J/ApJS/282/28 Changing-Look AGN from DESI. V. (Chen+, 2026)
Changing-Look Active Galactic Nuclei from the Dark Energy Spectroscopic
Instrument.
V. Dramatic variability in high-ionization broad emission lines.
Chen Z.-Q., Jin J.-J., Guo W.-J., Sun S.-X., Pan Z.-W., Liu C.-X.,
Cheng H.-Q., Hu J.-W., Sheng Z.-F., Zou Hu, Chen Z.-B., Zheng Qi,
Yuan Q.-R.
<Astrophys. J. Suppl. Ser., 282, 28 (2026)>
=2026ApJS..282...28C 2026ApJS..282...28C
ADC_Keywords: Active gal. nuclei; Spectra, optical; Equivalent widths;
Redshifts; QSOs; Black holes; Radio sources
Keywords: Accretion ; Supermassive black holes
Abstract:
We present a systematic search for changing-look (CL) quasars at high
redshift z>0.9 by crossmatching the spectroscopic data sets from the
Dark Energy Spectroscopic Instrument Data Release 1 and Sloan Digital
Sky Survey Data Release 18. We identify 97 CL quasars showing
significant variability in high-ionization broad emission lines,
including 45 turn-on and 52 turn-off events, corresponding to a
detection rate of ∼0.042%. The low rate relative to low-ionization CL
quasar searches is likely due to selection and physical effects in
high-ionization lines. Based on the CL quasar sample, we find that CL
quasars generally exhibit lower accretion rates compared to typical
quasars, with average Eddington ratios of logλEdd~-1.14 in
the bright state and ~-1.39 in the dim state, compared to ~-0.65 for
typical quasars. Furthermore, while high-ionization lines in CL
quasars follow the Baldwin effect on a population level, some sources
can display inverse Baldwin trends. In addition, we find a positive
correlation between the variability in high-ionization lines (e.g.,
MgII, CIII]) and the change in bolometric luminosity. We also estimate
a characteristic rest-frame timescale of ∼3yr for CL transitions, with
no significant difference between turn-on and turn-off cases. Taken as
a whole, these findings support an accretion-driven origin of the CL
phenomenon, and provide new insights into the variability of
high-ionization emission lines.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 405 97 Catalog of changing-look (CL) quasars in this work
table5.dat 65 135 CL quasar candidates identified in this work
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See also:
VIII/92 : The FIRST Survey Catalog, Version 2014Dec17 (Helfand+ 2015)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
V/161 : DESI DR1 redshift catalog (DESI Col.+ 2025)
J/ApJS/166/470 : SDSS-Spitzer type I QSOs IR photometry (Richards+, 2006)
J/ApJ/696/870 : Catalina Real-time Transient Survey (CRTS) (Drake+, 2009)
J/ApJ/702/767 : CIV and FeKα Baldwin effects in AGNs (Wu+, 2009)
J/ApJS/194/45 : QSO properties from SDSS-DR7 (Shen+, 2011)
J/ApJ/733/60 : Accretion rate of AGNs from COSMOS surveys (Trump+, 2011)
J/ApJ/750/99 : The Pan-STARRS1 photometric system (Tonry+, 2012)
J/ApJ/777/168 : CIV and SiIV broad abs. line troughs in SDSS (Filiz+, 2013)
