meeting is over, what did we learn
first: don't wear "city socks" in ski boots - first day out I forgot to switch to high wool socks and I have the most amazing line of blisters on my left calf...
totally awesome skiing though
good meeting also, I gather all the talks will be online soon, will post pointer when it does
two further things that interest me, and my apologies to all the talks and topics I didn't mention...
first, there is the issue of reionization - did it come early, starting at redshift 10-15, as some of us think it must, or did it come late with rapid reionization between maybe redshift 6-9? either way, where did the blue photons come from? since only small fraction of the baryons is in bound objects, you need lots of uv photons per hydrogen atom in structure - so it must be either massive stars or accreting black holes - but you need the light to come out blue, not IR or x-rays
secondly, my ex-student, Britton, presented our recent prelim results on high redshift star formation - we're looking at three modes of star formation in the early university, the first stars, regular star formation, and an intermediate phase where the combination of metallicity and microwave background ambiance regulates fragmentation - he may be onto something interesting there. lots of fun implications if true, we'll have more to say on that
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Britton's talk was very nice. I really appreciated how well he explained the physics, though it did remind me of a question I had, which is whatever happened to H2+?
Andy's point about the high EW's of Lyman alpha in many z~6 sources does point out that there maybe a lot more UV photons per baryon then one would normally predict from standard stellar populations.
H2+ is in there, as is H3+ and HD and so on and so forth.
You'd think chemistry of just H and He would be simple, but no...
Yes, primordial chemistry can be very tough, particularly at high densities, above say 1e14cm^-3. The full list of non-eq chemistry in modern sims of PopIII.1 star formation is 12 species long, and a bare minimum model requires coverage of 16 orders of magnitude in density. You end up with a set of several dozen coupled rate equations, some of them tetrationally dependent on temperature and abundances, and none of those quantities can be properly separated from any other one. (For instance, for every H2 you form, you get 4.48 eV of energy back into the gas. If you're around 2000K, that'll change the H2 formation and destruction coefficients. Now you'll probably lose some temperature, bringing you back to the starting point. Integration becomes very difficult...)
To really model the star formation problem as opposed to the collapse and fragmentation of primordial clouds you need to go up to significantly higher than that, where the chemistry gets really interesting and you have to move to a tabulated equation of state because the kinetic rate coefficients method is simply no longer valid.
Britton's work is pretty awesome, particularly with extending the cooling model but also with the coupling of different chemical models before and after stars form, and the fragmentation classification and quantification he is doing is really quite essential, especially moving forward.
Brad, thanks for the compliment on the talk.
I'm very excited by what's to come in this area. There is a rich parameter space to study with different abundance patterns, radiation backgrounds, and more realistic initial conditions (starting from supernova blastwaves, for example). One way or another, there was a transition from the first stars to the stars observed today, and I really doubt it was just an abrupt jump from one to the other. I think whatever we find is bound to be very interesting.
I'm also very excited about the things that Matt's new analysis tool will allow us to do. Stay tuned for awesomeness.
"we're looking at three modes of star formation in the early university"
Are we talking about rush week, or the whole first month of a freshman's studies?