J/ApJ/961/172 Optically variable AGNs with double-peaked emission (Ward+, 2024)
Panic at the ISCO: time-varying double-peaked broad lines from evolving
accretion disks are common among optically variable AGNs.
Ward C., Gezari S., Nugent P., Kerr M., Eracleous M., Frederick S.,
Hammerstein E., Graham M.J., van Velzen S., Kasliwal M.M., Laher R.R.,
Masci F.J., Purdum J., Racine B., Smith R.
<Astrophys. J., 961, 172 (2024)>
=2024ApJ...961..172W 2024ApJ...961..172W
ADC_Keywords: Active gal. nuclei; Spectra, optical; Photometry; Redshifts;
Radio sources; Morphology
Keywords: Active galactic nuclei ; Tidal disruption ; Galaxy accretion disks ;
Radio active galactic nuclei
Abstract:
About 3%-10% of Type I active galactic nuclei (AGNs) have
double-peaked broad Balmer lines in their optical spectra originating
from the motion of gas in their accretion disk. Double-peaked profiles
arise not only in AGNs, but occasionally appear during optical flares
from tidal disruption events and changing-state AGNs. In this paper,
we identify 250 double-peaked emitters (DPEs) among a parent sample of
optically variable broad-line AGNs in the Zwicky Transient Facility
(ZTF) survey, corresponding to a DPE fraction of 19%. We model spectra
of the broad Hα emission-line regions and provide a catalog of
the fitted accretion disk properties for the 250 DPEs. Analysis of
power spectra derived from the 5yr ZTF light curves finds that DPE
light curves have similar amplitudes and power-law indices to other
broad-line AGNs. Follow-up spectroscopy of 12 DPEs reveals that ∼50%
display significant changes in the relative strengths of their red and
blue peaks over long 10-20yr timescales, indicating that broad-line
profile changes arising from spiral arm or hotspot rotation are common
among optically variable DPEs. Analysis of the accretion disk
parameters derived from spectroscopic modeling provides evidence that
DPEs are not in a special accretion state, but are simply normal
broad-line AGNs viewed under the right conditions for the accretion
disk to be easily visible. We include inspiraling supermassive black
hole binary candidate SDSSJ1430+2303 in our analysis, and discuss how
its photometric and spectroscopic variability is consistent with the
disk-emitting AGN population in the ZTF survey.
Description:
For our variability analysis we have used observations from the ZTF
survey (Bellm+ 2019PASP..131a8002B 2019PASP..131a8002B; Graham+ 2019PASP..131g8001G 2019PASP..131g8001G;
Dekany+ 2020PASP..132c8001D 2020PASP..132c8001D), an ongoing optical survey which began in
2018 March and achieves single-epoch limiting magnitudes of ∼21 in the
g, r, and i bands over a survey footprint of 23675deg2. For our
sample of 250 double-peaked emitters (DPEs), we present both
power-spectrum analysis of ZTF light curves and spectroscopically
derived disk geometries from fits to the double-peaked line profiles.
To produce a parent sample of 1549 optically variable broad-line AGNs,
we started with the 5000 variable AGNs identified in ZTF time-domain
survey data in Ward+ (2021ApJ...913..102W 2021ApJ...913..102W) and required among other
criteria that the AGN have redshifts z<0.4.
In order to find the AGNs with double-peaked broad lines among the
sample of 1549 broad-line AGNs, we modeled the archival SDSS spectra
of the AGNs.
See Section 2.
We undertook a search for radio emission from the DPE and control AGN
samples in the Karl G. Jansky VLASS (see Gordon+ 2021, J/ApJS/255/30).
This survey covers a total of 33885deg2 in the 2-4GHz range with an
angular resolution of ∼2.5".
We also searched for radio emission in the Rapid ASKAP Continuum
Survey (RACS), with first epoch observations covering the whole
southern sky to +41deg decl. with the Australia Square Kilometre Array
Pathfinder at a central wavelength of 887.5MHz
(Hale+ 2021, J/other/PASA/38.58).
