Luminous Red Galaxies in Simulations: Cosmic Chronometers?

TL;DR

This study assesses the impact of realistic star formation histories on using Luminous Red Galaxies as cosmic chronometers to measure the universe's expansion rate, demonstrating improved accuracy with complex histories.

Contribution

It quantifies uncertainties in H(z) measurements from LRGs considering extended star formation histories and proposes optimized observational strategies.

Findings

H(z) can be recovered within 3% at z~0.42 using realistic star formation histories

Single Stellar Population fitting is insufficient for accurate galaxy age dating

Rest-frame selection criteria improve sample homogeneity

Abstract

There have been a number of attempts to measure the expansion rate of the universe at high redshift using Luminous Red Galaxies (LRGs) as "chronometers". The method generally assumes that stars in LRGs are all formed at the same time. In this paper, we quantify the uncertainties on the measurement of H(z) which arise when one considers more realistic, extended star formation histories. In selecting galaxies from the Millennium Simulation for this study, we show that using rest-frame criteria significantly improves the homogeneity of the sample and that H(z) can be recovered to within 3% at z~0.42 even when extended star formation histories are considered. We demonstrate explicitly that using Single Stellar Populations to age-date galaxies from the semi-analytical simulations provides insufficient accuracy for this experiment but accurate ages are obtainable if the complex star formation histories extracted from the simulation are used. We note, however, that problems with SSP-fitting might be overestimated since the semi-analytical models tend to over predict the late-time star-formation in LRGs. Finally, we optimize an observational program to carry out this experiment.