An Extremely Massive Quiescent Galaxy at z = 3.493: Evidence of Insufficiently Rapid Quenching Mechanisms in Theoretical Models*
Ben Forrest, Marianna Annunziatella, Gillian Wilson, Danilo Marchesini, Adam Muzzin, Michael C. Cooper, Z. Cemile Marsan, Ian McConachie, J. Chan, Percy Gómez, Erin Kado-Fong, F. La Barbera, Ivo Labbé, Daniel Lange-Vagle, Julie Nantais, M. Nonino, Theodore Peña, P. Saracco, Mauro Stefanon, R. F. J. van der Burg
Abstract
Abstract We 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 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 ⊙ yr −1 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.