J/MNRAS/522/2019 New redshift 1.6<z<4.2 of QUBRICS QSOs (Cristiani+, 2023)
Spectroscopy of QUBRICS quasar candidates 1672 new redshifts and a golden
sample for the Sandage test of the redshift drift.
Cristiani S., Porru M., Guarneri F., Calderone G., Boutsia K., Grazian A.,
Cupani G., D'Odorico V., Fontanot F., Martins C.J.A.P., Marques C.M.J.,
Maitra S., Trost A.
<Mon. Not. R. Astron. Soc. 522, 2019-2028 (2023)>
=2023MNRAS.522.2019C 2023MNRAS.522.2019C (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; QSOs ; Redshifts ; Optical ; Positional data ;
Spectroscopy
Keywords: methods: data analysis - methods: statistical -
astronomical data bases: miscellaneous - surveys - quasars: general
Abstract:
The QUBRICS (QUasars as BRIght beacons for Cosmology in the Southern
hemisphere) survey aims at constructing a sample of the brightest
quasars with z~>2.5, observable with facilities in the Southern
Hemisphere. QUBRICS makes use of the available optical and IR
wide-field surveys in the South and of Machine Learning techniques to
produce thousands of bright quasar candidates of which only a few
hundred have been confirmed with follow-up spectroscopy. Taking
advantage of the recent Gaia Data Release 3, which contains 220
million low-resolution spectra, and of a newly developed spectral
energy distribution fitting technique, designed to combine the
photometric information with the Gaia spectroscopy, it has been
possible to measure 1672 new secure redshifts of QUBRICS candidates,
with a typical uncertainty of σz = 0.02. This significant
progress of QUBRICS brings it closer to (one of) its primary goals:
providing a sample of bright quasars at redshift 2.5 < z < 5 to
perform the Sandage test of the cosmological redshift drift. A Golden
Sample of seven quasars is presented that makes it possible to carry
out this experiment in about 1500 h of observation in 25 yr, using the
ANDES spectrograph at the 39m ELT, a significant improvement with
respect to previous estimates.
Description:
QSOs as the brightest non-transient sources, can be observed at very
high redshifts and shed light on fundamental topics such as the
formation and evolution of galactic structures and massive black
holes, the Big Bang nucleosynthesis, Cosmology, reionizations, and the
variation of the fundamental constants. As cosmic lighthouses, they
provide a unique view of the Universe through the observation of
absorption features, and the brightest QSOs are coveted as precious
tools of investigation. The QUBRICS survey (Calderone et al.
2019ApJ...887..268C 2019ApJ...887..268C, Cat. J/ApJ/887/268) has been conceived with the
aim of making up for the scarcity of bright QSOs in the Southern
Hemisphere, which is due to the historical paucity of all-sky surveys
in the South, and has produced several hundreds new spectroscopically
confirmed bright QSOs. Refining the methods of selection, a continuous
effort has been dedicated in QUBRICS to the follow-up spectroscopy
testing the selection procedures, and leading to statistically
well-defined subsamples that allowed us to address the topics of the
QSO luminosity function and cosmic re-ionization. In 2022 June, the
list of candidates derived from Papers still lacking a spectroscopic
confirmation included 5469 targets. On 2022 June 13 the GaiaDR3 was
published, providing, among a wealth of data, low-resolution spectra
for about 220 million objects, selected to have a reasonable number of
Gaia observations and to be sufficiently bright to ensure good SNR.
We make use of the DR3 spectra and of QUBRICS photometric data base
combined with a SED fitting technique, to obtain secure spectroscopic
identifications and redshifts of a significant fraction of the 5469
candidates of the QUBRICS survey.
The QUBRICS data base is made of a collection of spectroscopic and
photometric data from the literature, and all spectroscopic follow-ups
carried out in the framework of the QUBRICS survey. The photometric
data base includes optical and infrared data from several public
catalogues as Optical/IR magnitudes of SkyMapper DR1 survey, GaieEDR3
G, GRP and GBP magnitudes, JHK 2MASS IR magnitudes, W1-4 AllWise
magnitudes, Optical/IR magnitudes of PanSTARRS1 DR2 and DES survey.
Gaia catalogue additionally provides parallax and proper-motion
measurements. Spectroscopic redshifts and classifications data are
collected from SDSS DR16q, Veron-Cetty catalog, 2dF, 6dF,
Ultraluminous QSOs with SMSS DR3, ELQS quasar catalog. Leading to a
QUBRICS database of 821992 objects with a secure redshift estimate and
classification (i.e see more details in section 2). These
identifications are used to train the selection algorithms (CCA, PRF,
XGB), which are then applied on unclassified sources to find QSO
candidates. Combining the lists produced by the three algorithms
leaves 5469 candidates still lacking a spectroscopic confirmation.The
publication of Gaia low-resolution spectra gave us the chance to
significantly speed up this process. We cross-matched the candidates
list to the Gaia DR3 source table, using a 0.75 arcmin matching
radius: 2635 of the 5469 candidates turned out to have a
low-resolution spectrum available from the Gaia archive. The Gaia
spectra have been processed using GaiaXPy2 where each spectrum was
calibrated and sampled on a wavelength grid, we chose a fixed step of
20 Å and discarded the regions with wavelength < 3900 and > 9600 Å,
as these are typically very noisy.
