DM-Baryons

Since the announcement was only a month ago, perhaps it is worth noting the recent further evidence for dark matter. -Marty

An interesting question is whether we can ever Disentengle the traditional assumption of DM and assumption of GR: Wouldn't it be better if we could check the two independently? Is itreally necessary to believe einsteinian gravity before we can talkabout DM? Since it is hard for physicists to prove GR outside the solarsystem, can we astronomers ever prove DM with GR unproven? What isamazing to me is that recent data suggest that WE CAN: the bulletcluster and several galaxy-QSO strong lenses have recently made thecases for DM in theories more general than einsteinian. As found inbullet cluster, there are direct evidences for dark matter actually forgalaxy-sized lenses as well. e.g., there are a number of ellipticalsstrong lenses with abnormally high M/L (table 3 of http://www.blackwell-synergy.com/doi/full/10.1111/j.1365-2966.2006.10023.x). The abnormal M/L happens for both GR and Alternative Gravity (theirfig 16). So the need for DM is finally less dependent on belief ofEinstein's theory. Angus et al found the same with the bullet cluster (http://arxiv.org/abs/astro-ph/0609125), again non-baryonic material (either mundane neutrinos or somethingmore exotic) is needed both in GR and in Alternative. So the Bullet isnot atypical and seems in agreement with galaxy scale strong lenses. -H.S. Zhao

Related discussion: Thurs 28 Sept, 9:30am, courtyard - exploring first light with lensing

One of the topics which it might be good to discuss during this KITP workshop is using gravitational lenses to search for first light in the universe. (i.e. using gravitational telescopes such as rich clusters to look for galaxies at extremely high redshift, which might host the first generation of star formation, or those UV sources such as star forming galaxies and AGN which may have been responsible for reionizing the Universe).

Possible discussion topics

1) Are the lens models for clusters good enough to recover the luminosity	function of the most distant lensed sources? 2) Do you win by looking at lensed regions (in terms of efficiency of	finding high-redshift galaxies) compared to a shallower but larger-volume survey 3) To see the first stars and supernovae from Pop III, what lensing        amplification would be required with current and future telescopes         (e.g. JWST) and is such high magnification predicted         anywhere? 4) What are possible techniques to identify high-redshift lensed galaxies (blank-sky spectroscopic searches; photometric redshifts;        radio) 5) What can we say about reionization (and the HII regions of         galaxies) from lensed sources -	what redshift, and what is responsible?

If you are interested in any aspect of this, could you drop me a line. I would like to organize a short (40minute) discussion Thurs 28 Sept at 9:30am in the courtyard (note early start!), and a second follow-up meeting next Monday 2 Oct. All welcome - anyone with experience of strong lensing models (particularly clusters) in particular!

Andy Bunker

ORGANIZATIONAL NOTE

Friday's meeting is at 2pm in the Ocean Tower.

Your homework is to submit a paragraph (to Draft Proceeding DM - People's interests) that explains both your current/past interests in the questions related to the DM-baryon connection. You should also add questions you have about this topic - feel free to be provocative!

Contribute also to the "Proceedings" via the link below.

-Dennis

Draft Proceeding DM-Baryons

Please contribute to the above linked pages.