Exploring the z=3-4 massive galaxy population with ZFOURGE: the prevalence of dusty and quiescent galaxies

摘要

Our understanding of the redshift $z>3$ galaxy population relies largely onsamples selected using the popular "dropout" technique, typically consisting ofUV-bright galaxies with blue colors and prominent Lyman breaks. As it iscurrently unknown if these galaxies are representative of the massive galaxypopulation, we here use the FourStar Galaxy Evolution (ZFOURGE) Survey tocreate a stellar mass-limited sample at $z=3-4$. Uniquely, ZFOURGE uses deepnear-infrared medium-bandwidth filters to derive accurate photometric redshiftsand stellar population properties. The mass-complete sample consists of 57galaxies with log M $>10.6$, reaching below $M^{\star}$ at $z=3-4$. On average, the massive $z=3-4$ galaxies are extremely faint in the observedoptical with median $R_{tot}^{AB}=27.48\pm0.41$ (restframe$M_{1700}=-18.05\pm0.37$). They lie far below the UV luminosity-stellar massrelation for Lyman break galaxies and are about $\sim100\times$ fainter at thesame mass. The massive galaxies are red ($R-Ks_{AB}=3.9\pm0.2$; restframeUV-slope $\beta=-0.2\pm0.3$) likely from dust or old stellar ages. We classifythe galaxy SEDs by their restframe $U-V$ and $V-J$ colors and find a diversepopulation: $46^{+6+10}_{-6-17}$% of the massive galaxies are quiescent,$54^{+8+17}_{-8-10}$% are dusty star-forming galaxies, and only$14^{+3+10}_{-3-4}$% resemble luminous blue star forming Lyman break galaxies.This study clearly demonstrates an inherent diversity among massive galaxies athigher redshift than previously known. Furthermore,we uncover a reservoir ofdusty star-forming galaxies with $4\times$ lower specific star-formation ratescompared to submillimeter-selected starbursts at $z>3$. With $5\times$ highernumbers, the dusty galaxies may represent a more typical mode of star formationcompared to submillimeter-bright starbursts.