J/ApJS/216/4 : SDSS-RM project: technical overview (Shen+, 2015)
J/ApJ/874/8 : Follow-up sp. of SDSS changing-look QSOs (Macleod+, 2019)
J/ApJS/241/34 : The SDSS Reverberation Mapping (SDSS-RM) project (Shen+, 2019)
J/ApJ/883/94 : Optical and UV follow-up of 1ES 1927+654 (Trakhtenbrot+, 2019)
J/ApJ/905/52 : Extreme variability QSOs from SDSS DR16 (Guo+, 2020)
J/ApJS/249/17 : SDSS QSO DR14 spectral properties (Rakshit+, 2020)
J/ApJ/933/180 : TDSS. Changing-look quasars candidates (Green+, 2022)
J/ApJS/272/13 : Changing-look AGN. I. Main sequence transition (Panda+, 2024)
J/ApJS/278/28 : CL-AGN from DESI. II. Stat. properties from DR1 (Guo+, 2025)
http://www.sdss.org/dr18/ : SDSS DR18 homepage
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [SDSS]
6- 24 A19 --- SDSS Unique identifier of SDSS object
(JHHMMSS.ss+DDMMSS.s)
26- 35 F10.6 deg RAdeg [7.4/360] Right Ascension (J2000)
37- 45 F9.6 deg DEdeg [-7.7/56.4] Declination (J2000)
47- 52 F6.4 --- z [0.9/3.3] Spectroscopic redshift
54- 58 I5 d MJD-SDSS [52591/59304] Modified Julian Date of
SDSS spectrum
60- 70 F11.5 d MJD-DESI [59251.96/59737.3] Mean MJD of the
coadded DESI spectra
72- 74 A3 --- Trans Changing state between SDSS and DESI
spectra
76- 78 A3 --- MgII State change in Mg II
80- 82 A3 --- CIII State change in C III
84- 86 A3 --- CIV State change in C IV
88- 90 A3 --- SiIV State change in Si IV
92- 94 A3 --- Lya State change in Lyα
96- 101 F6.3 [10-7W] logLBol-b [45.17/46.73] Log bolometric luminosity
in bright state; erg/s
103- 107 F5.3 [10-7W] e_logLBol-b [0/0.1] Uncertainty in logLBol-b (1)
109- 114 F6.3 [10-7W] logLBol-d [45/46.53] Log bolometric luminosity in
dim state; erg/s
116- 120 F5.3 [10-7W] e_logLBol-d [0/0.3] Uncertainty in logLBol-d (1)
122- 128 F7.2 0.1nm EWMgII-b [4/157]?=-999 Equivalent Width of Mg II
in bright state
130- 136 F7.2 0.1nm e_EWMgII-b [1/9]?=-999 Uncertainty in EWMgII-b (1)
138- 144 F7.2 0.1nm EWMgII-d [9/138]?=-999 Equivalent Width of Mg II
in dim state
146- 152 F7.2 0.1nm e_EWMgII-d [0.8/20]?=-999 Uncertainty in EWMgII-d
(1)
154- 160 F7.2 0.1nm EWCIII-b [24.8/122]?=-999 Equivalent Width of
CIII] in bright state
162- 168 F7.2 0.1nm e_EWCIII-b [0.6/11]?=-999 Uncertainty in EWCIII-b
(1)
170- 176 F7.2 0.1nm EWCIII-d [1.8/80]?=-999 Equivalent Width of CIII]
in dim state
178- 184 F7.2 0.1nm e_EWCIII-d [0.7/18]?=-999 Uncertainty in EWCIII-d
(1)
186- 192 F7.2 0.1nm EWCIV-b [27/237]?=-999 Equivalent Width of C IV
in bright state
194- 200 F7.2 0.1nm e_EWCIV-b [1/15]?=-999 Uncertainty in EWCIV-b (1)
202- 208 F7.2 0.1nm EWCIV-d [10/163]?=-999 Equivalent Width of C IV
in dim state
210- 216 F7.2 0.1nm e_EWCIV-d [1/19]?=-999 Uncertainty in EWCIV-d (1)
218- 222 I5 km/s FWHMMgII-b [2841/10565]?=-999 FWHM of Mg II in
bright state
224- 227 I4 km/s e_FWHMMgII-b [133/3541]?=-999 Uncertainty in
FWHMMgII-b (1)
229- 233 I5 km/s FWHMMgII-d [2816/12919]?=-999 FWHM of Mg II in dim
state
235- 238 I4 km/s e_FWHMMgII-d [159/3921]?=-999 Uncertainty in
