The existence of an old quasar at z=3.91 and its implications for Lambda(t) deflationary cosmologies

摘要

We investigate some observational constraints on decaying vacuum cosmologies based on the recently discovered old high redshift quasar APM 08279+5255. This object is located at z = 3.91 and has an estimated age of 2-3 Cyr. The class of Lambda(t) cosmologies is characterized by a positive beta parameter smaller than unity which quantifies the ratio between the vacuum and the total energy density. Assuming the lower limit age (2 Gyr) and that the cold dark matter contributes with Omega(M) = 0.2 we show that beta is constrained to be greater than or equal to 0.07 while for an age of 3 Cyr and Omega(M) = 0.4 the beta parameter must be greater than 0.32. Our analysis includes closed, flat and hyperbolic scenarios, and it strongly suggests that there is no age crisis for this kind of A(t) cosmologies. Lower limits to the redshift quasar formation are also briefly discussed to the flat case. For Omega(M) = 0.4 we found that the redshift formation is constrained by z(f) greater than or equal to 8.0.