DESI Survey Validation Spectra Reveal an Increasing Fraction of Recently Quenched Galaxies at $z\sim1$

TL;DR

This study uses deep spectroscopic data from the DESI survey to identify and analyze recently quenched massive galaxies at redshifts 0.4 to 1.3, revealing their increasing contribution to galaxy quiescence over cosmic time.

Contribution

It provides the largest spectroscopic sample of post-starburst galaxies at high redshift and quantifies the growing fraction of recently quenched galaxies among massive LRGs.

Findings

Recently quenched galaxies increase in fraction from 0.5% at z~0.4 to 10% at z~0.8.

Identified a significant sample of post-starburst galaxies at z>1.

Galaxies with high recent star formation contribute notably to the massive galaxy population.

Abstract

We utilize $\sim17000$ bright Luminous Red Galaxies (LRGs) from the novel Dark Energy Spectroscopic Instrument Survey Validation spectroscopic sample, leveraging its deep ($\sim2.5$ hour/galaxy 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 non-parametric star formation histories and identify a significant population of recently quenched galaxies that have joined the quiescent population within the past $\sim1$ Gyr. The highest redshift subset (277 at $z>1$) of our sample of recently quenched galaxies represents the largest spectroscopic sample of post-starburst 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 lookback time. Finally, we quantify the importance of this population amongst massive (\logM$>11.2$) LRGs by measuring the fraction of stellar mass each galaxy formed in the Gyr before observation, $f_\mathrm{1 Gyr}$. Although galaxies with $f_\mathrm{1 Gyr}>0.1$ are rare at $z\sim0.4$ ($\lesssim 0.5\%$ of the population), by $z\sim0.8$ they constitute $\sim3\%$ of massive galaxies. Relaxing this threshold, we find that galaxies with $f_\mathrm{1 Gyr}>5\%$ constitute $\sim10\%$ of the massive galaxy population at $z\sim0.8$. We also identify a small but significant sample of galaxies at $z=1.1-1.3$ that formed with $f_\mathrm{1 Gyr}>50\%$, implying that they may be analogues 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.