2006-04-03

LHC, clustering, and weak lensing

There were two talks on the LHC today, one by Jenni (CERN) on the ATLAS experiment, in which NYU is about to become a partner, and the other by da Costa (Harvard) about the top. I embarassed myself by asking about the uncertainty principle: Unlike astronomers with photons, high-energy experimentalists do not try to detect particles at the fundamental limits of precision. Of course such precision would be insanely expensive (and these machines are expensive enough already). But in both talks, the LHC came across very well; I am very excited about it.

In group meeting, Molly Swanson (MIT) discussed her work on mangle (a toolkit for the description of piecewise constant functions on the sky using spherical polygons) and some very nice results on linear relative bias among different galaxy populations. She showed that linear bias is a pretty damn good model, even on few-Mpc scales!

Sheldon, Masjedi, and I discussed features in the weak lensing signal around LRGs that Sheldon is convinced (probably rightly) are evidence of significant systematic errors. But the error is hard to find and I got to wondering if the result could be real. It could be if a significant fraction of LRGs are tens of kpc from the centers of their dark-matter halos. Is that insane? Surely galaxy formation models would tell us if it were true? Time to call in the theorists.

1 comment:

  1. I would modify your last statment
    slightly: I think they would all
    have to systematically be located
    at nearly the same radius from
    the center of mass to get the
    shape I see rather than just
    randomly displaced which would
    just convolve the signal.

    There is another killer for that
    which is that the shear on 20kpc
    scales would not be so high due
    to the lrg; that level of shear
    could only occur on much smaller
    scales. This is because the
    galaxy is off from the center
    of mass so cluster isn't
    contributing much to the shear.

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