Second Data Release of the COSMOS Lyα Mapping and Tomography Observations: The First 3D Maps of the Detailed Cosmic Web at 2.05 < z < 2.55

Abstract We present the second data release of the COSMOS Ly α Mapping And Tomography Observations Survey conducted with the Low Resolution Imaging Spectrometer on the Keck I telescope. This project used Ly α forest absorption in the spectra of faint star-forming galaxies and quasars at z ∼ 2–3 to trace neutral hydrogen in the intergalactic medium. In particular, we use 320 objects over a footprint of ∼0.2 deg 2 to reconstruct the absorption field at 2.05 < z < 2.55 at ∼2 h −1 Mpc resolution. We apply a Wiener filtering technique to the observed data to reconstruct three-dimensional (3D) maps of the field over a volume of 4.1 × 10 5 h −3 Mpc 3 . In addition to the filtered flux maps, for the first time we infer the underlying dark matter field through a forward-modeling framework from a joint likelihood of galaxy and Ly α forest data, finding clear examples of the detailed cosmic web consisting of cosmic voids, sheets, filaments, and nodes. In addition to traditional figures, we present a number of interactive 3D models to allow exploration of the data and qualitative comparisons to known galaxy surveys. We find that our inferred overdensities are consistent with those found from galaxy fields. We will make all our reduced spectra, extracted Ly α forest pixel data, and reconstructed tomographic maps publicly available upon publication.