Gravitational Lens Time Delays in Cold Dark Matter

Abstract

In standard cold dark matter (CDM) halo models, the time delay of a gravitational lens is determined by the cold baryon mass fraction, fb ¼ � b; cold=� 0, of the visible galaxy relative to the overall halo. The observed time delays in PG 1115+080, SBS 1520+530, B1600+434, and HE 2149� 2745 give Hubble constants consistent with the Hubble Space Telescope Key Project value of H0 ¼ 72 � 8k m s � 1 Mpc � 1 only if fbe0:2 (onesided 68% confidence), which is larger than the upper bound of fb; max ¼ � b=� 0 ¼ 0:15 � 0:05 estimated from the cosmic microwave background. If all available baryons cool and fb ¼ fb; max, then the time delays imply H0 ¼ 65 � 6k m s � 1 Mpc � 1 (95% confidence). If local inventories of cold baryons, fb ’ 0:013=h70, are correct, then H0 ¼ 52 � 6k m s � 1 Mpc � 1 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 conflict between gravitational lens time delays, the local distance scale, and standard CDM halo models. Subject headings: cosmological parameters — dark matter — distance scale — gravitational lensing