The size-star formation relation of massive galaxies at 1.5<z<2.5

TL;DR

This study investigates the size and star formation activity relationship in massive galaxies at redshifts 1.5 to 2.5, revealing that quiescent galaxies are significantly smaller and have distinct structural properties compared to star-forming counterparts and local galaxies.

Contribution

It provides a detailed analysis of the size-star formation relation in a large, complete sample of high-redshift massive galaxies, confirming and extending previous findings with improved significance.

Findings

Quiescent galaxies are significantly smaller than star-forming ones at z~2.

A median factor of 0.34 smaller sizes for quiescent galaxies compared to local counterparts.

Quiescent galaxies' properties are incompatible with passive evolution, indicating different formation histories.

Abstract

We study the relation between size and star formation activity in a complete sample of 225 massive (M > 5 x 10^10 Msun) galaxies at 1.5<z<2.5, selected from the FIREWORKS UV-IR catalog of the CDFS. Based on stellar population synthesis model fits to the observed restframe UV-NIR SEDs, and independent MIPS 24 micron observations, 65% of galaxies are actively forming stars, while 35% are quiescent. Using sizes derived from 2D surface brightness profile fits to high resolution (FWHM_{PSF}~0.45 arcsec) groundbased ISAAC data, we confirm and improve the significance of the relation between star formation activity and compactness found in previous studies, using a large, complete mass-limited sample. At z~2, massive quiescent galaxies are significantly smaller than massive star forming galaxies, and a median factor of 0.34+/-0.02 smaller than galaxies of similar mass in the local universe. 13% of the quiescent galaxies are unresolved in the ISAAC data, corresponding to sizes <1 kpc, more than 5 times smaller than galaxies of similar mass locally. The quiescent galaxies span a Kormendy relation which, compared to the relation for local early types, is shifted to smaller sizes and brighter surface brightnesses and is incompatible with passive evolution. The progenitors of the quiescent galaxies, were likely dominated by highly concentrated, intense nuclear star bursts at z~3-4, in contrast to star forming galaxies at z~2 which are extended and dominated by distributed star formation.