First measurement of the correlation between cosmic voids and the Lyman-$\hat{I}\pm$ forest

Abstract

We report the first detection at a median redshift $z=2.49$ of large-scale matter flows around cosmic voids. Voids are identified within a tomographic map of large-scale Lyman-$\hat{I}\pm$ (Ly$\hat{I}\pm$) transmissions, built from the eBOSS Ly$\hat{I}\pm$ forest sample in the SDSS Stripe 82 field. We measure the imprint of flows around voids, known as redshift-space distortions (RSD), with a statistical significance of $8\ddot{I}ƒ$. The observed quadrupole of the void-forest cross-correlation is described by a linear RSD model. The derived RSD parameter of the Ly$\hat{I}\pm$ forest around voids is ${\hat{I}}^2=1.21\pm 0.18$. Our model accounts for the tomographic effect induced by the Ly$\hat{I}\pm$ data being located along parallel quasar lines of sight. This work presents a novel approach to observing the growth of cosmic structures at redshifts currently inaccessible to galaxy surveys.

9 pages, 4 figures