Speaker
Description
Quasars are powerful tracers of the large-scale structure of the Universe at redshifts where dense galaxy samples are harder to obtain. In this work, we use the Quaia quasar catalog, considering the G<20.5 and G<20.0 magnitude-limited samples, to reconstruct and characterize the cosmic web traced by quasars. After applying a sigma-clipping selection in the $(z, z_{\mathrm{error}}/z)$ plane, we retain approximately $67.2\%$ of the $G<20.0$ sample and $61.3\%$ of the $G<20.5$ sample. We then build volume-limited samples, estimate their luminosity function and two-point correlation function using the Landy–Szalay estimator, and assign halo masses to the quasar hosts.
From this information, we reconstruct the density field with a halo-based method and extract the filamentary skeleton using DisPerSE. We analyze the dependence of the filament properties on the smoothing scale and apply a geometric filtering procedure to mitigate boundary-induced artifacts in the skeleton. The final filament catalog is characterized separately in the Galactic North and South through length distributions, vertex-separation distributions, occupation statistics, cumulative distribution functions, and filament number densities.
These measurements reveal indications of hemispheric asymmetries. We therefore perform a targeted overdensity analysis using radial filament counts, angular sweeps on the sky, quasar–filament cross-correlation measurements, and visual inspection of quasar concentrations around the reconstructed skeleton. We find consistent signatures of simultaneous overdensities in both quasars and filaments, not primarily associated with the Magellanic Clouds, suggesting the possible presence of a large-scale structure, potentially analogous to reported features such as the Hercules–Corona Borealis Great Wall or the Giant GRB Ring. This work demonstrates that quasar samples, halo-based density reconstruction, and DisPerSE skeleton extraction provide a reproducible route to mapping the cosmic web across large cosmological volumes.
| Other topic / keywords: | Cosmic web; large-scale structure; quasars; clustering; correlation function; halo-based method; density field reconstruction; DisPerSE. |
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