A 3% DETERMINATION OF H 0 AT INTERMEDIATE REDSHIFTS

Abstract

Recent determinations of the Hubble constant, H_0, at extremely low and very high redshifts based on the cosmic distance ladder (grounded with trigonometric parallaxes) and a cosmological model (applied to Planck 2013 data) respectively, are revealing an intriguing discrepancy (nearly 9% or 2.4sigma) that is challenging astronomers and theoretical cosmologists. In order to shed some light on this problem, here we discuss a new determination of H_0 at intermediate redshifts (z ~ 1), using the following four cosmic probes: (i) measurements of the angular diameter distances (ADD) for galaxy clusters based on the combination of Sunyaev-Zeldovich effect and X-ray data (0.14 < z < 0.89$), (ii) the inferred ages of old high redshift galaxies (OHRG) (0.62 < z < 1.70), (iii) measurements of the Hubble parameter H(z) (0.1 < z < 1.8), and (iv) the baryon acoustic oscillation (BAO) signature (z=0.35). In our analysis, assuming a flat LCDM cosmology and considering statistical plus systematic errors we obtain H_0 = 74.1^{+2.2}_{-2.2} km/s.Mpc (1sigma) which is a 3% determination of the Hubble constant at intermediate redshifts. We stress that each individual test adopted here has error bars larger than the ones appearing in the calibration of the extragalactic distance ladder. However, the remarkable complementarity among the four tests works efficiently in reducing greatly the possible degeneracy on the space parameter (Omega_m,h) ultimately providing a value of H_0 that is in excellent agreement with the determination using recessional velocities and distances to nearby objects.