Large-scale periodicity in the distribution of QSO absorption-line systems

The spatial-temporal distribution of absorption-line systems (ALSs) observed in QSO spectra within the cosmological redshift interval z =0.0–4.3 is investigated on the base of our updated catalog of absorption systems. We consider so-called metallic systems including basically lines of heavy elements. The sample of the data displays regular variations (with amplitudes ∼15–20%) in the z -distribution of ALSs as well as in the η -distribution, where η is a dimensionless line-of-sight comoving distance, relatively to smoother dependences. The η -distribution reveals the periodicity with period Δ η =0.036±0.002, which corresponds to a spatial characteristic scale (108±6) h −1 Mpc or (alternatively) a temporal interval (350±20) h −1 Myr for the ΛCDM cosmological model. We discuss the possibility of a spatial interpretation of the results, treating the pattern obtained as a trace of an order imprinted on the galaxy clustering in the early Universe.