Intergalactic doldrums - flotsam and jetsam

[Loren Booda]

What types of substantial debris might we expect to find in intergalactic space - dark matter mostly? Although that region supposedly posseses close to near-vacuum, don't you think it would harbor ejecta from neighboring galaxies or material from the pregalactic era?

 

[meteor]

I don't expect many surprises. The primary composition of these zones is the intergalactic medium, a gas composed principally of hydrogen and helium, and the IGM is highly ionized, although there exist clouds of non-ionized atoms. The IGM can be divided in diverses zones, for example the Warm-hot intergalactic medium
http://arxiv.org/abs/astro-ph/0007217

 

[Loren Booda]

Why no tangible intergalactic matter?

 

[hellfire]

I don't expect many surprises. The primary composition of these zones is the intergalactic medium, a gas composed principally of hydrogen and helium, and the IGM is highly ionized, although there exist clouds of non-ionized atoms. The IGM can be divided in diverses zones, for example the Warm-hot intergalactic medium
http://arxiv.org/abs/astro-ph/0007217

I read in the abstract that this gas is not part of virialized objects. Therefore I assume that it is not inside of galaxy clusters.

If I recall correctly, the baryon fraction inside galaxy clusters is assumed to be nearly the same as the baryon fraction in the universe (Omega_baryon / Omega_m), at least for low redshift values.

This seams not to be the case, especially if 30-40% of baryons are outside of clusters. Does this mean that the baryon fraction of clusters is less than Omega_baryon / Omega_m?

Regards.

 

[Nommos Prime (Dogon)]

Superheated "Galactic Shroud" Gas

How short our memory is...
What about all the Superheated Gas surrounding our Milky Way and (I claim) ALL other galaxies?

I'd reckon it accounts for at least 70+/- % of ALL Dark Matter;
http://www.nrao.edu/pr/2002/mwclouds/

 

[meteor]

Oh yes, there's superheated gas around the Milky way, the origin of this gas is explained by the Galactic fountain theory:
http://www.jhu.edu/~gazette/2000/jan1800/18fuse.html
"The finding supports the "galactic fountain" theory, which suggests that supernovae blow hot gas outward in all directions, but because there's less material above and below the plane of the galaxy, the gas can expand farther in these directions and create a bubble above or below the galaxy."

but I'm not sure if the density of this gas is very different from that of the IGM. Do you know?

 

[hellfire]

I have read a little bit about this without reaching a clear understanding of the situation.

I am not sure whether the existence of a warm or hot IGM (or warm-hot IGM) as described in the paper referenced by meteor is widely accepted.

I believe there are some established estimations of the baryon fraction in the universe based on the assumption that the baryon fraction inside galaxy clusters is representative for the universe as a whole. A hot IGM with 30-40% of baryons would question this estimations.

Anyway, postulating such a medium not beeing part of virialized objects (clusters) but having a high temperature (10^5 – 10^7 K), leads to the question of which source produced the high temperature of the gas.

Also, the question is whether this hot IGM would or would not contribute substantially to the diffuse x-ray background.

I think the hypothesis of IGM contribution to the x-ray background was already discarded due to inconsistences with the nucleosynthesis in the hot big-bang (?) and it was accepted that the x-ray background was mainly generated by discrete sources.

May be someone could give some insight.

Regards.

 

[meteor]

I'm afraid that I can't give you an answer, because I'm clearly not at your level of knowledge hellfire, but I found this quote that can be of utility
http://nedwww.ipac.caltech.edu/level5/Sept03/Firmani/Firmani3.html
"Cosmological simulations including gas show that at z = 0 only 30 - 40% of the universal baryon matter is within collapsed halos; the rest is in the form of warm-hot IGM in the filaments and voids (Davé et al. 2001). Recent observations tend to confirm this prediction (e.g., Manucci, this volume). Not all the gas trapped within the galactic halos ends up in the central galaxy: for large halos (M 1012 M) the cooling time may be longer than the Hubble time, while for small halos (M 1010 M) a large fraction of gas may be expelled due to feedback."

 

[Nereid]

There was a good Scientific American article recently on the IGM near the Milky Way, if you can get a copy, it's worth the effort.

The quick answer to Dogon is 'because gravitational lensing says there's far more mass than is detected by all other means - radio, IR, optical (e.g. absorption), X-ray, cosmic rays), oh and the relative abundance of primordial nuclides is consistent with other estimates of baryonic mass.'

To answer Loren ("Why no tangible intergalactic matter?"), there's surely some - the fountains meteor refers to (which are very real; if I get time I'll post some links to some very nice piccies of these) will carry dust grains out into the IGM, for example. However, there can't be much, otherwise there'd be 'intergalactic reddening', for example. Some time ago there was a minor controversy about the dust content of spirals; IIRC, the matter was settled with some very nice Hubble obsevations of spirals backlit by distant ellipticals (the wavelength-dependence of the opacity - 'optical depth' - set tight limits on the *total* amount of intervening dust).

Almost all the 'diffuse X-ray' background is (apparently) accounted for by known objects (e.g. dark quasars and other AGN, distant clusters), per a recent Newton-XMM result (check out the ESA website for more details), so no need to worry hellfire!

There's still a lot to learn about the IGM, including its heat sources - did you see the (Chandra?) result, about AGNs blowing giant bubbles, which generate enormous acoustic energy? Too, there are AGN jets - the energy that doesn't go into EEv cosmic rays gets dumped into the IGM; some nice VLT (IR) observations of these 'hotspots'.

 

[meteor]

There're also the recent discovery of dark galaxies (galaxies without stars)