J/A+A/710/A170 4MOST ChANGES high-redshift QSO candidates (Mkrtchyan+, 2026)
4MOST ChANGES: Catalog of high-redshift quasar candidates (4.5 < z < 7)
selected with SED fitting.
Mkrtchyan T., Mazzucchelli C., Assef R.J., Temple M.J., Rojas-Lilayu A.,
Bauer F.E., Toptun V., Acevedo Barroso J.A., Belladitta S., Farina E.P.,
Martinez-Ramirez L.N., Papini G., Satheesh-Sheeba S., Stern D.,
Upadhyayula A.
<Astron. Astrophys. 710, A170 (2026)>
=2026A&A...710A.170M 2026A&A...710A.170M (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Active gal. nuclei ; Photometry, SDSS ; Infrared ;
Redshifts
Keywords: catalogs - galaxies: active - galaxies: high-redshift -
galaxies: nuclei - quasars: photometry - quasars: general
Abstract:
The identification of high-redshift quasars (z>4.5) is critical
for studying the early Universe, supermassive-black-hole growth, and
cosmic reionization. Most known high-redshift quasars are located in
the northern hemisphere, leaving the southern sky largely unexplored.
As part of the 4-meter Multi-Object Spectroscopic Telescope (4MOST)
and Chilean AGN/Galaxy Extragalactic Survey (ChANGES) S1604 survey, we
aim to create a large catalog of high-redshift quasar candidates in
the southern hemisphere using multiwavelength photometry and
spectral-energy-distribution (SED) fitting, with the goal of
spectroscopic follow-up with 4MOST.
We constructed a multiband photometric catalog by combining optical
data from the Dark Energy Camera Local Volume Exploration Survey
(DELVE DR2) and Dark Energy Camera Legacy Survey (DECaLS DR10),
near-infrared data from the VISTA Hemisphere Survey (VHS DR5) with an
additional field of the VISTA Kilo-degree Infrared Galaxy Public
Survey (VIKING), mid-infrared data from the Wide-field Infrared Survey
Explorer (AllWISE), and optical astrometry from Gaia DR3. After
applying morphological and color-based cuts to remove contaminants
such as brown dwarfs and red galaxies, we performed a custom-made SED
fitting using quasar and brown-dwarf templates. Statistical outputs
including chi2, the Bayesian information criterion (BIC), and Ftest
were used to rank and select candidates.
Our final catalog contains 6104 high-redshift quasar candidates within
the redshift range of 4.5<z<7. These sources have
detections in seven or more photometric bands and satisfy our
SED-based statistical selection criteria (e.g., BIC>0 and Ftest>10).
Initial spectroscopic validation using the New Technology Telescope
(NTT) with the ESO Faint Object Spectrograph and Camera v.2 (EFOSC2)
and the Palomar Observatory Hale Telescope with the Next Generation
Palomar Spectrograph (NGPS) confirmed three high-redshift quasars at
z>5 out of six observed candidates.
Description:
Catalog of 6104 high-redshift quasar candidates in the southern
hemisphere (dec<5deg) within the redshift range 4.5<z<7,
selected using multiwavelength photometry and custom-made SED fitting.
The catalog combines optical data from DELVE DR2 and DECaLS DR10,
near-infrared data from VHS DR5 and VIKING, and mid-infrared data from
CatWISE 2020. Sources are required to have detections in 7 or more
photometric bands and satisfy SED-based statistical selection criteria
(BIC>0 and Ftest>10).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
catalog.dat 404 6104 Catalog of high-redshift quasar candidates
--------------------------------------------------------------------------------
See also:
II/359 : VISTA Hemisphere Survey (VHS) catalog DR4.1 (McMahon+, 2013)
II/343 : VIKING catalogue data release 2 (Edge+, 2016)
II/365 : The CatWISE2020 catalog (updated version 28-Jan-2021)
(Marocco+, 2021)
J/A+A/585/A87 : Quasar composite made from bright QSOs (Selsing+, 2016)
J/ApJ/790/54 : AGN models according to a UV to Mid-IR study (Chung+, 2014)
Byte-by-byte Description of file: catalog.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 I14 --- ObjectId Source ID from DELVE DR2 (object_id)
16- 30 F15.11 deg RAdeg Right ascension (J2000, DELVE DR2,
Drlica-Wagner et al., 2022ApJS..261...38D 2022ApJS..261...38D)
(ra)
32- 46 F15.11 deg DEdeg Declination (J2000, DELVE DR2,
Drlica-Wagner et al., 2022ApJS..261...38D 2022ApJS..261...38D)
(dec)
48- 59 F12.8 --- BDchi2min Minimum chi2 for best-fit brown dwarf
template (BDchi2min)
61- 63 A3 --- BDchi2 Best-fit brown dwarf template type template
(MD1, MD2, MD3, BD1, BD2, BD3) (BDchi2)
65- 75 F11.8 --- QSOchi2min Minimum chi2 for best-fit QSO template
(QSOchi2min)
