Extremely Compact Massive Galaxies at 1.7<z<3

TL;DR

This study measures the sizes of 82 massive galaxies at redshifts 1.7 to 3, revealing they are significantly more compact than their present-day counterparts, with disk-like and spheroid-like galaxies being 2.6 and 4.3 times smaller respectively.

Contribution

First statistical analysis of massive galaxy sizes at z>2, distinguishing between disk-like and spheroid-like morphologies using deep HST NICMOS data.

Findings

Disk-like galaxies at z~2.3 are 2.6 times smaller than local counterparts.

Spheroid-like galaxies at the same redshift are 4.3 times smaller.

Massive galaxies at z~2.5 have stellar densities similar to globular clusters.

Abstract

We measure and analyse the sizes of 82 massive (M >= 10^11 M_Sun) galaxies at 1.7<z<3 utilizing deep HST NICMOS data taken in the GOODS North and South fields. Our sample provides the first statistical study of massive galaxy sizes at z>2. We split our sample into disk-like (Sersic index n<=2) and spheroid-like (Sersic index n>2) galaxies, and find that at a given stellar mass, disk-like galaxies at z~2.3 are a factor of 2.6+/-0.3 smaller than present day equal mass systems, and spheroid-like galaxies at the same redshift are 4.3+/-0.7 times smaller than comparatively massive elliptical galaxies today. We furthermore show that the stellar mass densities of very massive galaxies at z~2.5 are similar to present-day globular clusters with values ~2x10^10 M_Sun kpc^-3