The role of galaxies and AGN in reionizing the IGM - II: metal-tracing the faint sources of reionization at 5 z6
Abstract
We present a new method to study the contribution of faint sources to the UV background using the 1D correlation of metal absorbers with the intergalactic medium (IGM) transmission in a Quasi Stellar Object (QSO) sightline. We take advantage of a sample of 25 high signal-to-noise ratio QSO spectra to retrieve 150 triply-ionised carbon () absorbers at 4.5 z 6.2, of which 37 systems whose expected H~ I absorption lie in the Lyman-α forest. We derive improved constraints on the cosmic density of \,at 4.3< z < 6.2 and infer from abundance-matching that \,absorbers trace MUV -16 galaxies. Correlation with the Lyman-α forest of the QSOs indicates that these objects are surrounded by a highly opaque region at r 5 cMpc/h followed by an excess of transmission at r 10 cMpc/h detected at 2.7σ. This is in contrast to equivalent measurements at lower redshifts where only the opaque trough is detected. We interpret this excess as a statistical enhancement of the local photoionisation rate due to clustered faint galaxies around the \,absorbers. Using the analytical framework described in Paper I of this series, we derive a constraint on the average product of the escape fraction and the Lyman continuum photon production efficiency of the galaxy population clustered around the \,absorbers, fescion /[ erg-1~Hz] = 25.01+0.30-0.19. This implies that faint galaxies beyond the reach of current facilities may have harder radiation fields and/or larger escape fractions than currently detected objects at the end of the reionisation epoch.