J/ApJ/966/85 CL-AGNs with repeated sp. of SDSS-V first year (Zeltyn+, 2024)
Exploring changing-look active galactic nuclei with the Sloan Digital Sky Survey
V: first year results.
Zeltyn G., Trakhtenbrot B., Eracleous M., Yang Q., Green P.,
Anderson S.F., LaMassa S., Runnoe J., Assef R.J., Bauer F.E., Brandt W.N.,
Davis M.C., Frederick S.E., Fries L.B., Graham M.J., Grogin N.A.,
Guolo M., Hernandez-Garcia L., Koekemoer A.M., Krumpe M., Liu X.,
Martinez-Aldama M.L., Ricci C., Schneider D.P., Shen Y., Sniegowska M.,
Temple M.J., Trump J.R., Xue Y., Brownstein J.R., Dwelly T., Morrison S.,
Bizyaev D., Pan K., Kollmeier J.A.
<Astrophys. J., 966, 85 (2024)>
=2024ApJ...966...85Z 2024ApJ...966...85Z
ADC_Keywords: Active gal. nuclei; QSOs; Spectra, optical; Redshifts; Black holes
Keywords: Quasars ; Supermassive black holes
Abstract:
"Changing-look" active galactic nuclei (CL-AGNs) challenge our basic
ideas about the physics of accretion flows and circumnuclear gas
around supermassive black holes. Using first-year Sloan Digital Sky
Survey V (SDSS-V) repeated spectroscopy of nearly 29,000 previously
known active galactic nuclei (AGNs), combined with dedicated follow-up
spectroscopy, and publicly available optical light curves, we have
identified 116 CL-AGNs where (at least) one broad emission line has
essentially (dis-)appeared, as well as 88 other extremely variable
systems. Our CL-AGN sample, with 107 newly identified cases, is the
largest reported to date, and includes ∼0.4% of the AGNs reobserved in
first-year SDSS-V operations. Among our CL-AGNs, 67% exhibit dimming
while 33% exhibit brightening. Our sample probes extreme AGN spectral
variability on months to decades timescales, including some cases of
recurring transitions on surprisingly short timescales (≲2 months in
the rest frame). We find that CL events are preferentially found in
lower-Eddington-ratio (fEdd) systems: Our CL-AGNs have a fEdd
distribution that significantly differs from that of a carefully
constructed, redshift- and luminosity-matched control sample
(Anderson-Darling test yielding pAD∼6x10-5; median fEdd∼0.025
versus 0.043). This preference for low fEdd strengthens previous
findings of higher CL-AGN incidence at lower fEdd, found in smaller
samples. Finally, we show that the broad MgII emission line in our
CL-AGN sample tends to vary significantly less than the broad Hβ
emission line. Our large CL-AGN sample demonstrates the advantages and
challenges in using multi-epoch spectroscopy from large surveys to
study extreme AGN variability and physics.
Description:
Our sample and analysis of strongly variable AGNs are based on optical
spectroscopy obtained during the first year of SDSS-V of AGNs
spectroscopically observed during the previous four SDSS generations
(SDSS-I--IV, Data Release 16, DR16; Ahumada+ 2020, V/154).
Our main data set consists of medium-resolution (R∼2000) spectra
obtained through the Black Hole Mapper (BHM) program within the first
year of operations of SDSS-V, covering 2020 October through 2021 June.
These spectra were acquired using the Baryon Oscillation Spectroscopic
Survey (BOSS) spectrograph, mounted on the Sloan Foundation 2.5m
telescope at the Apache Point Observatory.
See Section 2.1.
In addition to the SDSS-V spectroscopy, we performed an extensive
spectroscopic effort to corroborate the nature of the identified
CL-AGN candidates, using various facilities. Additional optical
spectroscopy was obtained with the 2m Faulkes Telescope North (FTN)
and South (FTS) facilities, which are part of the Las Cumbres
Observatory network (LCOGT); the Low-Resolution Spectrograph 2 (LRS2)
on the 10m Hobby-Eberly Telescope (HET) at McDonald Observatory; and
the Double Spectrograph (DBSP) on the 5.1m Hale Telescope at the
Palomar Observatory. Spectra were obtained through either long slits
with widths of either 2" (FTN and FTS) or 1.5" (Hale), or with
dynamic, seeing-matched apertures of 1.7"-2.5" (HET), and calibrated
using standard stars observed during the corresponding nights.
See Section 2.4.1.
