Size evolution of the most massive galaxies at 1.7<z<3 from GOODS NICMOS survey imaging

TL;DR

This study measures the sizes of 82 massive galaxies at redshifts 1.7 to 3, revealing their extreme compactness and comparing their sizes to present-day galaxies, providing new statistical insights into galaxy evolution.

Contribution

First large statistical analysis of massive galaxy sizes at z>2, distinguishing between disk-like and spheroid-like galaxies, and examining their size evolution and density.

Findings

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

Spheroid-like galaxies at z~2.3 are 4.3 times smaller than present-day ellipticals.

Massive galaxies at z>2 have densities similar to globular clusters, suggesting limited size evolution beyond z=3.

Abstract

We measure 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 is almost an order of magnitude larger than previous studies at these redshifts, providing the first statistical study of massive galaxy sizes at z>2, confirming the extreme compactness of these galaxies. We split our sample into disk-like (n<2) and spheroid-like (n>2) galaxies based on their Sersic indices, 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 redshifts are 4.3+/-0.7 smaller than comparatively massive elliptical galaxies today. At z>2 our results are compatible with both a leveling off, or a mild evolution in size. Furthermore, the high density (~2x10^10 M_sun kpc^-3) of massive galaxies at these redshifts, which are similar to present day globular clusters, possibly makes any further evolution in sizes beyond z=3 unlikely.