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Origin of the intracluster medium

  1. Sep 24, 2004 #1

    hellfire

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    In this recent press release,

    "Chandra turns up the heat in the Milky Way center"
    http://www1.msfc.nasa.gov/news/news/releases/2004/04-169.html

    it is described the observation of heated gas at a temperature of 100 million K at the center of the Milky Way. It seams to be still an open question which source could had heated the gas to such a high temperature. But there is also still another mystery: the gas seams to be continuously regenerated, since due to its high temperature the whole gas cloud should had escaped gravity within a small fraction of the lifetime of the galaxy.

    The intracluster gas is postulated to contain a significant fraction (apart of baryons in galaxies) of the baryonic mass in galaxy clusters. As far as I know, two theories are postulated to explain its origin: (a) the intracluster gas was already there before galaxy formation (primordial gas) and was then compressed into the potential wells of galaxy clusters recently, during cluster formation, or (b) the intracluster gas contains mainly already processed gas, which escaped from galaxies.

    The option (a) is supported by the evidence of clusters with an extremely large intracluster gas mass (up to six times the stellar mass of galaxies) and, as fas as I know, with the models of biased galaxy formation, which postulate that the efficiency of galaxy formation was not high. The option (b) is supported by the observation of high metallicities in the intracluster gas.

    Probably, the truth lies somewhere in the middle between (a) and (b).

    But, my questions now. Both hypothesis assume different heating mechanisms of the gas, but it seams that both mechanisms (or both sets of mechanisms) lead to the same temperature (between 10^7 and 10^8 K). Is this correct? Or is the gas ejected by galaxies colder and additionally heated afterwards e.g. due to compression by falling into the potential well? If not, how is such a coincidence possible? On the other hand, which fraction of the intracluster gas could have been originated in galaxies? Could such an observation (as mentioned above) be relevant for testing theories of the formation and origin of the intracluster gas?
     
  2. jcsd
  3. Sep 24, 2004 #2

    Nereid

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    Excellent questions hellfire!

    Going entirely from memory (a few hours with Google's help would no doubt show ~>30% of my memory to be, shall we say, off the mark), some quick comments:
    - the intracluster gas certainly contains reprocessed material, from SN in galaxies, from starburst clusters, from gas stripping of gas-rich galaxies (from collisions), and more
    - it also probably contains significant amounts of primordial gas
    - the role of galactic magnetic fields in confining all but the 'hottest' plasmas (cosmic rays) to the galactic halos is pretty much unknown
    - cooling flows are pretty well-established from X-ray observations (this suggests a high primordial content)
    - there was a good article in a recent Scientific American on gas clouds in (or near) the Milky Way halo (well, above the plane anyway); the authors concluded that most of the clouds seemed to be re-processed material (not primordial). Of course, how relevant these findings are to intracluster gas in general is quite an open question
    - there was an interesting result (announced via a PR) from Chandra work last year (?), intracluster gas heating due to SMBH in the cD core galaxies 'blowing bubbles', i.e. acoustic heating :cool:
     
  4. Sep 24, 2004 #3

    Garth

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    Dr Greg Bryan (Oxford) gave a lecture at the RAS on 9th January 2004 – "The Impact of Galaxy Formation on the Intergalactic Medium " Precis:-'Galaxies at low and high-redshift are observed to drive winds, polluting the space between galaxies with both energy and heavy elements. Simulations are used to investigate if the effect of these winds can be seen in one our best probes of the intergalactic medium: the absorption lines seen in spectra of distant quasars usually known as the Lyman alpha forest.'
    He demonstrated how only 20% of the intergalactic metallicity was caused by galactic outflow. Does this mean the other 80% is primordial?

    In which case might this mean the intergalactic gas and the metallicity came out of the Big Bang? Just a thought - Garth
     
  5. Sep 25, 2004 #4
    Last edited: Sep 25, 2004
  6. Sep 26, 2004 #5

    Garth

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    Thank you for that link, of course the Bryan lecture was a decade later and presumably took the Trentham conclusions into account. It seems that Bryan was going back to the earlier conclusion, " While Matteucci & Vettolani (1988) recovered the total ICM iron mass, one of their primary conclusions was that the winds could only contribute at most 10%20% to the total gas mass the bulk of the gas was necessarily of primordial origin."
    Interesting..
    Garth
     
    Last edited: Sep 26, 2004
  7. Sep 26, 2004 #6

    turbo

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    Given the metallicity of the gas, and our model of how heavier elements are formed in stars, it might be hard to characterize the gas as primordial, unless it was injected into our universe via some mechanism like Smolin's black hole=universe model.

    Here is a nice source of reference materials and a reasonable overview of the field. In summary, the paper says that the observed dwarf galaxies are insufficient to provide the ICM, and that ~65% of it is primodial. I'm sure that there are opposing views.

    http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v475n1/34360/sc1.html
     
    Last edited: Sep 26, 2004
  8. Sep 26, 2004 #7

    Garth

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    The freely coasting model predicts the metallicity is primordial.
    That is the same as meteor's link before!
     
  9. Sep 26, 2004 #8

    turbo

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    Duh! Sorry for that. I had been plowing through CiteBase (chasing referring papers and paper referred to) and came full-circle. I have a half-page URLS for papers, each with a one-line note to myself, and I pasted that one in before heading out for a ride.
     
  10. Sep 26, 2004 #9

    turbo

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    Here is a very recent paper by Nagashima et al. In summary they conclude that very massive galaxies with very rapid production of very massive stars are required to supply the metalicity of the ICM. In addition, the initial mass function must have been much higher (top-heavy) in these galaxies. Such starburst activity would not easily go unnoticed - do we see enough of these very bright collisions to fit with this model?

    http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/0408529

    Here is a paper by Kroupa arguing that the IMF is uniform, and questioning the variable IMF used by some to explain the metalicity of the ICM while staying within the confines of the Heirarchical Model.

    http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/0201098
     
    Last edited: Sep 26, 2004
  11. Sep 27, 2004 #10

    Garth

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    The Hubble ultra deep field https://www.physicsforums.com/showthread.php?t=44419 seems to indicate the very earliest galaxies were smaller than required, even to ionise the intergalactic medium, let alone seed it with metallicity.

    It seems to be a problem later too, only about 20% can be explained by visible galaxies.

    Garth
     
  12. Sep 27, 2004 #11

    turbo

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    Yes, it is a challenge to the hierarchical model. Stars and groups of stars form and gravitate into clusters, form smaller galaxies, that merge into larger galaxies. The emphasis on smaller galaxies in the early universe in the hierarchical model seems to run counter to the view that mergers of large galaxies with high initial mass functions are necessary to provide the observed metalicity. Primordial metalicity could be more easily explained by a steady-state universe as opposed to a SBB model.
     
  13. Sep 28, 2004 #12

    Garth

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    Or by the freely coasting model, which predicts the same (order of magnitude) primordial metallicity as that which is observed in the IGM.

    Garth
     
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