J/ApJ/932/76ivo://CDS.VizieR/J/ApJ/932/76doi:10.26093/cds/vizier/ba-x4-2cCDSZhu Y.Becker G.D.Bosman S.E.I.Keating L.C.D'Odorico V.,Davies R.L.Christenson H.M.Banados E.Bian F.Bischetti M.Chen H.,Davies F.B.Eilers A.-C.Fan X.Gaikwad P.Greig B.Haehnelt M.G.,Kulkarni G.Lai S.Pallottini A.Qin Y.Ryan-Weber E.V.Walter F.,Wang F.Yang J.2026-07-02T11:58:40Z2025-04-16T10:10:06ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frintergalactic-mediumquasarsredshiftedvisible-astronomyspectroscopyinfrared-astronomyWe present a new investigation of the intergalactic medium near reionization using dark gaps in the Ly{beta} forest. With its lower optical depth, Ly{beta} offers a potentially more sensitive probe to any remaining neutral gas compared to the commonly used Ly{alpha} line. We identify dark gaps in the Ly{beta} forest using spectra of 42 QSOs at z_em_>5.5, including new data from the XQR-30 VLT Large Programme. Approximately 40% of these QSO spectra exhibit dark gaps longer than 10h^-1^Mpc at z~5.8. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Ly{alpha} forest are caused solely by ionizing ultraviolet background fluctuations and with models that include large neutral hydrogen patches at z<6 due to a late end to reionization. Of particular interest is a very long (L=28h^-1^Mpc) and dark ({tau}eff>~6) gap persisting down to z~5.5 in the Ly{beta} forest of the z=5.85 QSO PSO J025-11. This gap may support late reionization models with a volume-weighted average neutral hydrogen fraction of <xHI>>~5% by z=5.6. Finally, we infer constraints on <xHI> over 5.5<~z<~6.0 based on the observed Ly{beta} dark gap length distribution and a conservative relationship between gap length and neutral fraction derived from simulations. We find <xHI><=0.05, 0.17, and 0.29 at z~5.55, 5.75, and 5.95, respectively. These constraints are consistent with models where reionization ends significantly later than z=6.2022ApJ...932...76Zhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/932/76CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/ApJ/863/92 : LAE cand. at z~5.7 in the QSOJ0148+0600 field (Becker+, 2018)J/ApJ/883/163 : OI abs. search in Keck & VLT sp. of 199 QSOs (Becker+, 2019)J/ApJ/905/51 : X-SHOOTER/ALMA QSOs. I. NIR sp. (Schindler+, 2020)J/MNRAS/506/4389 : Thermal parameters of the IGM at 2<=z<=4 (Gaikwad+, 2021)J/ApJ/923/223 : VLT/X-SHOOTER & Keck/ESI spectra of z~5 QSOs (Zhu+, 2021)http://xqr30.inaf.it/ : XQR-30 homepagehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/932/76https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/932/76http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/932/76https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/932/76https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/932/76http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/932/76GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/932/76/qsos (List of targets; table added by CDS from Paper I (Zhu+ 2021, J/ApJ/923/223))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/932/76/qsos?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/932/76/qsos?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/932/76/qsos?GETtext/xml+votable180.050000true29.9915478-36.56572310.0055555555555555566/471 4279 4507 4662 5440 7326 8713 9831 10756 16554 17068 17358 17504 18088 18155 18242 18310 18751 20116 20273 21872 23304 25375 26239 26524 26650 27041 27440 27700 30036 30849 30906 33271 34762 35304 35675 36300 44463 44753 44984 48313 48715https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/932/76?format=asciiOpticalInfrareddefaultJ/ApJ/932/76/qsosList of targets; table added by CDS from Paper I (Zhu+ 2021, J/ApJ/923/223)SimbadNameSimbad column added by the CDSmeta.idcharnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintQSOQSO namemeta.id;meta.maincharprimaryzem[5.77/6.31] QSO redshiftsrc.redshiftfloatr_zemReference on zem (1)meta.ref;src.redshiftcharSourceSource of the spectrum used for dark gap statistics (2)meta.codecharInstInstrument ("ESI" or "X-Shooter")meta.id;instrcharS/N[21/152] Signal-to-noise ratiostat.snrintFileSubset number in Figure 1 file names; column added by CDSmeta.id;meta.fileintS20Display data from Schindler+ 2020, J/ApJ/905/51 if anymeta.ref.urlintnullableNgNumber of dark gaps detected for this QSOmeta.numberintnullable_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.mainJ/ApJ/932/76/fig3Observed Ly{beta} dark gaps (Data behind Figure 3)QSOQSO namemeta.id;meta.maincharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[1/195] Index of the dark gapmeta.recordintzBlue[5.44/6.02] Redshift of the dark gap's blue endsrc.redshiftfloatf_zBlue[a] Flag on zBlue (1)meta.code;src.redshiftcharzRed[5.45/6.11] Redshift of the dark gap's red endsrc.redshiftfloatf_zRed[b] Flag on zRed (1)meta.code;src.redshiftcharl_L[>=] Limit flag on Lmeta.code.errorcharL[1/39] Dark gap length in comoving Mpc/h1.475Mpcpos.distance;phys.sizeintf_L[c] Flag on L (1)meta.code;pos.distance;phys.sizecharl_TauEff[>=] Limit flag on TauEffmeta.code.errorcharTauEff[3.2/6.8] Effective opacity of the dark gapphys.absorption.coefffloate_TauEff[0.1/0.5]? Uncertainty in TauEffstat.error;phys.absorption.coefffloatnullable