Cluster Intergalactic Gas Heating & Cooling Problem

  1. This is an interesting subject. There have been discovered very large (up to around 100 kpc) hot (10^7 K) intergalactic gas clouds within galaxy clusters.

    A simple calculation based on the density of the gas clouds in question and the emission rate of the hot gas shows the gas clouds should have cooled and formed stars/galaxies.

    There are two anomalies. What is the source of energy to heat a very large gas cloud evenly. As noted in this paper AGN and gas in flow will heat the gas cloud unevenly. Also in the case of a gas flow hypothesis there is a mass problem as one needs too much infall gas to continually flow into the original gas cloud.

    The second and related problem, is why does the gas cloud not cool.

    Interesting also is the mass of the intergalactic cluster gas is approximately the same as the mass of the visible matter (stars) in the cluster's galaxies.

    Last edited: Aug 13, 2010
  2. jcsd
  3. One proposed solution to the cluster intergalactic gas heating and cooling problem is AGN hot gas emission.

    There are two problems with that solution. 1) The AGN hot gas will not evenly heat the intercluster gas and 2) there are no AGN in the local universe and there are clusters with very hot intergalactic gas in the local universe.

  4. The other main source of gas heating is supernovae. This is a feedback effect. When gas density increases, it cools (metal lines, radiative cooling) allowing stars to form. Collapse is then halted by SN blasting heated gas back into the cluster environment (but still bound to the halo), quenching the cold gas reserves required for star formation.

    AGN are (I think) a somewhat more inefficient heating mechanism, but both modes of Intracluster Medium (ICM) heating are required to match model luminosity functions to those observed - SN for the faint end and AGN for the bright end. The cluster gas is in fact the dominant baryonic mass component in a cluster (I think Voit 2005 is a ood review here)

    The X-ray emission of the cluster gas does not arise from the AGN itself, more the high election densities (thermal bremstrahlung) arising from large graviation potentials.
  5. Hello Dnam,

    Thanks for the Voit 2005 reference. His review paper is a good summary of issues related to clusters.

    Voit noted that the cluster gas mass is significantly greater than the mass of the stars in the cluster.

    Fabian estimates the cluster gas to be six times the mass of all of the stars in the cluster galaxies.

    As clusters seem to be closed boxes that would imply a significant portion of the galaxies' gas is ejected back into the intergalactic space.

    Both Voit and Fabian invoke AGN heating as a possible explanation to heat the cluster gas. They note however AGN heating does not heat the gas evenly and cannot hence explain the observations. (AGN heated cluster gas will cool in one section and heat in another.)

    There are other constraints on the quasar/AGN mechanism that is required to explain observations. I will start a separate thread later this fall. For example, AGN must also be cyclically active to explain the observations based on the classical BH model with an accretion disk to explain the evolution density of quasars per comoving region of space with redshift. (The explanation that a classical black hole is heating the cluster gas due to periodic in fall of gas in the black hole.)

    They provide no explanation as to what could cyclically cause gas to fall into the BH in addition to problem that AGN will heat the gas unevenly.

  6. It is very interesting topic. Interesting also is the mass of the intergalactic cluster gas is approximately the same as the mass of the visible matter (stars) in the cluster's galaxies.
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  7. Actually, the mass of the gas is approximately 5-10 times the mass of the stars in a cluster! Also, a large fraction of the stellar light coming from clusters (maybe 20%) comes from intracluster stars which are no longer part of a galaxy.
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