To further corroborate and examine our candidates, we used publicly
available optical photometric light curves obtained through the Zwicky
Transient Facility (ZTF), the Asteroid Terrestrial-impact Last Alert
System (ATLAS), the Catalina Real-time Transient Survey (CRTS), and
the Pan-STARRS1 (PS1) data sets and compared these with synthetic
photometry derived from the candidates' (SDSS) spectra.
See Section 2.4.2.
We used publicly available data from the Wide-field Infrared Survey
Explorer (WISE) to create IR light curves for our candidates in the W1
(∼3.4um) and W2 (∼4.6um) bands, with a cadence of about 6 months.
See section 2.4.3.
Our final core sample consists of 113 robust CL-AGN candidates, listed
in Table 5.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table5.dat 114 204 Robust "Changing-look" active galactic nuclei
(CL-AGNs) and extremely variable quasars (EVQs)
identified in this work
table6.dat 61 113 Spectral measurements of CL-AGNs
table7.dat 33 109 Follow-up observations for 73 sources
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See also:
VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
II/328 : AllWISE Data Release (Cutri+ 2013)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+, 2016)
IX/57 : The Chandra Source Catalog (CSC), Release 2.0 (Evans+, 2019)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
VII/289 : SDSS quasar catalog, sixteenth data release (DR16Q) (Lyke+, 2020)
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/716/530 : Mid-IR variability from the SDWFS (Kozlowski+, 2010)
J/ApJ/753/106 : Quasar variability with SDSS & POSS imaging (MacLeod+, 2012)
J/A+A/560/A104 : UV variability of quasars (Meusinger+, 2013)
J/ApJ/779/109 : Long-term monitoring of NGC 5548 (Peterson+, 2013)
J/ApJ/792/30 : NEOWISE magnitudes for near-Earth objects (Mainzer+, 2014)
J/ApJS/219/1 : Catalog of Type-1 AGNs from SDSS-DR7 (Oh+, 2015)
J/ApJS/216/4 : SDSS-RM project: technical overview (Shen+, 2015)
J/MNRAS/463/296 : PanSTARRS-1 slow-blue nuclear hypervar. (Lawrence+, 2016)
J/ApJ/854/160 : SDSS and DES long-term extreme var. QSOs (Rumbaugh+, 2018)
J/ApJ/852/72 : LFs of tidal disruption flares (van Velzen, 2018)
J/ApJ/886/42 : Reverberation mapping & opt. spectra of AGNs (Du+, 2019)
J/ApJ/874/8 : Follow-up sp. of SDSS changing-look QSOs (Macleod+, 2019)
J/ApJ/886/150 : VRI and K-band light curves of type 1 AGNs (Minezaki+, 2019)
J/ApJS/241/34 : SDSS Reverberation Mapping (SDSS-RM) project (Shen+, 2019)
J/ApJ/883/94 : Optical & UV follow-up of 1ES 1927+654 (Trakhtenbrot+, 2019)
J/ApJ/887/15 : Xinglong sp. of two changing-look SDSS AGNs (Wang+, 2019)
J/MNRAS/491/4925 : Changing-state quasars with CRTS (Graham+, 2020)
J/ApJ/905/52 : Extreme variability QSOs from SDSS DR16 (Guo+, 2020)
J/ApJ/901/55 : SDSS-RM project: MgII lags from 4yrs obs. (Homayouni+, 2020)
J/MNRAS/503/2583 : Survey for z< 0.04 CLAGNs (Senarath+, 2021)
J/ApJ/933/180 : TDSS. Changing-look quasars candidates (Green+, 2022)
J/ApJS/261/5 : BASS. XXV. DR2 AGNs BH masses (Mejia-Restrepo+, 2022)
http://irsa.ipac.caltech.edu/Missions/ztf.html : ZTF data on IRSA
http://www.sdss.org/ : SDSS-V homepage
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Name SDSS Identifier (JHHMMSS.ss+DDMMSS.s)
21- 28 F8.6 --- z [0.058/2.8] Redshift
30- 34 I5 d First [51782/58523] Modified Julian Date of earliest
spectrum
36- 40 I5 d Last [59146/59387] Modified Julian Date of last spectrum
42- 50 A9 --- Class Event type (1)
52- 57 F6.2 --- CHa [-19/6.7]? Ha emission line change parameter (2)
59- 66 F8.2 --- CHb [-1578/6]? Hb emission line change parameter (2)
68- 73 F6.2 --- CMgII [-34/8.6]? MgII emission line change parameter (2)
75- 79 F5.2 --- CCIII [-6.8/5.6]? CCIII emission line change parameter (2)
81- 84 F4.2 --- CCIV [1.7/6.7]? CCIV emission line change parameter (2)
86 I1 --- Spec [0/2]? Ancillary spectroscopy (3)
88 I1 --- Opt [1/2] Ancillary optical photometry (4)
90 I1 --- WISE [0/2]? Ancillary WISE data (5)
92-114 A23 --- Notes References (6)
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Note (1): Event type as follows:
CL-AGN = Changing-look AGN (non-RM; 113 occurrences)
CL-AGN RM = Changing-look AGN (RM; 3 occurrences)
EVQ = Extremely variable quasar (88 occurrences)
Note (2): The line variation parameter, as defined by Equation 1:
C(line)=F2/F1-Δ(F2/F1)
where F2/F1 is the ratio between the (continuum-subtracted) line
fluxes for the two specific epochs, with F2 defined to be the higher
flux of the two, and is the 1σ equivalent uncertainty on the
line flux ratio, propagated from the two error spectra.
