The emergence of the first quiescent galaxies - take 2

Keck/MOSFIRE | 2N | PI - M. Tanaka

We propose for 2 nights of Keck/MOSFIRE observations to follow-up a z ∼ 4.7 quiescent galaxy in COSMOS as part of our on-going campaign to build a sample of distant quenched/quenching galaxies. From our previous runs (S17B- 106, S18B-040, S20B-031),(1) we have confirmed three z = 4.010, 3.99 and 3.775 galaxies, all of which are the highest redshift quiescent galaxies known to date, and (2) we have measured stellar velocity dispersions of the z = 4.010 and 3.99 galaxies, revealing that the mass in the core of these galaxies does not significantly evolve over the last 12 Gyr, which is consistent with the 2-phase formation scenario. Building upon three papers from our previous runs (Tanaka+ 2019, Valentino+ 2020, Tanaka+ in prep), we now propose to observe the most distant quenching galaxy candidate from our sample in COSMOS at z ∼ 4.7 based on the latest COSMOS2020 catalog with superb photometric quality. We aim (1) to spectroscopically confirm the emergence of the first quiescent galaxies when the Universe was only 1.2 Gyr old, and (2) to fully capture the Balmer break in the K-band to measure their star formation epoch and timescale, which will, combined with state-of-the-art simulations, give us new insights into key physics of very early quenching.