Abstract Massive quiescent galaxies have been identified out to z ∼ 7 in early JWST data, substantially exceeding (≳1 dex at z > 4) the number densities from most theoretical predictions. We investigate whether the number densities implied by the star formation histories (SFHs) of quiescent galaxies at 2 7. For this work, we rely on stellar population synthesis modeling of JWST/NIRCam photometry (from CEERS and PRIMER) and NIRSpec/PRISM spectra of massive ( M * > 10 10.5 M ⊙ ) quiescent galaxies in the RUBIES survey. We infer their SFHs through Bayesian spectrophotometric fitting with Prospector , exploring the sensitivity of our results to stellar libraries and SFH priors. For each source, we compute the timescale over which it would be identified as quiescent—leveraging the recent and most robust SFH timescale—and deduce the number densities of the quiescent population at previous epochs. These reconstructed number densities are then compared to existing observational constraints, including a new measurement from the PANORAMIC pure parallel survey, whose wide area and independent sight lines reduce sensitivity to cosmic variance. We find striking agreement between the reconstructed and observed number densities up to z ∼ 7, a self-consistency that lends credence to stellar population synthesis modeling of distant quiescent galaxies. Furthermore, by connecting the recent (∼1 Gyr) SFHs and number densities of quiescent galaxies and their implied progenitors, we reinforce the known tension between observations and model predictions at 3 < z < 7.
Zhang et al. (Tue,) studied this question.
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