# Density of the inter-cluster medium

1. May 30, 2005

### Garth

That is interesting ST. How dense is the inter-galactic-cluster medium?
Garth

Last edited: May 30, 2005
2. May 30, 2005

### Nereid

Staff Emeritus
This is a great question Garth ... and if I may add a rider: and how is such density measured/inferred?

If you don't mind, I'd like to keep this thread to just QSO absorption lines (and closely related topics) - May I split this off as the start of a new thread?

3. May 31, 2005

### hellfire

WHIM stands for Warm-Hot Intergalactic Medium, a low density phase at 105 - 107 K, mainly located in the filaments and not part of any virialized system. About 30% - 40% of all baryons of the present universe (z < 2) were assumed to reside in this phase. It was postulated here and there is some observational evidence in the meanwhile.

Last edited: May 31, 2005
4. May 31, 2005

### SpaceTiger

Staff Emeritus
There are two main components to the intergalactic medium, the cold component (T<105 K) and the warm-hot component (105-107 K). The former is only a few times the critical density:

$$\rho_c=\frac{3H^2}{8\pi G}$$

corresponding to a density of about 10-5 cm-3. The warm-hot component is about a factor of ten more dense than this. Finally, intracluster gas has densities of order 10-3 cm-3 and temperatures of around 107 K.

You can determine these conditions from a lot of things, including fitting absorption lines in quasar spectra, looking at X-ray emission and absorption, and the Sunyaev-Zeldovich effect.

Last edited: May 31, 2005
5. May 31, 2005

### Garth

These densities seem very high ST - with the critical density at around 10-29 cm-3?

Garth

6. May 31, 2005

### SpaceTiger

Staff Emeritus
That's 10-29 g cm-3. I was quoting densities in terms of atoms per unit volume (instead of mass per unit volume).

7. May 31, 2005

### Garth

Doh!!
Homer

Sometimes I just read too fast for my brain to catch up with my eyes.

ST what's that in real money? i.e. in terms of gms.cm-3 and as a component of Omega?

Garth

Last edited: May 31, 2005
8. May 31, 2005

### SpaceTiger

Staff Emeritus
The cold component corresponds to, as you said, about 10-29 g cm-3. The other two are a factor of 10 and 100 larger, respectively.

In terms of omega, it depends on the redshift you're referring to. I don't know the numbers off the top of my head, but I'll look it up later.

Last edited: May 31, 2005
9. Jun 1, 2005

### Nereid

Staff Emeritus
10. Jun 1, 2005

### Garth

Thank you Neried.

The first question is that of the inventory of the IGM and the contribution it makes to the total Omega density parameter of the universe; that is both of baryonic and non-baryonic dark matter.

We have cold gas clouds that leave the Lynman forest imprint on distant quasar spectra, WHIM (Warm/Hot Intergalactic Matter), primordial or otherwise Black Holes and any member of the exotic particle zoo that you care to dream up! Anything else I have forgotten? Ah yes! and a Dark Energy contribution; any way of measuring this?

Garth