Void BAO measurements on quasars from eBOSS

We present the clustering of voids based on the quasar (QSO) sample of the extended Baryon Oscillation Spectroscopic Survey Data Release 16 in configuration space. We define voids as overlapping empty circumspheres computed by Delaunay tetrahedra spanned by quartets of quasars, allowing for an estimate of the depth of underdense regions. To maximize the baryon acoustic oscillation (BAO) signal-to-noise ratio, we consider only voids with radii larger than 36h(-1)Mpc. Our analysis shows a negative BAO peak in the cross-correlation of QSOs and voids. The joint BAO measurement of the QSO autocorrelation and the corresponding cross-correlation with voids shows an improvement in 70 per cent of the QSO mocks with an average improvement of similar to 5 percent. However, on the SDSS data, we find no improvement compatible with cosmic variance. For both mocks and data, adding voids does not introduce any bias. We find under the flat Lambda CDM assumption, a distance joint measurement on data at the effective redshift z(eff )= 1.51 of D-V(z(eff)) = 26.558 +/- 0.553. A forecast of a DESI-like survey with 1000 boxes with a similar effective volume recovers the same results as for light-cone mocks with an average of 4.8 per cent improvement in 68 per cent of the boxes.