2007-07-10

faint-source astrometry, cluster stars

Discussed with Jester the issues of measuring and detecting faint sources in multi-epoch imaging, especially sources too faint to be detected well at any individual epoch. It seems that these problems are not currently solved, although they are relatively simple statistics problems.

Discussed with Romeel Davé (Arizona) some issues of stellar baryons and dark matter in massive collapsed objects. If massive objects (like clusters and groups of galaxies) have formed through many mergers, and if some of the major mergers follow star formation (as we think they do), then in general it is hard to avoid having the sum total stellar mass distribution (including galaxies and intragroup light) trace the dark matter (in azimuthal average). That's a serious prediction! Testing it may require sharpening some blunt tools. But Sheldon, Blanton, and I have started down this path for other reasons.

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