The sizes of massive quiescent and star-forming galaxies at z ∼ 4 with ZFOURGE and CANDELS
Straatman, Caroline M. S., Labbe, Ivo, Spitler, Lee R., Glazebrook, Karl, Tomczak, Adam, Allen, Rebecca, Brammer, Gabriel B., Cowley, Michael, Dokkum, Pieter van, Kacprzak, Glenn, Kawinwanichakij, Lalit, Mehrtens, Nicola, Nanayakkara, Themiya, Papovich, Casey, Persson, S. Eric, Quadri, Ryan F., Rees, Glen, Tilvi, Vithal, Tran, Kim-Vy H., Whitaker, Katherine E.
Abstract
We study the rest-frame ultraviolet (UV) sizes of massive (~0.8 ´ 1011M☉) galaxies at 3.4 ⩽ z < 4.2, selected from the FourStar Galaxy Evolution Survey, by fitting single Sérsic profiles to Hubble Space Telescope/WFC3/ F160W images from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. Massive quiescent galaxies are very compact, with a median circularized half-light radius re = 0.63 ± 0.18 kpc. Removing 5 16 (31%) sources with signs of active galactic nucleus activity does not change the result. Star-forming galaxies have re = 2.0 ± 0.60 kpc, 3.2 ± 1.3´larger than quiescent galaxies. Quiescent galaxies at z ~ 4 are on average 6.0 ± 1.7´smaller than at z ~ 0 and 1.9 ± 0.7´smaller than at z ~ 2. Star-forming galaxies of the same stellar mass are 2.4 ± 0.7´smaller than at z ~ 0. Overall, the size evolution at 0 < z < 4 is well described by a power law, with re 5.08 0.28(1 z) = ± + -1.44±0.08 kpc for quiescent galaxies and r 6.02 0.28(1 z) e = ± + -0.72±0.05 kpc for star-forming galaxies. Compact star-forming galaxies are rare in our sample: we find only1 14 (7%) with re (M 10 M ) 1.5 11 0.75 < ☉ , whereas 13 16 (81%) of the quiescent galaxies are compact. The number density of compact quiescent galaxies at z ~ 4 is 1.8 ± 0.8 ´ 10-5 Mpc-3 and increases rapidly, by >5´, between 2 < z < 4. The paucity of compact star-forming galaxies at z ~ 4 and their large rest-frame UV median sizes suggest that the formation phase of compact cores is very short and/or highly dust obscured.