KITP: ye olde globular clusters

we go back in time, to when the universe was young
and ponder when the globulars got made, how, why and why some are blue and some are red but very few are greenish
and we learn the globular cluster formation is not transitive
hah, and some people are impressed with mere non-commutation relations...



Jay is on deck, and he had drawn a lot of pictures.
I immediately conclude that not everything to do with globulars is monotonic or even convex.
I also conclude Jay talks faster than I can type...

  1. Bimodality
    generally see blue metal poor clusters and red metal rich(er) clusters
    usually (always as data improves) in clearly separated bimodal distribution in all massive galaxies
    Metal poor center around [Z]~ -1.5 and metal rich [Z]~-0.5 for Milky Way like galaxy
    bigger galaxies have more metal rich modal points for distribution, and vica versa for lower mass galaxies
    ie the dwarfs which made the Milky Way are not like the dwarfs we see still around out there
    so we invoke metallicity bias - dwarf galaxies that accrete early collapsed earlier and made stars earlier and got metal rich earlier than those which collapsed later to survive to today
  2. Globular cluster-galaxy relations
    n low mass dwarf galaxies tend to have only metal poor clusters, but the younger clusters also tend to appear
    blue clusters are more widely spatially distributed about the galaxy
    seen in both ellipticals and spirals - though getting down to bulge free Sd maybe not so much red clusters

    Peng et al (XV) (2008) is good ref on some of this.

  3. Globular cluster efficiency
    Old factoid: the specific frequency of globular clusters is minimum near L*
    in particular metal poor globulars have high specific frequence at low mass and at high mass - so the current ellipticals can't be made from the current spirals, because the currently surviving spirals have too few metal poor globulars per unit mass, and you can make more metal rich clusters, but not metal poor anymore
    So either spirals that merged into ellipticals knew to make extra globulars early, or a lot more smaller mergers were involved

    Also, which I had not appreciated - the scatter in the specific frequency is higher at both the high and low galaxy mass end.

  4. Spatial distribution
    blue clusters halo population
    red clusters are thick disk/bulge profile
    in ellipticals the red clusters form a core, do not follow the light cusp all the way in - destruction

    NB: we have very little data on stellar profile in outskirts of ellipticals.

  5. Mass function
    young stellar clusters follow a power law with index ~ -2
    older clusters show a break at some mass (which is a function of age???)
    is the evolved function a broken power law or a log-normal? We gots to know.
    is the breaking of the cluster mass function due to internal processes or external processes
    We think we must consider binary clusters and how and when and if they merge and then what? Seriously, make a good paper



Formation:

    Make blue clusters between z=10-3?

  • Are they mini-galaxies(nuclei) - ie did they form in dwarf dark matter halos
    ie are all (almost all) globulars like M54 - actually nuclear clusters of dwarf galaxies,
    if so, where is the rest of the galaxy for most of them - can we see the traces
    should we see the dark matter halos
    does this work for metal poor globulars only
    do you get the mass function right?
    where does the angular momentum go? - expect to make fluffy ~ 100pc structures
    where is that dark matter halo?

    parsimony: how are the red globulars made?

    yet there is M54... and of course Ω Cen
    M54 is clearly embedded in a dwarf galaxy center; Ω Cen looks like it ought to be in the middle of a galaxy, but isn't (and lets not forget G1)...

  • Fall and Rees scenario
  • Form as baryonic structures when disks form and in mergers
    - clearly some do? Metal rich only? mostly?

    Do any of these scenarios get rh right?



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I'm sorry I missed the discussion this morning... Not sure if it was mentioned, but Simon has worked on binary star clusters. For example:

http://arxiv.org/abs/astro-ph/0609061

And I'm sure Enrico mentioned the work he's done on the relationship between merging clusters and mass segregation.

By John Fregeau (not verified) on 05 Mar 2009 #permalink

Re Globular cluster efficiency:

From http://adsabs.harvard.edu/abs/2008ApJ...681..197P

"GC fractions of low-mass galaxies exhibit a dependence on environment. Nearly all dwarf galaxies with high GC fractions are within 1 Mpc of the cD galaxy M87, presenting the first strong evidence that GC formation in dwarfs is biased toward dense environments"