DESI Survey Validation Spectra Reveal an Increasing Fraction of Recently Quenched Galaxies at z similar to 1

We utilize similar to 17,000 bright luminous red galaxies (LRGs) from the novel Dark Energy Spectroscopic Instrument Survey Validation spectroscopic sample, leveraging its deep (similar to 2.5 hr galaxy (-1) exposure time) spectra to characterize the contribution of recently quenched galaxies to the massive galaxy population at 0.4 < z < 1.3. We use Prospector to infer nonparametric star formation histories and identify a significant population of recently quenched galaxies that have joined the quiescent population within the past similar to 1 Gyr. The highest-redshift subset (277 at z > 1) of our sample of recently quenched galaxies represents the largest spectroscopic sample of poststarburst galaxies at that epoch. At 0.4 < z < 0.8, we measure the number density of quiescent LRGs, finding that recently quenched galaxies constitute a growing fraction of the massive galaxy population with increasing look back time. Finally, we quantify the importance of this population among massive (log(M-star/M-circle dot) > 11.2) LRGs by measuring the fraction of stellar mass each galaxy formed in the gigayear before observation, f(1 Gyr). Although galaxies with f(1 Gyr) > 0.1 are rare at z similar to 0.4 (less than or similar to 0.5% of the population), by similar to 0.8, they constitute similar to 3% of massive galaxies. Relaxing this threshold, we find that galaxies with f(1 Gyr) > 5% constitute similar to 10% of the massive galaxy population at z similar to 0.8. We also identify a small but significant sample of galaxies at z = 1.1-1.3 that formed with f(1 Gyr) > 50%, implying that they may be analogs to high-redshift quiescent galaxies that formed on similar timescales. Future analysis of this unprecedented sample promises to illuminate the physical mechanisms that drive the quenching of massive galaxies after cosmic noon.