COSMOS Spectroscopic Redshift Compilation (First Data Release): 488k Redshifts Encompassing Two Decades of Spectroscopy

Abstract

We present the COSMOS Spectroscopic Redshift Compilation encompassing ~ 20 years of spectroscopic redshifts within a 10 deg${}^2$ area centered on the 2 deg${}^2$ COSMOS legacy field. This compilation contains 487,666 redshifts of 266,284 unique objects from 138 individual observing programs up to $z\sim 8$ with median stellar mass $\sim 10^{8.4}$ to $10^{10}$ M${}_{\odot }$ (redshift dependent). Rest-frame $NUVrJ$ colors and SFR -- stellar mass correlations show the compilation primarily contains low- to intermediate-mass star-forming and massive, quiescent galaxies at $z<1.25$ and mostly low-mass bursty star-forming galaxies at $z>2$. Sources in the compilation cover a diverse range of environments, including protoclusters such as ``Hyperion''. The full compilation is 50\% spectroscopically complete by $i\sim 23.4$ and $K_s\sim 21.6$ mag; however, this is redshift dependent. Spatially, the compilation is $>50$\% ($>30$\%) complete within the central (outer) region limited to $i<24$ mag and $K_s<22.5$ mag, separately. We demonstrate how the compilation can be used to validate photometric redshifts and investigate calibration metrics. By training self-organizing maps on COSMOS2020/Classic and projecting the compilation onto it, we find key galaxy subpopulations that currently lack spectroscopic coverage including $z<1$ intermediate-mass quiescent galaxies and low-/intermediate-mass bursty star-forming galaxies, $z\sim 2$ massive quiescent galaxies, and $z>3$ massive star-forming galaxies. This highlights how combining self-organizing maps with our compilation can provide guidance for future spectroscopic observations to get a complete spectroscopic view of galaxy populations. Lastly, the compilation will undergo periodic data releases that incorporate new spectroscopic redshift measurements, providing a lasting legacy resource for the community.

36 pages, 15 figures, 4 tables. Accepted for publication in ApJS. The compilation is publicly available via our github repository (https://github.com/cosmosastro/speczcompilation)