THE AGE-REDSHIFT RELATIONSHIP OF OLD PASSIVE GALAXIES

We use 32 age measurements of passively evolving galaxies as a function of redshift to test and compare the standard model (λCDM) with the R_h = ct universe. We show that the latter fits the data with a reduced χ_dof² = 0.435 for a Hubble constant = H₀ 67.2_-4.0 ^+4.5 km s^-1 Mpc^-1. By comparison, the optimal flat λCDM model, with two free parameters (including ω_m = 0.12_-0.11^+0.54 and = - H 94.3+ 0 35.8 32.7 km s?1 Mpc-1), fits the age-z data with a reduced c = 0.428 dof 2 . Based solely on their cdof 2 values, both models appear to account for the data very well, though the optimized ?CDM parameters are only marginally consistent with those of the concordance model (Wm = 0.27 and H0 = 70 km s-1 Mpc-1). Fitting the age-z data with the latter results in a reduced χ_dof² = 0.523. However, because of the different number of free parameters in these models, selection tools, such as the Akaike, Kullback and Bayes Information Criteria, favor R_h = ct over ?CDM with a likelihood of ?66.5%80.5% versus ∼19.5%33.5%. These results are suggestive, though not yet compelling, given the current limited galaxy age-z sample. We carry out Monte Carlo simulations based on these current age measurements to estimate how large the sample would have to be in order to rule out either model at a ∼99.7% confidence level. We find that if the real cosmology is λCDM, a sample of ?45 galaxy ages would be sufficient to rule out Rh = ct at this level of accuracy, while ?350 galaxy ages would be required to rule out λCDM if the real universe were instead Rh = ct. This difference in required sample size reflects the greater number of free parameters available to fit the data with λCDM.