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Galaxies in filaments; a different evolution?

  1. Dec 9, 2007 #1
    Might galaxies in filaments http://pil.phys.uniroma1.it/twiki/bin/view/Pil/GalaxyStructures and deep in voids have a different evolution from that of galaxies in clusters? One has a tapestry of superclusters (clusters of clusters) and of larger voids; with filaments leading(?) into rich clusters. How might one distinguish any differential evolving history of galaxies in filaments or voids vs in clusters? If there were late formation of most of mass of galaxies in filaments/voids, might they have more gas, and thus more star formation i.e. star burst and more emission lines? Would there be less dark matter (DM) http://en.wikipedia.org/wiki/Dark_matter in galaxies in filaments/voids? How would one ascertain this? By extent/lack of flattened rotation curves http://en.wikipedia.org/wiki/Rotation_curves for spirals? An extented flattened curve means more DM further out; the original discovery route of DM.
  2. jcsd
  3. Dec 9, 2007 #2


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    Try the WMAP3 release, they discuss this kind of thing to great lengths.
  4. Dec 9, 2007 #3


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    Galaxies in clusters are, in fact, known to have different properties than galaxies outside of clusters. For example, cluster galaxies tend to be redder in color, have less gas, and be more elliptical shape than the average galaxy in the universe.

    It has long been assumed that filaments end at clusters and I recently verified it in my thesis work (with caveats I won't get into here).

    Evolution is difficult to track directly because we don't have particularly good statistics for galaxies at high redshift (early times). We can look at the mean properties of galaxies in these environments and compare them to those found at the present time. Such studies yield the results I mentioned above. The "filament" environment turns out to be difficult to define, so there is still work to be done.

    Astronomers will sometimes attempt to model star formation histories of galaxies by looking at the stellar populations (that is, with "population synthesis"). Emission lines can tell you whether or not the galaxy is actively star-forming at the epoch we observe it, but tell us nothing of how long it has been doing so. Population synthesis is a tricky business, so we're often better off trying to observe high-redshift star-forming galaxies directly. Fortunately, star-forming galaxies are easier to find at high redshift than their quiescent cousins, so the star formation history of the universe has, to some extent, already been studied this way. It seems to peak at around z ~ 1.5 - 2.

    Relative to a galaxy of the same mass? I'm not aware of any such trend, but then the mass is usually dominated by the dark matter anyhow.

    The technique for measuring rotation curves does not in any way depend upon the galaxy's environment. One could also use gravitational lensing, velocity dispersions, etc. The former measurement can sometimes depend on environment because nearby structure can contaminate the lensing signal.
    Last edited: Dec 9, 2007
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