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...
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
- 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.
- 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.
- 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.
- 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
- 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?
Make blue clusters between z=10-3?
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:
And I'm sure Enrico mentioned the work he's done on the relationship between merging clusters and mass segregation.
Re Globular cluster efficiency:
"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"