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

Understand

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%).