to the observed intrinsic scatter, the data indicate that most early-type galaxies formed their stars at high redshift with a burst of star formation prior to migrating to the red sequence. The observed $U$-$V$ color evolution with redshift is weaker than passive evolution predicts; possible mechanisms to slow the color evolution include increasing amounts of dust in quiescent galaxies towards higher redshift, red mergers at $z\!\lesssim$1, and a frosting of relatively young stars from star formation at later times.'
author:
- 'Katherine E. Whitaker, Pieter G. van Dokkum, Gabriel Brammer, Mariska Kriek, Marijn Franx, Ivo Labbé, Danilo Marchesini, Ryan F. Quadri, Rachel Bezanson, Garth D. Illingworth, Kyoung-Soo Lee, Adam Muzzin, Gregory Rudnick, David A. Wake'
bibliography:
- 'AgeSpreadref.bib'
title: 'The Age Spread of Quiescent Galaxies with the NEWFIRM Medium-band Survey: Identification of the Oldest Galaxies out to $z\!\sim$2'
---

Introduction
============

Massive galaxies with strongly suppressed star formation exist out to and beyond a redshift of $z\sim2$ [e.g. @Labbe05; @Daddi05; @Kriek06; @Kriek09; @Fontana09], and these red, quiescent galaxies form well-defined color-mass and color-magnitude relations (CMR), known as the red sequence [e.g. @Kriek08]. The scatter in the color of red sequence galaxies provides a natural marker for the variation in star 