Ly{alpha} absorbers redshifts

Simulations suggest that while feedback, thermal and pressure smoothing effects influence the clustering of Ly{alpha} absorbers at small scales, i.e. <0.5h^-1^cMpc, the HI photoionization rate ({GAMMA}_HI_) has a strong influence at all scales. The strong redshift evolution of {xi} and {dzeta} (for a fixed N_HI_ cut-off) is driven by the redshift evolution of the relationship between _HI_ and baryon overdensity. Our simulation using best- fitting {GAMMA}_HI_(z) measurements produces consistent clustering signals with observations at z~2 but underpredicts the clustering at higher redshifts.

One possible remedy is to have higher values of {GAMMA}_HI_ at higher redshifts. Alternatively the discrepancy could be related to non-equilibrium and inhomogeneous conditions prevailing during He ii reionization not captured by our simulations.