J/MNRAS/518/5590 New quasars Ca II absorbers with SDSS spectra (Fang+, 2023)
Newly discovered Ca II absorbers in the early Universe statistics, element
abundances, and dust.
Fang H., Xia I., Ge J., Willis K., Zhao Y.
<Mon. Not. R. Astron. Soc. 518, 5590-5606 (2023)>
=2023MNRAS.518.5590F 2023MNRAS.518.5590F (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Galaxies ; Spectroscopy ; Ultraviolet ; Optical ;
Equivalent widths ; Redshifts ; Positional data
Keywords: dust, extinction - galaxies: evolution - quasars: absorption lines
Abstract:
We report discoveries of 165 new quasar Ca II absorbers from the Sloan
Digital Sky Survey (SDSS) Data Releases 7 and 12. Our CA II rest-frame
equivalent width distribution supports the weak and strong
subpopulations, split at W0λ3934 = 0.7Å. Comparison of
both populations' dust depletion shows clear consistency for weak
absorber association with halo-type gas in the Milky Way (MW), while
strong absorbers have environments consistent with halo and disc- type
gas. We probed our high-redshift Ca II absorbers for 2175Å dust
bumps, discovering 122175 Å dust absorbers (2DAs). This clearly
shows that some Ca II absorbers follow the Large Magellanic Cloud
(LMC) extinction law rather than the Small Magellanic Cloud extinction
law. About 33 per cent of our strong Ca II absorbers exhibit the 2175
Å dust bump, while only 6 per cent of weak Ca II absorbers show
this bump. 2DA detection further supports the theory that strong Ca II
absorbers are associated with disc components and are dustier than the
weak population. Comparing average Ca II absorber dust depletion
patterns to that of Damped Ly α absorbers (DLAs), Mg II
absorbers, and 2DAs shows that Ca II absorbers generally have
environments with more dust than DLAs and Mg II absorbers, but less
dust than 2DAs. Comparing 2175 Å dust bump strengths from different
samples and also the MW and LMC, the bump strength appears to grow
stronger as the redshift decreases, indicating dust growth and the
global chemical enrichment of galaxies in the Universe over time.
Description:
We seek to explore the dust content of Ca II absorbers through
search for the 2175 Å dust bump. Discovery of significant dust bump
features will point towards further Ca II absorber consistency with
the LMC dust-extinction law and evaluate the effectiveness of Ca II
absorbers as a dust absorber probe. Our study's ability to access a
large sample of Ca II absorbers at high redshifts (i.e. z > 0.7)
will further increase our ability to search for the dust bump, which
has only been found at z ~> 0.7 using ground-based optical spectral
data. Further, only a limited Ca II absorber sample is currently
available because of their rarity in both number and available
studies. Thus, a greater number of absorbers, especially those in the
higher redshift range, must be discovered to support prior claims and
studies regarding their properties and environments (i.e see
Introduction).
We use quasar spectral data from SDSS-II DR7 and SDSS-III (BOSS)
DR12 for this study. We created a detection program written in python
to measure the SNR of the Ca II λλ3934, 3969 lines in
each spectrum searched and flag those with SNR => 3 and =>2.5,
respectively. Our detection program flagged about 1050 spectra for
visual inspection to distinctify between real Ca II absorbers,
questionable candidates, and false positives. The program searched for
Ca II absorption by measuring the line significance levels at the H
& K doublets. To measure line significance, W0λ3934 and
W0λ3969 were measured and their corresponding errors were
derived. From Sardane et al. (2014MNRAS.444.1747S 2014MNRAS.444.1747S, Cat.
J/MNRAS/444/1747) catalogue 303 of the Ca II absorbers were within
our Mg II absorber catalogue's redshift range of =>0.36.
The 303 of the Ca II absorbers in Sardane's catalogue were within
our Mg II absorber in redshift range of => 0.36. Of those possible
Ca II absorbers, 241 were in the Mg II absorber catalogue we
searched. The 228 of the 241 absorbers from Sardane's catalogue were
flagged by our detection program. This brings our number of new
Ca II absorber discoveries to 165 quasar Ca II absorbers (i.e see
section 2). In table2.dat, we present the 165 quasar names, redshifts
zem and zabs, astrometric positions and rest-frame equivalent
widths.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 66 165 New quasars Ca II absorbers sample discovered
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See also:
J/MNRAS/458/4074 : UVES Advanced Data Products Quasar Sample. VI.
(Quiret+, 2016)
J/MNRAS/444/1747 : CaII absorbers in SDSS QSOs (Sardane+, 2014)
J/A+A/528/A12 : QSOs CaII absorbers (Richter+, 2011)
J/ApJ/732/110 : SDSS 2175Å extinction bump candidates (Jiang+, 2011)
J/ApJ/663/320 : IR-through-UV extinction curve (Fitzpatrick+, 2007)
J/AJ/145/157 : Reddening curve of IRAS 14026+4341 (Jiang+, 2013)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
II/294 : The SDSS Photometric Catalog, Release 7
(Adelman-McCarthy+, 2009)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Index Index raw number (index)
5- 23 A19 --- Quasar Quasar name designation as JHHMMSS.ss+DDMMSS.s
(Quasar)
25- 30 F6.2 deg RAdeg Right ascension (J2000) (ra)
32- 36 F5.2 deg DEdeg Declination (J2000) (dec)
38- 41 F4.2 --- zem Redshift of the emission (zem)
43- 46 F4.2 --- zabs Redshift of the absorption (z_abs)
48- 51 F4.2 0.1nm W03934 Ca II rest-frame equivalent width at 3934Å
(W0λ3934)
53- 56 F4.2 0.1nm e_W03934 Error of W03934 (errW0λ3934)
58- 61 F4.2 0.1nm W03969 Ca II rest-frame equivalent width at 3969Å
(W0λ3969)
63- 66 F4.2 0.1nm e_W03969 Error of W03969 (errW0λ3969)
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 14-Jan-2026