Morphologies of Two Massive Old Galaxies at z ~ 2.5

TL;DR

This study uses NICMOS imaging to reveal that two massive galaxies at z ~ 2.5 are dominated by old stellar disks, indicating early formation through dissipative collapse and potential contributions to present-day spheroid populations.

Contribution

First direct imaging evidence of massive old stellar disks at high redshift, suggesting early galaxy formation via dissipative collapse.

Findings

Both galaxies have old stellar disks with one also having a small bulge.

Presence of massive old disks at high redshift supports early dissipative collapse models.

Disks of old stars may contribute significantly to modern spheroid stellar populations.

Abstract

We present the results of NICMOS imaging of two massive galaxies photometrically selected to have old stellar populations at z ~ 2.5. Both galaxies are dominated by apparent disks of old stars, although one of them also has a small bulge comprising about 1/3 of the light at rest-frame 4800 A. The presence of massive disks of old stars at high redshift means that at least some massive galaxies in the early universe have formed directly from the dissipative collapse of a large mass of gas. The stars formed in disks like these may have made significant contributions to the stellar populations of massive spheroids at the present epoch.