A Detection of $z$~2.3 Cosmic Voids from 3D Lyman-$\alpha$ Forest Tomography in the COSMOS Field

TL;DR

This paper reports the first detection of cosmic voids at redshift 2.3 using 3D Lyman-alpha forest tomography, revealing the large-scale structure of the early universe and its correspondence with galaxy distributions.

Contribution

It introduces a novel method for detecting high-redshift cosmic voids through 3D Lyman-alpha forest tomography, calibrated with hydrodynamical simulations.

Findings

Detected cosmic voids at z~2.3 in the IGM.

Void volume fraction matches simulation predictions.

Void locations are significantly underdense in galaxies.

Abstract

We present the most distant detection of cosmic voids ($z \sim 2.3$) and the first detection of three-dimensional voids in the Lyman-$\alpha$ forest. We used a 3D tomographic map of the absorption with effective comoving spatial resolution of $2.5\,h^{-1}\mathrm{Mpc}$ and volume of $3.15\times 10^5\,h^{-3}\mathrm{Mpc}^3$, which was reconstructed from moderate-resolution Keck-I/LRIS spectra of 240 background Lyman-break galaxies and quasars in a $0.16\,\mathrm{deg}^2$ footprint in the COSMOS field. Voids were detected using a spherical overdensity finder calibrated from hydrodynamical simulations of the intergalactic medium. This allows us to identify voids in the IGM corresponding to voids in the underlying matter density field, yielding a consistent volume fraction of voids in both data (19.5%) and simulations (18.2%). We fit excursion set models to the void radius function and compare the radially-averaged stacked profiles of large voids ($r > 5$ $h^{-1}$ Mpc) to stacked voids in mock observations and the simulated density field. Comparing with 432 coeval galaxies with spectroscopic redshifts in the same volume as the tomographic map, we find that the tomography-identified voids are underdense in galaxies by 5.95$\sigma$ compared to random cells.