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Belli, Sirio; Genzel, Reinhard; Förster Schreiber, Natascha M.; Wisnioski, Emily; Wilman, David J.; Wuyts, Stijn; Mendel, J. Trevor; Beifiori, Alessandra; Bender, Ralf; Brammer, Gabriel B.; Burkert, Andreas; Chan, Jeffrey; Davies, Rebecca L.; Davies, Ric; Fabricius, Maximilian; Fossati, Matteo; Galametz, Audrey; Lang, Philipp; Lutz, Dieter; Momcheva, Ivelina G.; Nelson, Erica J.; Saglia, Roberto P.; Tacconi, Linda J.; Tadaki, Ken-ichi; Übler, Hannah; Dokkum, Pieter van (2017): KMOS3D Reveals Low-level Star Formation Activity in Massive Quiescent Galaxies at 0.7 < z < 2.7. In: Astrophysical Journal Letters, Vol. 841, No. 1, L6
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Abstract

We explore the Ha emission in the massive quiescent galaxies observed by the KMOS3D survey at 0.7 < z < 2.7. The H alpha line is robustly detected in 20 out of 120 UVJ-selected quiescent galaxies, and we classify the emission mechanism using the H alpha line width and the [N II]/H alpha line ratio. We find that AGNs are likely to be responsible for the line emission in more than half of the cases. We also find robust evidence for star formation activity in nine quiescent galaxies, which we explore in detail. The Ha kinematics reveal rotating disks in five of the nine galaxies. The dust-corrected Ha star formation rates are low (0.2-7 M-circle dot yr(-1)), and place these systems significantly below the main sequence. The 24 mu m-based, infrared luminosities, instead, overestimate the star formation rates. These galaxies present a lower gas-phase metallicity compared to star-forming objects with similar stellar mass, and many of them have close companions. We therefore conclude that the low-level star formation activity in these nine quiescent galaxies is likely to be fueled by inflowing gas or minor mergers, and could be a sign of rejuvenation events.