J/A+A/706/A273 Ly-α correlation with 67 QSOs at 5<z<6.1 (Spina+, 2026)
Measuring the intergalactic medium correlation length at 5<z<6.1:
A fast change at the end of reionization.
Spina B., Bosman S.E.I., Maity B., Davies F.B.
<Astron. Astrophys. 706, A273 (2026)>
=2026A&A...706A.273S 2026A&A...706A.273S (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Spectroscopy ; Optical ; Infrared ; Ultraviolet
Keywords: intergalactic medium - quasars: general - cosmology: observations -
dark ages - reionization - first stars
Abstract:
The Lyman-α forest of high redshift quasars is a powerful probe
of the late stages of the Epoch of Reionization (EoR), in particular
thanks to the presence of Gunn-Peterson troughs. These troughs exhibit
a broad range of lengths, with some extending up to ∼100cMpc,
suggesting large-scale coherent structures in the intergalactic medium
(IGM).
We aim to gain more insight into the presence, extent, and magnitude
of correlations in the Lyman-α forest during the end of
reionization, at 5<z<6.1. In particular, we want to quantify the
scales over which correlations are significant in order to help inform
the required size of cosmological simulations aiming to capture the
evolution of the EoR.
We utilize the extended XQR-30 dataset over the redshift range 5<z<6.1
(Δz=0.05) to explore large-scale correlations. After
accounting for the relevant systematics, the flux correlation matrix
proves to be a powerful tool for probing large-scale correlations
across redshifts. We perform an MCMC analysis to quantify the extent
and strength of the correlation, making use of several functional
forms. We moreover employ new large-volume (1.53Gpc3) light-cones
of Lyman-α transmission implementing different reionization
scenarios to interpret the observed signal, including a fiducial box
employing SCRIPT.
We detect strong correlations at redshifts z>5.3, extending at least
tens of Mpc and strongly increasing with redshift. Our results suggest
a redshift-dependent correlation length, from L≤26.53(68.47)Mpc
at 1-σ (2-σ) limit at redshift z=5.0 to
L=252.72+272.61-41.61Mpc at redshift z=6.1. On the contrary,
our simulations all demonstrate characteristic correlation scales
<60Mpc with a very slow redshift evolution, in strong tension with our
observations.
The presence and redshift-dependence of correlations in the
Lyman-α forest on >200Mpc scales at z=6 indicates that
cosmological simulations should be larger than this scale to
adequately sample the Lyman-α forest. Despite implementing a
fluctuating UVB and numerous neutral islands at z<6, and matching
well the sightline scatter in the Lyman-α forest, our fiducial
SCRIPT- based simulation fails to reproduce the large-scale
correlations. It may be that those ingredients are necessary, but not
sufficient, to understanding the unfolding of the EoR.
Description:
We use 67 QSO spectra at redshift z>5.5, with signal-to-noise ratios
SNR=>10 per≤15m/s spectral pixel. We combine observations from
the X-Shooter and ESI instruments in order to increase our sample size
and improve the statistical analysis.For each sightline, the flux is
binned into redshift bins of Δz=0.05 in the redshift range
4.97≤z≤6.125 (the redshift bins are therefore centered at
zbin=5.00,5.05,...,6.10), covering the last stage of the EoR and
entering the post-EoR regime. We have computed the flux correlation of
67 quasars sightlines to trace the end of the Epoch or Reionization.
Such sightlines are extracted from the high-resolution high-quality
E-XQR-30 observational dataset and complemented with observations from
the ESI instrument.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 92 221 *Correlation matrix and error associated for
each pair of redshift bins
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Note on table.dat: As mentioned in methods section, we aim to investigate and
quantify the strength and extent of Lyman-α forest correlations on
different scales. We achieve this by measuring the correlation between
combinations of redshift bins and evaluating its statistical significance,
accounting for systematics such as continuum reconstruction and observational
uncertainties.
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See also:
J/ApJ/863/92 : LAE cand. at z∼5.7 in the field of QSO J0148+0600
(Becker+, 2018)
J/MNRAS/506/4389 : Thermal parameters of the IGM at 2 ≤ z ≤ 4 (Gaikwad+,2021)
Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 20 F20.18 --- zbin1 First redshift bin (z1)
22- 41 F20.18 --- zbin2 Second redshift bin (z2)
43- 67 E25.19 --- Cor Correlation coefficient (F)
69- 92 E24.19 --- e_Cor Error associated to Cor (σF)
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Acknowledgements:
Benedetta Spina, spina(at)thphys.uni-heidelberg.de
(End) Benedetta Spina [Heidelberg Univ.], Luc Trabelsi [CDS] 10-Dec-2025