Witnessing downsizing in the making: quiescent and breathing galaxies at the dawn of the Universe

We conduct a systematic search for \(\log(M_\ast/M_\odot) \geq 9.5\) quiescent galaxies at \(z > 3\) in six extragalactic deep fields observed with NIRCam, with the goal of extracting their physical and statistical features in a uniform and self-consistent manner. We exploit the ASTRODEEP-JWST photometric catalogs to single out robust candidates, including sources quenched only a few tens of Myr before the observation. We apply a SED-fitting procedure which explores three functional forms of star formation history and the \(\chi^2\) probabilities of the solutions, with additional checks to minimise the contamination from interlopers, tuning our selection criteria against available spectroscopic data from the DAWN archive and simulated catalogs. We select 633 candidates, which we rank by a reliability parameter based on the probabilities of the quiescent and alternative star-forming solutions, with 291 candidates tagged as “gold”. According to the best-fit models, 79% of the massive (\(\log(M_\ast/M_\odot) \geq 10.5\)) quiescent galaxies at \(3 < z < 5\) stopped forming stars at least 150 Myr before the time of observation, while 89% of low-mass sources have been quenched for less than 150 Myr. The abundance of low-mass old quiescent systems does not increase significantly with time from \(z = 5\) to 3: low-mass objects seem to be experiencing a short episode of quenching followed by rejuvenation (“breathing”), consistent with a downsizing scenario of galaxy formation. We also find an abrupt drop in the density of massive quiescent candidates at \(z > 5\). We derive estimates for the number density of early passive galaxies up to \(z = 10\) and compare them against various models: tensions with data remain in the modeling of the observed bimodality of time passed since quenching as a function of mass.