Galactic Winds and The Chemical Enrichment of the Intergalactic Medium

I'm back from The Chemical Enrichment of the Intergalactic Medium workshop at the Lorentz Center (*) in Leiden. An exceptionally fine meeting, if I do say so myself, not just because there were a lot of excellent talks but also because of the relatively complete change in attitude toward galactic winds by cosmologists.

Ten years ago the common sentiment from theoretical cosmologists at the few Cosmology-related meeting I attended was that winds from galaxies simply couldn't be significant as they'd destroy the Ly-alpha forest. Arguments that (a) this wouldn't happen as winds wouldn't couple effectively the the denser-than-average gas in the forest, and (b) the metals in IGM had to come out of galaxies and we see galactic winds in action in the low redshift Universe, were ignored.

At the Leiden meeting it was rare for a talk not to mention winds in one way or another.

The argument is now not whether winds exist and are responsible for the enrichment of the IGM, but has moved onto more practical and interesting questions such as

• What type of wind is most important (supernova-driven vs AGN; mechanical vs radiation pressure; energy-driven vs momentum conserving; core collapse SNe vs Type Ia SNe)?
• What kind of host is driving galactic winds (dwarf galaxies, with massive galaxies incapable of driving winds versus powerfully starbursting but moderately massive galaxies such as the Lyman Break Galaxies; AGN hosts; BCGs; are there winds in the DLAs, despite their low SF rates; L* versus 0.1xL* galaxy hosts)?
• What is the epoch of peak IGM enrichment (weak outflows providing pre-enrichment at z ~ 6-10 versus the active winds at z~2-3, the epoch of maximum star formation and hence peak nucleosynthesis)?
  
• Do environmental effects alter the efficacy or need for winds (are winds necessary within groups and clusters, or can ram pressure stripping accomplish getting the metals out of the galaxies; is ram pressure stripping effective even in the field)?

In addition the meeting was exceptionally well organized and run, with talks running to time, discussion sessions that actually did debate and discuss interesting issues, time for self-organized work with offices provided to all attendees, and a very friendly and collegial atmosphere even when disagreements arose. Not one but two social events with free drinks (this would never happen in the US) also aided in making this one of the most memorable meetings I've been to in years.

(*) The Lorentz Center exists purely to facilitate and run such workshops, i.e. it is in some ways a European equivalent to the Aspen meetings in the US. Apparently anyone can propose a workshop, so keep it in mind.