average image, does environment matter?

Actually started up the average image slash quasar–photon cross-correlation code today. It runs. Does it give good answers? I don't know because it is incredibly slow. Ah well, if only I knew a good programmer!

Schiminovich and I spent time talking about religion and politics and then a bit about galaxy environments, in particular the resolution of the debate between Jacqueline von Gorkom (Columbia) and myself about whether environment matters to galaxy evolution. Being a stickler, Schiminovich objected to that characterization of the issue up-front. But I think we almost agreed that environment has its strongest effects on galaxies near the centers of clusters and merging galaxies. These systems make up only a percent or so of the galaxy population in the last few Gyr, so although environment matters deeply to these galaxies, they are a trace population.

We certainly know about environment effects on the bulk of galaxies, but it is straightforward and relatively uninteresting: At fixed mass (or other properties), the most important environmental effect is on the specific star-formation rate. But we know from statistical tests that environment affects this very slowly or very indirectly, probably by heating the interstellar medium (slowly, not generically in rapid bursts or events, which are extremely rare). So I think there is a consensus position possible: Environment matters, but a small amount to a large fraction of galaxies and a large amount to a small fraction.

1 comment:

  1. nice post....but did you know
    In our world today around 2.5 billion people do not have access to improved sanitation and some 1.2 billion people do not have access to an improved source of water.

    So environmental changes does affect the human beings...