J/ApJ/948/35 Abundances of optically thick Lyα absorbers (Saccardi+, 2023)
Evidence of first stars-enriched gas in high-redshift absorbers.
Saccardi A., Salvadori S., D'Odorico V., Cupani G., Fumagalli M.,
Berg T.A.M., Becker G.D., Ellison S., Lopez S.
<Astrophys. J., 948, 35 (2023)>
=2023ApJ...948...35S 2023ApJ...948...35S
ADC_Keywords: Abundances; QSOs; Spectra, optical; Spectra, infrared;
Spectra, ultraviolet; Redshifts
Keywords: Chemical abundances ; Quasar absorption line spectroscopy ;
Metallicity
Abstract:
The first stars were born from chemically pristine gas. They were
likely massive, and thus they rapidly exploded as supernovae,
enriching the surrounding gas with the first heavy elements. In the
Local Group, the chemical signatures of the first stellar population
were identified among low-mass, long-lived, very metal-poor
([Fe/H]<-2) stars, characterized by high abundances of carbon over
iron ([C/Fe]>+0.7): the so-called carbon-enhanced metal-poor stars.
Conversely, a similar carbon excess caused by first-star pollution was
not found in dense neutral gas traced by absorption systems at
different cosmic time. Here we present the detection of 14 very
metal-poor, optically thick absorbers at redshift z∼3-4. Among these,
3 are carbon-enhanced and reveal an overabundance with respect to Fe
of all the analyzed chemical elements (O, Mg, Al, and Si). Their
relative abundances show a distribution with respect to [Fe/H] that is
in very good agreement with those observed in nearby very metal-poor
stars. All the tests we performed support the idea that these C-rich
absorbers preserve the chemical yields of the first stars. Our new
findings suggest that the first-star signatures can survive in
optically thick but relatively diffuse absorbers, which are not
sufficiently dense to sustain star formation and hence are not
dominated by the chemical products of normal stars.
Description:
In this work, we exploited the Large Programme "Quasars and Their
Absorption Lines: A Legacy Survey of the High-redshift Universe with
(VLT)/X-shooter" (XQ-100; Lopez+ 2016A&A...594A..91L 2016A&A...594A..91L) to collect a
sample of 54 absorption systems at redshift z∼3-4 selected by the
presence of the MgII absorption doublet. Among these systems, we
identified a subsample of 37 diffuse optically thick Lyman limit
systems (LLSs) and sub-damped Lyα systems (sub-DLAs) absorbers
that we have studied in detail. We performed Voigt profile fitting of
metal absorption features and hydrogen Lyman lines in the quasar
spectra to measure column densities. To derive relative abundances of
different elements, we applied photoionization model corrections to
the measured ionic abundances.
X-shooter is characterized by three arms that allow us to cover in one
observation the full spectral range between the atmospheric cutoff at
300nm and the near-infrared K-band at 2500nm, at an intermediate
resolving power. The full spectral coverage, along with a well-defined
target selection and the high signal-to-noise ratio (S/N) achieved
(median S/N=30).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 126 30 Absorption redshift, neutral hydrogen column density,
iron abundance, and relative chemical abundances for
all absorption systems with a measure/Upper limit
of FeII
table6.dat 105 577 Voigt fit parameters
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See also:
J/AJ/103/1987 : Stars of very low metal abundance (Beers+ 1992)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/AJ/130/2804 : Carbon abundances in metal-poor stars (Rossi+, 2005)
J/A+A/501/519 : Extremely metal-poor turnoff stars abund. (Bonifacio+, 2009)
J/ApJ/724/341 : Nucleosynthesis of massive metal-free stars (Heger+, 2010)