FWHMMgII-d (1)
240- 244 I5 km/s FWHMCIV-b [3403/23339]?=-999 FWHM of C IV in
bright state
246- 249 I4 km/s e_FWHMCIV-b [120/8931]?=-999 Uncertainty in
FWHMCIV-b (1)
251- 255 I5 km/s FWHMCIV-d [2820/12755]?=-999 FWHM of C IV in dim
state
257- 261 I5 km/s e_FWHMCIV-d [0/11496]?=-999 Uncertainty in
FWHMCIV-d (1)
263- 269 F7.2 10-20W/m2 FMgII-b [12/787]?=-999 Flux of Mg II in bright
state; 10-17erg/s/cm2
271- 277 F7.2 10-20W/m2 e_FMgII-b [3.9/28]?=-999 Uncertainty in
FMgII-b (1)
279- 285 F7.2 10-20W/m2 FMgII-d [15/532]?=-999 Flux of Mg II in dim
state; 10-17erg/s/cm2
287- 293 F7.2 10-20W/m2 e_FMgII-d [1.7/38]?=-999 Uncertainty in
FMgII-d (1)
295- 301 F7.2 10-20W/m2 FCIII-b [68/700]?=-999 Flux of C III] in bright
state; 10-17erg/s/cm2
303- 309 F7.2 10-20W/m2 e_FCIII-b [5/32]?=-999 Uncertainty in FCIII-b (1)
311- 317 F7.2 10-20W/m2 FCIII-d [2/346]?=-999 Flux of C III] in dim
state; 10-17erg/s/cm2
319- 325 F7.2 10-20W/m2 e_FCIII-d [3.6/38]?=-999 Uncertainty in
FCIII-d (1)
327- 333 F7.2 10-20W/m2 FCIV-b [121/1350]?=-999 Flux of C IV in bright
state; 10-17erg/s/cm2
335- 341 F7.2 10-20W/m2 e_FCIV-b [9/72]?=-999 Uncertainty in FCIV-b (1)
343- 349 F7.2 10-20W/m2 FCIV-d [27/709]?=-999 Flux of C IV in dim
state; 10-17erg/s/cm2
351- 357 F7.2 10-20W/m2 e_FCIV-d [4/34]?=-999 Uncertainty in FCIV-d (1)
359- 364 F6.3 [Msun] logMBH [8.3/10.3] Log adopted fiducial black
hole mass
366- 370 F5.3 [Msun] e_logMBH [0.02/0.4] Uncertainty in LogMBH (1)
372- 377 F6.3 [-] logREdd-b [-2.2/-0.29] Logarithmic Eddington
ratio in bright state
379- 383 F5.3 [-] e_logREdd-b [0/0.1] Uncertainty in logREdd-b (1)
385- 390 F6.3 [-] logREdd-d [-2.6/-0.51] Logarithmic Eddington
ratio in dim state
392- 396 F5.3 [-] e_logREdd-d [0/0.05] Uncertainty in logREdd-d (1)
398- 405 F8.3 mJy F1.4GHz [1.7/5.4]?=-999 FIRST catalog 1.4GHz
radio flux
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Note (1): NULL values are unmeasurable parameters. The errors are
obtained from 200 iterations of the Monte Carlo simulation.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- SDSS Unique identifier of SDSS object
(JHHMMSS.ss+DDMMSS.s)
21- 28 F8.4 deg RAdeg [2.2/358] Right Ascension (J2000)
30- 36 F7.4 deg DEdeg [-2.7/58.7] Declination (J2000)
38- 43 F6.4 --- z [0.94/3.64] Spectroscopic redshift
45- 49 I5 d MJD-SDSS [51816/59292] Modified Julian Date of
SDSS spectrum
51- 61 F11.5 d MJD-DESI [59253.33/59729.37] Mean MJD of the
coadded DESI spectra
63- 65 A3 --- Trans Changing state between SDSS and DESI spectra
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History:
From electronic version of the journal
License: CC-BY-4.0
References:
Guo et al. Paper I. 2024ApJS..270...26G 2024ApJS..270...26G
Guo et al. Paper II. 2025ApJS..278...28G 2025ApJS..278...28G Cat. J/ApJS/278/28
Guo et al. Paper IV. 2025ApJ...995..139G 2025ApJ...995..139G
Chen et al. Paper V. 2026ApJS..282...28C 2026ApJS..282...28C This catalog
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 21-Jul-2026