77- 80 F4.2 --- zQSO Photometric redshift from best-fit QSO
template (QSO_z)
82- 91 F10.8 --- Rchi2 Ratio of QSO to BD chi2;
values <1 indicate better QSO fit (R_chi2)
93-106 F14.8 --- Ftestvalue F-test statistic value; >10 required for
selection (Ftestvalue)
108-117 F10.6 --- BICvalue Bayesian Information Criterion;
>0 required for selection (BIC_value)
119-122 F4.2 mag E(B-V)QSO E(B-V) dust reddening of best-fit QSO
template (QSO_EBV)
124-132 F9.6 --- EMlineQSO Emission line strength of best-fit QSO
template (-2, 0, 2) (QSO_EMline)
134 I1 --- NPoints Number of photometric bands used in
SED fitting (Data_Points)
136 I1 --- QSOPar Number of free parameters of best-fit
QSO template (QSO_Par)
138 I1 --- Prior [1/2] Source priority tier (1=higher,
2=lower confidence) (Prioritization) (1)
140-141 I2 mag gmagDEL ?=99 AB Kron g-band magnitude (DELVE DR2)
(maggdelve)
143-144 I2 mag e_gmagDEL ?=99 Uncertainty on maggdelve
(magerrgdelve)
146-154 F9.6 mag imagDEL ?=99 AB Kron i-band magnitude (DELVE DR2)
(magidelve)
156-164 F9.6 mag e_imagDEL ?=99 Uncertainty on magidelve
(magerridelve)
166-174 F9.6 mag rmagDEL ?=99 AB Kron r-band magnitude (DELVE DR2)
(magrdelve)
176-184 F9.6 mag e_rmagDEL ?=99 Uncertainty on magrdelve
(magerrrdelve)
186-194 F9.6 mag zmagDEL ?=99 AB Kron z-band magnitude (DELVE DR2)
(magzdelve)
196-203 F8.6 mag e_zmagDEL ?=99 Uncertainty on magzdelve
(magerrzdelve)
205-210 F6.3 mag W1mag ?=- WISE W1 (3.4 micron) magnitude
(CatWISE 2020); AB system (w1mpro)
212-216 F5.3 mag e_W1mag ?=- Uncertainty on w1mpro (w1sigmpro)
218-223 F6.3 mag W2mag ?=- WISE W2 (4.6 micron) magnitude
(CatWISE 2020); AB system (w2mpro)
225-229 F5.3 mag e_W2mag ?=- Uncertainty on w2mpro (w2sigmpro)
231-239 F9.6 mag YmagV ?=- VHS/VIKING Y-band Petrosian magnitude;
AB system (ypetromag)
241-249 F9.6 mag e_YmagV ?=- Uncertainty on ypetromag (ypetromagerr)
251-259 F9.6 mag JmagV ?=- VHS/VIKING J-band Petrosian magnitude;
AB system (jpetromag)
261-269 F9.6 mag e_JmagV ?=- Uncertainty on jpetromag (jpetromagerr)
271-279 F9.6 mag HmagV ?=- VHS/VIKING H-band Petrosian magnitude;
AB system (hpetromag)
281-289 F9.6 mag e_HmagV ?=- Uncertainty on hpetromag (hpetromagerr)
291-299 F9.6 mag KsmagV ?=- VHS/VIKING Ks-band Petrosian magnitude;
AB system (kspetromag)
301-309 F9.6 mag e_KsmagV ?=- Uncertainty on kspetromag (kspetromagerr)
311-319 F9.6 mag gmagDEC ?=- AB Kron g-band magnitude (DECaLS DR10,
Dey et al., 2019AJ....157..168D 2019AJ....157..168D)
(maggdecals)
321-330 F10.6 --- snrgDEC ?=- Signal-to-noise ratio for maggdecals
(snrgdecals)
332-340 F9.6 mag rmagDEC ?=- AB Kron r-band magnitude (DECaLS DR10,
Dey et al., 2019AJ....157..168D 2019AJ....157..168D)
(magrdecals)
342-351 F10.6 --- snrrDEC ?=- Signal-to-noise ratio for magrdecals
(snrrdecals)
353-361 F9.6 mag imagDEC ?=- AB Kron i-band magnitude (DECaLS DR10,
Dey et al., 2019AJ....157..168D 2019AJ....157..168D)
(magidecals)
363-372 F10.6 --- snriDEC ?=- Signal-to-noise ratio for magidecals
(snridecals)
374-382 F9.6 mag zmagDEC ?=- AB Kron z-band magnitude (DECaLS DR10,
Dey et al., 2019AJ....157..168D 2019AJ....157..168D)
(magzdecals)
384-393 F10.6 --- snrzDEC ?=- Signal-to-noise ratio for magzdecals
(snrzdecals)
395-404 F10.8 mag E(B-V) Galactic dust reddening E(B-V) from SFD maps
(Schlegel et al., 1998ApJ...500..525S 1998ApJ...500..525S) (ebv)
--------------------------------------------------------------------------------
Note (1): Prioritization=1 sources satisfy: z_delve≤22, chi2_QSO≤1.2,
and R_chi2≤0.3. Prioritization=2 sources satisfy z_delve≤22.
--------------------------------------------------------------------------------
Acknowledgements:
Tatavixk Mkrtchyan, tatevik.mkrtchyan(at)mail.udp.cl
References:
Drlica-Wagner et al., 2022ApJS..261...38D 2022ApJS..261...38D (DELVE DR2)
Dey et al., 2019AJ....157..168D 2019AJ....157..168D (DECaLS DR10)
McMahon et al., 2013Msngr.154...35M 2013Msngr.154...35M (VHS DR5) Cat. II/359
Edge et al., 2013Msngr.154...32E 2013Msngr.154...32E (VIKING) Cat. II/343
Marocco et al., 2021ApJS..253....8M 2021ApJS..253....8M (CatWISE 2020) Cat. II/365
Schlegel et al., 1998ApJ...500..525S 1998ApJ...500..525S (SFD dust maps)
Selsing et al., 2016A&A...585A..87S 2016A&A...585A..87S (QSO templates) Cat. J/A+A/585/A87
Temple et al., 2021MNRAS.508..737T 2021MNRAS.508..737T (QSO templates)
Chung et al., 2014ApJ...790...54C 2014ApJ...790...54C (BD templates) Cat. J/ApJ/790/54
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 15-Apr-2026