wacky ionization states

At Galaxy Coffee, Ben Oppenheimer (the Leiden one, not the AMNH one) gave a nice demonstration (theory) that the ionization states of metals around quasars are very likely to be out of ionization equilibrium with any radiation field, from the quasar or the cosmic mean. The reason is that if the quasar illumination varies, it can take quite a while for the atoms to cascade back to equilibrium. He treated this as a problem—complexifying interpretaton—but it also might (in some circumstances) be an opportunity, as it shows that some kinds of line ratios could be an indicator of illumination history.

Not much else happened today, although both Foreman-Mackey and Weisz spent time discussing code issues in their respective projects.

1 comment:

  1. The same considerations apply to emission lines, most notably in quasar extended emission-line regions and their relatives around milder or fading AGN. There was an old paper by Binette and Robinson starting to approach how "fossil" nebulae evolve in line ratios. Gary Ferland says that CLOUDY is set up to deal with these situations (but IIRC hasn't actually been tested for them).