J/A+A/705/A16 IGM metal enrichment with UVES deep spectrum (Di Stefano+, 2026)
Detecting metal enrichment of the intergalactic medium with the two-point
correlation function of the flux. Application to the UVES deep spectrum.
Di Stefano S., D'Odorico V., Cupani G., Milakovic D., Trost A.,
Crisitiani S., Viel M., Carswell R.F.
<Astron. Astrophys. 705, A16 (2026)>
=2026A&A...705A..16D 2026A&A...705A..16D (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Spectroscopy ; Redshifts ; Radio lines
Keywords: intergalactic medium - quasars: absorption lines
Abstract:
The 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
NHI>14.0 are deabsorbed), the peak is no longer significant at
1σ, even though seven weak CIV systems are still detectable by
eye. Even after including up to 135 additional weak mock CIV systems
(logNHI<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.
Description:
We analyse the ultra high S/N and high resolution UVES/VLT spectrum of
the quasar HE0940-1050 (presented in D'Odorico et al.,
2016MNRAS.463.2690D 2016MNRAS.463.2690D, and included in the SQUAD sample, Murphy et al.,
2019MNRAS.482.3458M 2019MNRAS.482.3458M, Cat. J/MNRAS/482/3458), to access the detection
of the weak IGM absorbers with the 2-point correlation function
method. We provide the Voigt fitting parameters of all CIV lines and
the associated HI lines (as obtained from D'Odorico et al.,
2016MNRAS.463.2690D 2016MNRAS.463.2690D), plus the parameters of all other metal lines
identified in the CIV forest region.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 74 234 *CIV systems and associated HI
table2.dat 62 58 *Other metal transitions
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Note on table1.dat: Parameters obtained by D'Odorico+16 from the fit of all CIV
lines. We also include the CIV mock measurements derived from the upper limits.
Note on table2.dat: Metal transitions, other than CIV, identified in the
spectrum, with the corresponding Voigt parameters.
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See also:
J/MNRAS/482/3458 : UVES Spectral Quasar Absorption Database DR1 (Murphy+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 F8.6 --- zHI ?=- Redshift of HI transition (1)
10- 17 F8.6 --- e_zHI ?=- Error on z_HI (1)
19- 24 F6.3 [cm-2] logNHI ?=- Logarithm of HI column density (1)
26- 30 F5.3 [cm-2] e_logNHI ?=- Uncertainty on logNHI (1)
32- 40 F9.7 --- zCIV ?=- Redshift of associated CIV (2)
42- 50 F9.7 --- e_zCIV ?=- Error on z_CIV (2)
52- 57 F6.3 [cm-2] logNCIV Logarithm of CIV column density (2)
59- 63 F5.3 [cm-2] e_logNCIV ?=- Uncertainty on logNCIV (2)
65- 69 F5.2 km/s b Doppler parameter CIV (2)
71- 74 F4.2 km/s e_b ?=- Uncertainty on b (2)
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Note (1): When a CIV component is associated with the same HI line as the
previous CIV component in the table, the HI parameter columns are
filled with "-".
Note (2): In case of CIV mock measurements, we indicate only logNCIV and
b=7km/s and fill the other CIV parameters with "-".
The column density of mock measurements associated with
13<logN(HI)<13.5 is computed as logN(CIV)=logN(HI)-2.5.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Trans Atomic transition
21- 29 F9.7 --- z Absorption redshift
31- 39 F9.7 --- e_z Uncertainty on z
41- 46 F6.3 [cm-2] logN Logarithm of column density
48- 52 F5.3 [cm-2] e_logN Uncertainty on logN
54- 57 F4.1 km/s b Doppler parameter
59- 62 F4.1 km/s e_b Uncertainty on b
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Acknowledgements:
Simona Di Stefano, simona.distefano(at)phd.units.it
(End) Patricia Vannier [CDS] 05-Nov-2025