J/A+A/705/A16ivo://CDS.VizieR/J/A+A/705/A16CDSDi Stefano S.D'Odorico V.Cupani G.Milakovic D.Trost A.,Crisitiani S.Viel M.Carswell R.F.2026-03-02T06:25:50Z2025-12-24T13:35:33ZCDS support team

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

cds-question@unistra.frquasarsspectroscopyredshiftedradio-astronomyThe distribution and the abundance of metals in the intergalactic medium (IGM) have strong implications for galaxy formation and evolution models. The ionic transitions of heavy elements in quasar spectra can be used to probe both the mechanisms and the sources of chemical pollution. However, the need for high-resolution and high signal-to-noise ratio (S/N) spectra makes it challenging to characterize the process of IGM metal enrichment since the IGM absorbers are too weak for direct detection. The aim of this work is to investigate the IGM metallicity, focusing on the detection of the weak absorption lines. We exploited the cosmological tool of the two-point correlation function (TPCF) and applied it to the transmitted flux in the CIV forest region of the ultra-high S/N UVES spectrum of the quasar HE0940-1050 (z~3). We also "deabsorbed" the strongest circum-galactic medium (CGM) systems in order to reveal the underlying IGM signal. For each of our tests, we created a catalogue of 1000 mock spectra in which we shuffled the position of the absorption lines to derive an estimate for the TPCF noise level. The TPCF shows a clear peak at the characteristic velocity separation of the CIV doublet. However, when the CGM contribution is removed (i.e. when all metal lines and CIV lines associated with log N_HI_>14.0 are deabsorbed), the peak is no longer significant at 1{sigma}, even though seven weak CIV systems are still detectable by eye. Even after including up to 135 additional weak mock CIV systems (logN_HI_<14.0) in the spectrum, we are not able to detect a significant CIV peak. Eventually, when we create a synthetic spectrum with gaussian distributed noise and the same S/N as the complete spectrum, we remove the signal caused by the spectral intrinsic features and thus find a peak compatible with a metallicity of -3.80<[C/H]<-3.50. We conclude that the TPCF method is not sensitive to the presence of the weakest systems in the real spectrum, despite the extremely high S/N and high resolution of the data. However, the results of this statistical technique could change when combining more than one line of sight.2026A&A...705A..16Dhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/705/A16CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/MNRAS/482/3458 : UVES Spectral Quasar Absorption Database DR1 (Murphy+, 2019)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/705/A16https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/705/A16http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/705/A16https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/705/A16https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/705/A16http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/705/A16GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapRadiodefaultJ/A+A/705/A16/table1*CIV systems and associated HIrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintzHI? Redshift of HI transition (1)src.redshift;pos.heliocentricdoublenullablee_zHI? Error on z_HI (1)stat.errordoublenullablelogNHI? Logarithm of HI column density (1)log(cm**-2)phys.columnDensityfloatnullablee_logNHI? Uncertainty on logNHI (1)log(cm**-2)stat.errorfloatnullablezCIV? Redshift of associated CIV (2)src.redshift;pos.heliocentricdoublenullablee_zCIV? Error on z_CIV (2)stat.errordoublenullablelogNCIVLogarithm of CIV column density (2)log(cm**-2)phys.columnDensityfloate_logNCIV? Uncertainty on logNCIV (2)log(cm**-2)stat.errorfloatnullablebDoppler parameter CIV (2)km/sspect.dopplerParamfloate_b? Uncertainty on b (2)km/sstat.errorfloatnullableJ/A+A/705/A16/table2*Other metal transitionsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTransAtomic transitionphys.atmol.transProb;phys.atmol.transitioncharzAbsorption redshiftsrc.redshiftdoublee_zUncertainty on zstat.error;src.redshiftdoublelogNLogarithm of column densitylog(cm**-2)phys.columnDensityfloate_logNUncertainty on logNlog(cm**-2)stat.errorfloatbDoppler parameterkm/sspect.dopplerParamfloate_bUncertainty on bkm/sstat.errorfloat