#cosgal16, day 1

Today was the first day of the Cosmic Dawn of Galaxy Formation meeting in Paris, organized by Charlot and a cast of many. The meeting is not in any area I work these days, so I learned a huge amount. In general I find it very rewarding to go to meetings outside the areas in which I work. So much happened I can't possibly mention it all, but here are a few highlights:

Oesch showed redshift 10 and 11 galaxy population estimates. And along the way, showed full 2-d modeling of the 3DHST grism spectroscopy images. I am impressed by how good this looks, and this was shown again by other speakers. McLure pointed out that much of the disagreement about luminosity functions at redshift 10-ish are really disagreements about how the data should be presented; there isn't nearly as much disagreement at the data level. This is a pet peeve of mine: Often debates happen at punchline level, or in the latent space, when the only points to argue about live in the space of observables.

Treu and Smit both spoke about using lenses to find very high-redshift sources. In answer to a question from me about reliability of galaxy population statistics given observations of highly magnified sources, Treu emphasized that once you have highly magnified sources, the lens model is very strongly constrained. That said, he emphasized that the volume as a function of magnification is not well constrained at high magnifications. Smit showed that at finite angular resolution, naive interpretations about galaxy emission processes depend strongly on resolution. She could make this point securely because (with lensing) she has multiple views of the same galaxy, at different angular magnifications.

Ocvirk and Wise and Beckmann all spoke about insanely large computational programs to simulate high-redshift galaxies. The first two each had tens of millions of CPU+GPU hours on national facilities! Ocvirk talked about tracking the radiation along with the matter, which is a hard problem (and, indeed, even with 7 million hours per run they are only doing the fluid approximation). Beckmann talked about tracking the accretion onto black holes, by adaptively refining the hell out of the simulations around seed black holes. She finds (numerically) that the BHs are thrown from the halos at early times and has to add drag to keep them in. Apparently there is a history of doing this in simulations, but it sounds a tiny bit suspicious to this (untrained) outsider.

In side conversation, Chuck Steidel (Caltech) asked me a good question: Do any of the APOGEE stars have such high alpha-to-iron that they could be understood with pure core-collapse nucleosynthetic origins? That's worth checking out.

1 comment:

  1. Last time Gail Zazowski gave a webinar here I asked her about Alpha/Fe in bulge APOGEE stars - spheroidal, hence Early-type galaxy abundance like? So I hoped. I remember she answered that there was nothing special about their abundance ratios. But certainly worth checking.