Forrest, BenBenForrestAnnunziatella, MariannaMariannaAnnunziatellaWilson, GillianGillianWilsonMarchesini, DaniloDaniloMarchesiniMuzzin, AdamAdamMuzzinCooper, M. C.M. C.CooperMarsan, Z. CemileZ. CemileMarsanMcConachie, IanIanMcConachieChan, Jeffrey C. C.Jeffrey C. C.ChanGomez, PercyPercyGomezKado-Fong, ErinErinKado-FongL Barbera, FrancescoFrancescoL BarberaLabbé, IvoIvoLabbéLange-Vagle, DanielDanielLange-VagleNantais, JulieJulieNantaisNONINO, MarioMarioNONINOPeña, TheodoreTheodorePeñaSARACCO, PaoloPaoloSARACCOStefanon, MauroMauroStefanonvan der Burg, Remco F. J.Remco F. J.van der Burg2025-03-122025-03-1220202041-8205http://hdl.handle.net/20.500.12386/36694We present spectra of the most massive quiescent galaxy yet spectroscopically confirmed at z > 3, verified via the detection of Balmer absorption features in the H- and K-bands of Keck/MOSFIRE. The spectra confirm a galaxy with no significant ongoing star formation, consistent with the lack of rest-frame UV flux and overall photometric spectral energy distribution. With a stellar mass of ${3.1}_{-0.2}^{+0.1}\times {10}^{11}\,{M}_{\odot }$ at z = 3.493, this galaxy is nearly three times more massive than the highest redshift spectroscopically confirmed absorption-line-identified galaxy known. The star formation history of this quiescent galaxy implies that it formed >1000 M<SUB>⊙</SUB> yr<SUP>-1</SUP> for almost 0.5 Gyr beginning at z ∼ 7.2, strongly suggestive that it is the descendant of massive dusty star-forming galaxies at 5 < z < 7 recently observed with ALMA. While galaxies with similarly extreme stellar masses are reproduced in some simulations at early times, such a lack of ongoing star formation is not seen there. This suggests the need for a quenching process that either starts earlier or is more rapid than that currently prescribed, challenging our current understanding of how ultra-massive galaxies form and evolve in the early universe.STAMPAenArticle10.3847/2041-8213/ab5b9f2-s2.0-85081346357https://api.elsevier.com/content/abstract/scopus_id/85081346357https://iopscience.iop.org/article/10.3847/2041-8213/ab5b9f2020ApJ...890L...1FFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation