First Data Release of the COSMOS Lyman-Alpha Mapping And Tomography Observations: 3D Lyman-$\alpha$ Forest Tomography at 2.05 < z < 2.55

TL;DR

This paper presents the first data release of a 3D tomographic map of the Lyman-alpha forest at redshifts 2.05 to 2.55, reconstructed from galaxy and quasar spectra in the COSMOS field, revealing large-scale structures and protoclusters.

Contribution

It introduces a novel high-density 3D Lyman-alpha forest tomography map using faint galaxies as background sources, enabling detailed cosmic structure analysis at these redshifts.

Findings

Reconstructed a 3D Lyman-alpha absorption map over 3.15×10^5 Mpc^3 volume.

Identified large overdensities consistent with galaxy protoclusters.

Demonstrated visualization of the map in VR and interactive formats.

Abstract

Faint star-forming galaxies at $z\sim 2-3$ can be used as alternative background sources to probe the Lyman-$\alpha$ forest in addition to quasars, yielding high sightline densities that enable 3D tomographic reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Lyman-Alpha Mapping And Mapping Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck-I telescope. Over an observational footprint of 0.157$\mathrm{deg}^2$ within the COSMOS field, we used 240 galaxies and quasars at $2.17<z<3.00$, with a mean comoving transverse separation of $2.37\,h^{-1}\,\mathrm{Mpc^3}$, as background sources probing the foreground Lyman-$\alpha$ forest absorption at $2.05<z<2.55$. The Lyman-$\alpha$ forest data was then used to create a Wiener-filtered tomographic reconstruction over a comoving volume of $3.15\,\times 10^5\,h^{-3}\,\mathrm{Mpc^3}$ with an effective smoothing scale of $2.5\,h^{-1}\,\mathrm{Mpc}$. In addition to traditional figures, this map is also presented as a virtual-reality YouTube360 video visualization and manipulable interactive figure. We see large overdensities and underdensities that visually agree with the distribution of coeval galaxies from spectroscopic redshift surveys in the same field, including overdensities associated with several recently-discovered galaxy protoclusters in the volume. This data release includes the redshift catalog, reduced spectra, extracted Lyman-$\alpha$ forest pixel data, and tomographic map of the absorption.