The Assembly History of Massive Galaxies: What Do We Know?
Christopher J. Conselice

TL;DR
This paper reviews the formation and assembly history of massive galaxies, highlighting that most are established by redshift 1 with early formation of the most massive ones, and that major mergers are key in their assembly.
Contribution
It synthesizes recent observational evidence to clarify the timeline and processes, especially the role of major mergers, in the formation of massive galaxies.
Findings
Most massive galaxies are established by z~1.
Major mergers predominantly occur at z > 2.
High-mass galaxies form early and experience limited growth afterward.
Abstract
Understanding the formation history of massive galaxies is one of most popular and longstanding problems in astronomy, with observations and theory addressing how and when these systems assembled. Since the most massive galaxies in today's universe, with M_*> 10^11 M_0, are nearly all elliptical with uniform old stellar populations, we must probe higher redshifts to discover their full origins. A recent consensus has developed that nearly all M_* > 10^11 M_0 galaxies we see today were established by z~1, with at most a factor of two growth in stellar mass and number densities at lower redshifts. We review the evidence for this, and discuss how recent observations of star formation rates, colors, and morphologies of massive galaxies at z < 1 with M_* > 10^11 M_0 show that these systems are still experiencing some evolution. Massive galaxies undergo on average a single major merger at z <…
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Taxonomy
TopicsAstronomy and Astrophysical Research · Stellar, planetary, and galactic studies · Astrophysics and Star Formation Studies
