$z\sim2.6$.'
author:
- 'Danilo Marchesini, Katherine E. Whitaker, Gabriel Brammer, Pieter G. van Dokkum, Ivo Labbé, Adam Muzzin, Ryan F. Quadri, Mariska Kriek, Kyoung-Soo Lee, Gregory Rudnick, Marijn Franx, Garth D. Illingworth and David Wake'
title: 'The Most Massive Galaxies at $3.0 \leq z<4.0$ in the NEWFIRM Medium-Band Survey: Properties and Improved Constraints on the Stellar Mass Function'
---

INTRODUCTION {#sec-in}
============

Understanding the formation mechanisms and evolution with cosmic time of galaxies is one of the major goals of observational cosmology. An effective approach to understand the physical processes governing the assembly of galaxies (and their relative importance as a function of cosmic time) is to directly measure the growth of the stellar mass in galaxies. Galaxies can build their stellar mass both from in-situ star formation and/or merger events. The mean space density of galaxies per unit stellar mass, or stellar mass function (SMF), is one of the most fundamental of all cosmological observables. The shape of the SMF retains the imprint of galaxy formation and evolution processes. Therefore, the SMF and its evolution with cosmic time represent a powerful tool to constrain the physical mechanisms regulating the assembly and the evolution of galaxies.

In the past decade, 