See Section 4.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 128 250 Properties of the 250 double-peaked emitter (DPE)
candidates from ZTF
table2.dat 118 244 *Best-fit accretion disk parameters
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Note on table2.dat: From modeling the Hα broad-line regions of the
AGN with the circular accretion disk model from
Chen & Halpern 1989ApJ...344..115C 1989ApJ...344..115C
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Description of file:
The directory "ZTF-DPEs-main" was downloaded in .zip directly at:
https://github.com/charlotteaward/ZTF-DPEs/
See also:
J/ApJ/599/886 : Emission lines of radio-loud AGN (Eracleous+, 2003)
J/AJ/126/1720 : ugriz and Hα of double-peaked AGN (Strateva+, 2003)
J/ApJ/743/156 : NEOWISE obs. of NEOs: preliminary results (Mainzer+, 2011)
J/A+A/559/A10 : Arp 102B spectral optical monitoring (Shapovalova+, 2013)
J/ApJ/792/30 : NEOWISE magnitudes for near-Earth objects (Mainzer+, 2014)
J/ApJS/217/26 : Lick AGN monitoring 2011: light curves (Barth+, 2015)
J/ApJS/233/17 : Swift/BAT AGN spectroscopic survey. V. X-ray (Ricci+, 2017)
J/ApJ/880/120 : Phot. of the tidal disruption event PS18kh (Holoien+, 2019)
J/A+A/631/A147 : Transient processing & analysis using AMPEL (Nordin+, 2019)
J/ApJ/903/31 : Phot. AT 2018hyz with Swift XRT, UVOT & Swope (Hung+, 2020)
J/other/Sci/373.789 : optical variability of AGNs (Burke+, 2021)
J/ApJS/255/30 : VLASS QL Ep.1 Catalog, CIRADA version (Gordon+, 2021)
J/other/PASA/38.58 : Rapid ASKAP Continuum Survey. II. RACS cat. (Hale+, 2021)
J/ApJ/910/125 : Follow-up photometry of ASASSN-14ko (Payne+, 2021)
J/A+A/664/A117 : 677 AGN of VST-COSMOS (De Cicco+, 2022)
http://www.sdss.org/ : SDSS homepage
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- ZTF ZTF identifier (ZTFYYaaaaaaa)
14- 15 I2 h RAh [0/23] Hour of Right Ascension (J2000)
17- 18 I2 min RAm Minute of Right Ascension (J2000)
20- 25 F6.3 s RAs Second of Right Ascension (J2000)
27 A1 --- DE- Sign of the Declination (J2000)
28- 29 I2 deg DEd Degree of Declination (J2000)
31- 32 I2 arcmin DEm Arcminute of Declination (J2000)
34- 39 F6.3 arcsec DEs Arcsecond of Declination (J2000)
41- 46 F6.4 --- z [0.0076/0.4]? SDSS spectroscopic redshift
48- 51 F4.1 [-] logAmp [-4.2/-1.2] Log amplitude (1)
53- 55 F3.1 [-] E_logAmp [0/0.6] Upper uncertainty in logAmp
57- 59 F3.1 [-] e_logAmp [0/1.1] Lower uncertainty in logAmp
61- 63 F3.1 --- PL [0/5] Power Law index (1)
65- 67 F3.1 --- E_PL [0.1/3.9] Upper uncertainty in PL
69- 71 F3.1 --- e_PL [0/3.1] Lower uncertainty in PL
73- 77 F5.1 yr-1 Turn [0.1/349.5] Turnover frequency (1)
79- 83 F5.1 yr-1 E_Turn [0.3/336.9] Upper uncertainty in Turn
85- 89 F5.1 yr-1 e_Turn [0.1/328.2] Lower uncertainty in Turn
91- 96 F6.2 mJy E1 [0.67/470]? VLASS epoch 1 (2017-2018) radio
flux density (2)
98- 101 F4.2 mJy e_E1 [0.19/3.1]? Uncertainty in E1 (2)
103- 108 F6.2 mJy E2 [0.96/405]? VLASS epoch 2 (2010-2021) radio
flux density (2)
110- 113 F4.2 mJy e_E2 [0.18/0.9]? Uncertainty in E2 (2)
115- 120 F6.2 mJy RACS [2.19/558]? RACS-low 34cm epoch 1 survey flux
density (2)
122- 126 F5.2 mJy e_RACS [0.8/40]? Uncertainty in RACS (2)
128 A1 --- f_RACS [d] Indicates RACS is not within surveyed
region
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Note (1): From modeling of the power spectrum derived from the g-band
ZTF light curve (see Section 3).
Note (2): Blanks indicate non-detections.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- ZTF ZTF identifier (ZTFYYaaaaaaa)
14- 17 I4 --- xi1 [50/1960] Inner gravitational radius, ξ1
19- 22 I4 --- E_xi1 [10/1320] Upper uncertainty in xi1
24- 27 I4 --- e_xi1 Lower uncertainty in xi1
29- 32 I4 --- xi2 [310/3990] Outer gravitational radius, ξ2
34- 37 I4 --- E_xi2 [10/1980] Upper uncertainty in xi2
39- 42 I4 --- e_xi2 Lower uncertainty in xi2
44- 47 I4 km/s sigma [80/3000] Turbulent broadening
49- 52 I4 km/s E_sigma [0/1020] Upper uncertainty in sigma
54- 57 I4 km/s e_sigma Lower uncertainty in sigma
59- 60 I2 deg i [0/53] Inclination angle
62- 64 I3 deg E_i [1/294] Upper uncertainty in i
66- 68 I3 deg e_i Lower uncertainty in i
70- 72 F3.1 --- q [0.8/2.5] Emissivity power law index
74- 76 F3.1 --- E_q [0/1.1] Upper uncertainty in q
78- 80 F3.1 --- e_q Lower uncertainty in q
82- 83 I2 deg w [2/80] Spiral arm width
85- 86 I2 deg E_w [0/33] Upper uncertainty in w
88- 89 I2 deg e_w Lower uncertainty in w
91 I1 --- As [0/8] Spiral arm amplitude expressed as contrast
ratio
93 I1 --- E_As [1/5] Upper uncertainty in As
95 I1 --- e_As Lower uncertainty in As
97- 99 I3 deg psi [0/360] Spiral arm pitch angle
101- 102 I2 deg E_psi [10/70] Upper uncertainty in psi
104- 106 I3 deg e_psi Lower uncertainty in psi
108- 110 I3 deg phi [0/360] Spiral arm phase
112- 114 I3 deg E_phi [10/360] Upper uncertainty in phi
116- 118 I3 deg e_phi Lower uncertainty in phi
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History:
From electronic version of the journal for Tables 1 and 2
* Directory ZTF-DPEs-main downloaded at:
https://github.com/charlotteaward/ZTF-DPEs/
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 08-Apr-2026