The sizes of massive quiescent and star forming galaxies at z~4 with ZFOURGE and CANDELS

Understand

We study the rest-frame ultra-violet sizes of massive (~0.8 x 10^11 M_Sun) galaxies at 3.4<z<4.2, selected from the FourStar Galaxy Evolution Survey (ZFOURGE), by fitting single Sersic profiles to HST/WFC3/F160W images from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS).

• Massive quiescent galaxies are very compact, with a median circularized half-light radius r_e = 0.63 +/- 0.18 kpc.
• Removing 5/16 (31%) sources with signs of AGN activity does not change the result.
• Star-forming galaxies have r_e = 2.0 +/- 0.60 kpc, 3.2 +/- 1.3 x larger than quiescent galaxies.