Impact of a locally measured H_0 on the interpretation of cosmic chronometer data

Understand

Whereas many measurements in cosmology depend on the use of integrated distances or time, galaxies evolving passively on a time scale much longer than their age difference allow us to determine the expansion rate H(z) solely as a function of the redshift-time derivative dz/dt.

• These model-independent `cosmic chronometers' can therefore be powerful discriminators for testing different cosmologies.
• In previous applications, the available sources strongly disfavoured models (such as LambdaCDM) predicting a variable acceleration, preferring instead a steady expansion rate over the redshift range 0 < z < 2.
• A more recent catalog of 30 objects appears to suggest non-steady expansion.