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 Δη=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.