-studied spiral galaxies (which were the first indicators of dark
matter, via their flat rotation curves, IIRC).

In article ,
Phillip Helbig---undress to reply writes:
Either one accepts evidence for (non-baryonic) dark matter, or one does
not. If one does, then one should include it in the tally for
well-studied spiral galaxies (which were the first indicators of dark
matter, via their flat rotation curves, IIRC).

I think the first evidence was velocity dispersions of galaxy
clusters (1930s). Spiral galaxy rotation curves were much later
(1960s?). Nowadays, there are many lines of evidence, which is why
it's called the "concordance cosmology."

A very recent paper
http://www.nature.com/nature/journal...ture09578.html
suggests that the stellar mass function may be more "bottom heavy" in
elliptical galaxies than locally in the Milky Way. If this is
correct, more baryonic dark matter resides in stars and less in
intracluster gas than now thought, but the ratio of baryonic to
non-baryonic matter would not be affected.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

In article , Steve Willner
writes:

In article ,
Phillip Helbig---undress to reply writes:
Either one accepts evidence for (non-baryonic) dark matter, or one does
not. If one does, then one should include it in the tally for
well-studied spiral galaxies (which were the first indicators of dark
matter, via their flat rotation curves, IIRC).

I think the first evidence was velocity dispersions of galaxy
clusters (1930s). Spiral galaxy rotation curves were much later
(1960s?).

Right. It was Zwicky who pointed out that luminous matter in galaxy
clusters is not enough to keep them bound. On the other hand, I'm not
sure that, at the time, it was clear that they were bound, so spiral
galaxies (rather obviously bound) are probably more convincing.

Nowadays, there are many lines of evidence, which is why
it's called the "concordance cosmology."

Indeed.