Cosmic chronometers with photometry: a new path to H(z)
Raúl Jiménez, M. Moresco, Licia Verde, B. D. Wandelt
Abstract
Abstract We present a proof-of-principle determination of the Hubble parameter H ( z ) from photometric data, obtaining a determination at an effective redshift of z = 0.75 (0.65 < z < 0.85) of H (0.75) = 105.0±7.9(stat)±7.3(sys) km s -1 Mpc -1 , with 7.5% statistical and 7% systematic (10% with statistical and systematics combined in quadrature) accuracy. This is obtained in a cosmology model-independent fashion, but assuming a linear age-redshift relation in the relevant redshift range, as such, it can be used to constrain arbitrary cosmologies as long as H ( z ) can be considered slowly varying over redshift. In particular, we have applied a neural network, trained on a well-studied spectroscopic sample of 140 objects, to the COSMOS2015 survey to construct a set of 19 thousand near-passively evolving galaxies and build an age-redshift relation. The Hubble parameter is given by the derivative of the red envelope of the age-redshift relation. This is the first time the Hubble parameter is determined from photometry at ≲ 10% accuracy. Accurate H ( z ) determinations could help shed light on the Hubble tension; this study shows that photometry, with a reduction of only a factor of two in the uncertainty, could provide a new perspective on the tension.