Transverse and longitudinal correlation functions in the intergalactic medium from 32 close pairs of high-redshift quasars★

Abstract

We present the transverse flux correlation function of the Lyα forest in quasar absorption spectra at z∼ 2.1 from VLT-FORS and VLT-UVES observations of a total of 32 pairs of quasars; 26 pairs with separations in the range 0.6 < θ < 4 arcmin and six pairs with 4 < θ < 10 arcmin. Correlation is detected at the 3σ level up to separations of the order of ∼4 arcmin (or ∼4.4 h−1 Mpc comoving at z= 2.1 for Ωm= 0.3 and ΩΛ= 0.7). We have, furthermore, measured the longitudinal correlation function at a somewhat higher mean redshift (z= 2.39) from 20 lines of sight observed with high spectral resolution and high signal-to-noise ratio with VLT-UVES. We compare the observed transverse and longitudinal correlation functions to that obtained from numerical simulations and illustrate the effect of spectral resolution, thermal broadening and peculiar motions. The shape and correlation length of the correlation functions are in good agreement with those expected from absorption by the filamentary and sheet-like structures in the photoionized warm intergalactic medium predicted in cold dark matter (CDM)-like models for structures formation. Using a sample of 139 C iv systems detected along the lines of sight towards the pairs of quasars we also investigate the transverse correlation of metals on the same scales. The observed transverse correlation function of intervening C iv absorption systems is consistent with that of a randomly distributed population of absorbers. This is likely due to the small number of pairs with separation less than 2 arcmin. We detect, however, a significant overdensity of systems in the sightlines towards the quartet Q 0103−294A&B, Q 0102−2931 and Q 0102−293 which extends over the redshift range 1.5 ≤z≤ 2.2 and an angular scale larger than 10 arcmin.