J/ApJ/762/27 : Most metal-poor stars. III. [Fe/H]≤-3.0 stars (Yong+, 2013)
J/ApJ/797/21 : Carbon-enhanced metal-poor stars (Placco+, 2014)
J/A+A/581/A22 : 67 CEMP-s stars model analysis (Abate+, 2015)
J/A+A/579/A28 : Abundances of 3 CEMP stars (Bonifacio+, 2015)
J/MNRAS/462/3285 : XQ-100. X-shooter quasar spectra (Perrotta+, 2016)
J/MNRAS/458/4074 : UVES Advanced Data Products QSO Sample. VI. (Quiret+, 2016)
J/MNRAS/456/4488 : XQ-100 survey neutral gas (Sanchez-Ramirez+, 2016)
J/ApJ/833/20 : Carbon-enhanced metal-poor (CEMP) star abund. (Yoon+, 2016)
J/MNRAS/464/L56 : DLA properties and EW of 36 QSOs (Berg+, 2017)
J/A+A/611/A76 : DLAS dust-corrected metallicity (De Cia+, 2018)
J/ApJS/237/13 : Models and yields of massive stars (Limongi+, 2018)
J/ApJ/857/111 : Stellar yields of rot. first stars. II. (Takahashi+, 2018)
J/A+A/630/A104 : Disk and halo stars C, O and Fe abundances (Amarsi+, 2019)
J/A+A/621/A108 : RVel compilation for 45 CEMP-no stars (Arentsen+ 2019)
J/MNRAS/488/4356 : Sub-damped Lyα systems in XQ-100 survey (Berg+, 2019)
J/MNRAS/482/3458 : UVES Spectral Quasar Absorption Database DR1 (Murphy+, 2019)
J/ApJ/870/122 : Spectroscopy of low-metallicity star cand. (Placco+, 2019)
J/MNRAS/502/4009 : Sub-damped Lyman α systems in XQ-100 II (Berg+, 2021)
J/A+A/651/A79 : TO stars metallicity estimate (Bonifacio+, 2021)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name QSO name (JHHMM+DDMM) (G1)
12- 14 A3 --- f_Name Flag(s) on Name (1)
16- 22 F7.5 --- zabs [3/4.3] Absorption redshift
24- 28 F5.2 --- NHI [17.2/19.9] Neutral hydrogen column density
30- 33 F4.2 --- e_NHI [0.15/0.3] NHI uncertainty
35- 39 F5.2 [Sun] logZ [-2.91/-0.25] Metal abundance
41 A1 --- l_[Fe/H] Limit flag on [Fe/H]
43- 47 F5.2 [Sun] [Fe/H] [-3.3/0.8] Fe/H abundance
49- 52 F4.2 [Sun] e_[Fe/H] [0.1/0.3]? [Fe/H] uncertainty
54 A1 --- l_[C/H] Limit flag on [C/H]
56- 60 F5.2 [Sun] [C/H] [-2.55/2.1] C/H abundance
62- 65 F4.2 [Sun] e_[C/H] [0.13/0.2]? [C/H] uncertainty
67 A1 --- l_[O/H] Limit flag on [O/H]
69- 73 F5.2 [Sun] [O/H] [-2.5/2.2]? O/H abundance
75- 78 F4.2 [Sun] e_[O/H] [0.16/0.3]? [O/H] uncertainty
80 A1 --- l_[Mg/H] Limit flag on [Mg/H]
82- 86 F5.2 [Sun] [Mg/H] [-2.52/0.96]? Mg/H abundance
88- 91 F4.2 [Sun] e_[Mg/H] [0.14/0.3]? [Mg/H] uncertainty
93- 97 F5.2 [Sun] [Al/H] [-3.2/-0.09]? Al/H abundance
99-102 F4.2 [Sun] e_[Al/H] [0.1/0.3]? [Al/H] uncertainty
104-108 F5.2 [Sun] [Si/H] [-2.51/0.1] Si/H abundance
110-113 F4.2 [Sun] e_[Si/H] [0.12/0.3] [Si/H] uncertainty
115 A1 --- l_[C/Fe] Limit flag on [C/Fe]
117-121 F5.2 [Sun] [C/Fe] [-2.17/1.9] C/Fe abundance (2)
123-126 F4.2 [Sun] e_[C/Fe] [0.07/0.3]? [C/Fe] uncertainty
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Note (1): Flag as follows:
b = Very metal-poor absorption systems with [Fe/H]<-2
c = The carbon-enhanced very metal-poor absorbers
Note (2): [C/Fe] is computed directly by using the carbon and
iron column densities.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name System identifier (G1)
12- 18 F7.5 --- zAvg [3/4.3] Average spectroscopic redshift of system
20- 68 A49 --- Trans Transition
70- 78 F9.7 --- z [3/4.5] Central spectroscopic redshift from Trans
80 A1 --- l_logN Limit flag on logN
81- 86 F6.3 [cm-2] logN [11.1/17.5] log column density in Trans
88- 92 F5.3 [cm-2] e_logN [0/0.7]? Uncertainty in logN
94- 99 F6.3 --- b [5/66]? Doppler broadening parameter
101-105 F5.3 --- e_b [0/10]? Uncertainty in b
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Global notes:
Note (G1): ID J0124+0347 is very likely a misprint for J0121+0347 given
in the XQ-100 sample; corrected at CDS.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 25-Apr-2025