For CL-AGNs from our core sample ("Class": CL-AGN), these values are
calculated using the decomposed, narrow-line subtracted spectra; For
EVQs and RM CL-AGNs, these values are calculated directly from the
observed spectra.
Note (3): Code as follows:
0 = no follow-up spectroscopy taken;
1 = follow-up spectroscopy is inconclusive;
2 = follow-up spectroscopy confirms the SDSS-V spectroscopy.
Note (4): Code as follows:
1 = the available photometric data are irrelevant or inconclusive
for our work;
2 = photometric data confirm concurrent spectral changes.
Note (5): Code as follows:
0 = no relevant WISE data;
1 = trend in WISE light curve does not match concurrent spectral changes;
2 = trend in WISE light curve matches concurrent spectral changes.
Note (6): Note as follows:
new = Object does not appear in any previous work,
to the best of the authors' knowledge;
L15 = Noted by LaMassa et al. (2015ApJ...800..144L 2015ApJ...800..144L)
M16 = Noted by MacLeod et al. (2016MNRAS.457..389M 2016MNRAS.457..389M)
R16 = Noted by Ryan et al. (2016ApJ...826..188R 2016ApJ...826..188R)
Y18 = Noted by Yang et al. (2018ApJ...862..109Y 2018ApJ...862..109Y)
H19 = Noted by Hutsemekers et al. (2019A&A...625A..54H 2019A&A...625A..54H)
M19 = Noted by MacLeod et al. (2019, J/ApJ/874/8)
G20 = Noted by Graham et al. (2020, J/MNRAS/491/4925)
G22 = Noted by Green et al. (2022, J/ApJ/933/180)
Z22 = Noted by Zeltyn et al. (2022ApJ...939L..16Z 2022ApJ...939L..16Z)
G24 = Noted by Guo et al. (2024ApJS..270...26G 2024ApJS..270...26G)
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Name SDSS Identifier (JHHMMSS.ss+DDMMSS.s)
21- 28 F8.6 --- z [0.058/2.4] Redshift
30- 33 A4 --- SpCom Emission line complex which spectral
measurement are based on ("Ha" or "MgII")
35- 38 F4.1 --- logL [40.7/45.3] Luminosity used for mass
estimate (Ha or MgII at 3000Å)
40- 44 I5 km/s FWHM [1475/34793] Emission line FWHM
46- 49 F4.2 [Msun] logMBH [6.38/9.5] Estimated black hole mass
51- 54 F4.1 [10-7W] logLbol [42.6/46] Bolometric luminosity (1)
56- 61 F6.3 [-] logfEdd [-2.75/-0.33] Eddington ratio
--------------------------------------------------------------------------------
Note (1): If SpCom = Ha: Luminosity at 5100Å times 9.26;
If "SpCom" = MgII: Luminosity at 3000Å times 5.15.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Name SDSS Identifier (JHHMMSS.ss+DDMMSS.s)
21- 27 A7 --- Obs Facility where spectrum was taken (1)
29- 33 I5 d MJD [59329/60088] Modified Julian Date of the epoch
of the spectrum
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Note (1): Facility as follows:
LCOGT = the 2m Faulkes Telescope North (FTN) and South (FTS)
facilities, which are part of the Las Cumbres Observatory network;
HET = the 10m Hobby-Eberly Telescope at McDonald Observatory;
Palomar = the 5.1m Hale Telescope at the Palomar Observatory.
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Aug-2026