COSMOS Spectroscopic Redshift Compilation (First Data Release): 488,000 Redshifts Encompassing Two Decades of Spectroscopy

January 2026 • 2026ApJS..282....6K

Authors • Khostovan, Ali Ahmad • Kartaltepe, Jeyhan S. • Salvato, Mara • Ilbert, Olivier • Casey, Caitlin M. • Algera, Hiddo • Antwi-Danso, Jacqueline • Battisti, Andrew • Brinch, Malte • Brusa, Marcella • Calabrò, Antonello • Capak, Peter L. • Chartab, Nima • Cooper, Olivia R. • Cox, Isa G. • Darvish, Behnam • Drakos, Nicole E. • Faisst, Andreas L. • George, Matthew R. • Gozaliasl, Ghassem • Harish, Santosh • Hasinger, Günther • Hatamnia, Hossein • Iovino, Angela • Jin, Shuowen • Kashino, Daichi • Koekemoer, Anton M. • Laishram, Ronaldo • Lee, Khee-Gan • Lertprasertpong, Jitrapon • Lilly, Simon J. • Liu, Daizhong • Masters, Daniel C. • Mobasher, Bahram • Nagao, Tohru • Onodera, Masato • Peng, Yingjie • Sanders, David B. • Sanders, Ryan L. • Sattari, Zahra • Scoville, Nick • Shah, Ekta A. • Silverman, John D. • Suzuki, Nao • Taamoli, Sina • Tanaka, Masayuki • Tasca, Lidia A. M. • Toft, Sune • Toni, Greta • Trakhtenbrot, Benny • Trump, Jonathan R. • Vaccari, Mattia • Valentino, Francesco • Vanderhoof, Brittany N. • Weaver, John R. • Yun, Min S. • Zavala, Jorge A.

Abstract • We present the COSMOS Spectroscopic Redshift Compilation encompassing ∼20 yr of spectroscopic redshifts within a 10 deg² area centered on the 2 deg² COSMOS legacy field. This compilation contains 487,666 redshifts of 266,284 unique objects from 138 individual programs up to z ∼ 8 with median stellar mass ∼10^8.4─10¹⁰ M_⊙ (redshift dependent). Rest-frame NUVrJ colors and star formation rate─stellar mass correlations show that 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 ∼ 23.4 mag and K_s ∼ 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 subpopulations currently lacking spectroscopic coverage, including z < 1 intermediate-mass quiescent and low-/intermediate-mass bursty star-forming galaxies, z ∼ 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 incorporating new spectroscopic redshifts and providing a lasting legacy resource for the community.

Links

• PREPRINT http://arxiv.org/abs/2503.00120