The Fraction of Quiescent Massive Galaxies in the Early Universe

TL;DR

This study compiles a mass-selected sample of quiescent galaxies from z~0.4 to z~4, revealing a significant fraction of such galaxies in the early universe, challenging current theoretical models.

Contribution

It provides the first comprehensive observational measurement of quiescent galaxy fractions at high redshift, enabling comparison with and testing of theoretical predictions.

Findings

Approximately 15-20% of massive galaxies are quiescent up to z~4.

A tail of 'Red&Dead' galaxies with extremely low SFR/M_* exists at high redshift.

Current models poorly match the observed fraction of quiescent galaxies.

Abstract

Aims: The aim of this work is to collect a complete, mass--selected sample of galaxies with very low specific star formation rate, for a comparison with the prediction of recent theoretical models. Method: We use the 24/K flux ratio, complemented by the SED fitting to the full 0.35-8.0 mum spectral distribution, to select quiescent galaxies from z~0.4 to z~4 in the GOODS--MUSIC sample. Our observational selection can be translated into thresholds on the specific star formation rate SFR/M_*, that can be used to compare with the theoretical predictions. Results: We find that, in the framework of the well known global decline of the quiescent fraction with redshift, a non-negligible fraction ~15-20% of massive galaxies with very low specific star formation rate exists up to z~4, including a tail of "Red&Dead" galaxies with SFR/M_*<10^{-11}/yr. Recent theoretical models vary to a large extent in the prediction of the fraction of galaxies with very low specific star formation rates, and are unable to provide a global match to our data.