Measurement of redshift-space two- and three-point correlation of Lyα absorbers at 1.7 < z < 3.5: implications on evolution of the physical properties of IGM

Abstract

We present redshift-space two-point (ξ), three-point (ζ), and reduced three-point (Q) correlation of Lyα absorbers (Voigt profile components having H i column density, NH i > 1013.5 cm−2) over three redshift bins spanning 1.7 < z < 3.5 using high-resolution spectra of 292 quasars. We detect positive ξ up to 8 h−1 cMpc in all three redshift bins. The strongest detection of ζ = 1.81 ± 0.59 (with Q = 0.68 ± 0.23) is in $z$ = 1.7–2.3 bin at 1–2 h−1 cMpc. The measured ξ and ζ values show an increasing trend with NH i, while Q remains relatively independent of NH i. We find ξ and ζ to evolve strongly with redshift. Using simulations, we find that ξ and ζ seen in real space may be strongly amplified by peculiar velocities in redshift space. Simulations suggest that while feedback, thermal and pressure smoothing effects influence the clustering of Lyα absorbers at small scales, i.e. <0.5 h−1 cMpc, the H i photoionization rate (ΓH i) has a strong influence at all scales. The strong redshift evolution of ξ and ζ (for a fixed NH i cut-off) is driven by the redshift evolution of the relationship between NH i and baryon overdensity. Our simulation using best-fitting ΓH i($z$) 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 ΓH i 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.

Optimal 1D Ly α forest power spectrum estimation – II. KODIAQ, SQUAD, and XQ-100

“…The availability of large, high-resolution, high-S/N spectra of KODIAQ and SQUAD also kindled analysis in two-and three-point correlation functions of Ly α absorbers (Maitra, Srianand & Gaikwad 2021 ).…”

Limits on non-canonical heating and turbulence in the intergalactic medium from the low redshift Lyman α forest

“…Observationally, the redshifted Lyα transition shifts from optical to UV wavelengths at z 1.5, and can therefore only be observed from outside the atmosphere. Physically, the densities probed by the Lyα absorbers also change, from gas that is close to the mean background density, to higher density material that resides at the outskirts of galaxies (Theuns et al 1998a;Davé et al 1999Davé et al , 2010Nasir et al 2017;Maitra et al 2022). Recent progress has been largely driven by results from the Cosmic Origins Spectrograph (COS, Green et al 2012) on the Hubble Space Telescope (e.g.…”