Then as explicited in section 3 and 4, we derive, for each of them,
the redshift z, comparing a robust model of the SED to their spectro +
photometric data. The procedure described has been applied to 2635
quasar candidates produced of the QUBRICS survey with a Gaia
low-resolution spectrum. For 1672 objects the procedure produces a
redshift estimate of sufficient quality (QOP=>2) to be considered
secure. They are listed in Table For 963 objects the absence of
spectral features with sufficient SNR prevented the determination of a
redshift with the requested confidence. Results are provided in
table.dat.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 74 1672 QUBRICS candidates with a new reliable
spectroscopic identification derived from Gaia
low-resolution spectra
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See also:
J/MNRAS/511/572 : High-redshift Ultraluminous QSOs with SMSS DR3
(Onken+, 2022)
J/MNRAS/482/3458 : UVES Spectral Quasar Absorption Database DR1 (Murphy+,2019)
J/ApJ/887/268 : Bright QSOs in Southern Hemisphere (QUBRICS)
(Calderone+, 2019)
J/ApJ/871/258 : ELQS in SDSS. III. The full ELQS quasar catalog
(Schindler+, 2019)
J/ApJ/829/33 : Luminous of high-z QSOs with SDSS and WISE. II (Yang+,2016)
J/ApJS/250/26 : Spectroscopic follow-up of the QUBRICS quasars
(Boutsia+, 2020)
J/ApJS/243/5 : The ELQS in the PS1 footprint (PS-ELQS) (Schindler+, 2019)
J/ApJS/166/470 : SDSS-Spitzer type I QSOs IR photometry (Richards+, 2006)
J/other/PASA/30.4 : Corrections to the VV13 Catalogue (Flesch, 2013)
VII/289 : SDSS quasar catalog, sixteenth data release (DR16Q)
(Lyke+, 2020)
VII/259 : 6dF galaxy survey final redshift release (Jones+, 2009)
VII/258 : Quasars and Active Galactic Nuclei (13th Ed.)
(Veron-Cetty+ 2010)
VII/250 : The 2dF Galaxy Redshift Survey (2dFGRS)
(2dFGRS Team, 1998-2003)
VII/233 : 2MASS All-Sky Extended Source Catalog (XSC)
(IPAC-UMass, 2003-2006)
II/359 : The VISTA Hemisphere Survey (VHS) catalog DR4.1
(McMahon+, 2013)
II/358 : SkyMapper Southern Sky Survey. DR1.1 (Wolf+, 2018)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1
(Chambers+, 2016)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- ID Identifier quasar number of Qubrics database
(qid)
10- 11 I2 h RAh Right ascension (J2000)
13- 14 I2 min RAm Right ascension (J2000)
16- 20 F5.2 s RAs Right ascension (J2000)
22 A1 --- DE- Declination sign (J2000)
23- 24 I2 deg DEd Declination (J2000)
26- 27 I2 arcmin DEm Declination (J2000)
29- 32 F4.1 arcsec DEs Declination (J2000)
34- 39 F6.3 mag imag The i apparent magnitude in AB photometric
system and uncertainties represent 68%
confidence intervals(ipsf)
41- 45 F5.3 --- z The redshift derived from low-resolution
Gaia spectra combined with photometric data
as described in section 3 (zQU_G) (1)
47- 49 A3 --- Class Object class as QSO for all sources in
this sample (Class)
51- 55 F5.3 --- zsp ? Spectroscopic redshift obtained with
follow-up spectroscopy (zspec)
57- 66 A10 "Y:M:D" ObsDate Observation date of follow-up spectroscopy
(Obs_date)
68- 74 A7 --- Inst Spectroscopic instrument used as
DOLORES 13 times, EFOSC2 3 times and
LDSS3 9 times (Instrument)
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Note (1): The redshift estimate derived from the SED fitting described in
section 3.1 is finally passed to the marz package, that matches the
Gaia low-resolution spectrum of the object with the MARZ QSO template
and produces our final estimate for the redshift. A quality operator
QOP is also assigned to each spectrum in a human-supervised way.
The QOP scale varies from a value of 1 for inconclusive spectra to 4
for great spectra, with an absolutely certain redshift.For 1672
objects the procedure produces a redshift estimate of sufficient
quality (QOP=>2) to be considered secure.
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Luc Trabelsi [CDS] 25-Jun-2026