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Concepts of Optimality and Their Uses
Lecture to the memory of Alfred Nobel, December 11, 1975allocation of resources;
Gravitational Lens Time Delays in CDM
In standard CDM halo models, the time delay of a gravitational lens is
determined by the cold baryon mass fraction, f, of the visible galaxy relative
to the overall halo. The observed time delays in PG1115+080, SBS1520+530,
B1600+434 and HE2149-2745 give Hubble constants consistent with the HST Key
Project value of H0=72+/-8 km/s Mpc only if f>0.2 (1-sided 68% confidence),
which is larger than the upper bound of fmax=Omega_b/Omega_0=0.15+/-0.05
estimated from the CMB. If all available baryons cool and f=fmax then the time
delays imply H0=65+/-6 km/s Mpc (95% confidence). If local inventories of cold
baryons, f=0.013/h70, are correct, then H0=52+/-6 km/s Mpc and the halo
parameters closely match isothermal mass models. Isothermal models are also
consistent with strong and weak lens studies, stellar dynamics and X-ray
observations on these scales, while significantly more centrally concentrated
models are not. There is a a conflict between gravitational lens time delays,
the local distance scale and standard CDM halo models.Comment: Submitted to ApJ. 22 pages, 7 figure
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