Impact of young stellar components on quiescent galaxies: deconstructing cosmic chronometers

Understand

Cosmic chronometers may be used to measure the age difference between passively evolving galaxy populations to calculate the Hubble parameter H(z).

• The age estimator emerges from the relationship between the amplitude of the rest frame Balmer break at 4000 angstroms and the age of a galaxy, assuming that there is one single stellar population within each galaxy.
• However, recent literature has shown possible contamination (up to 2.4% of the stellar mass in a high redshift sample) of a young component embedded within the predominantly old population of the quiescent galaxy.
• We compared the data with the predictions of each model, using a new approach of distinguishing between systematic and statistical errors (in previous works, these had incorrectly been added in quadrature) and evaluating the effects of contamination by a young stellar component.