Improving the selection of changing-look AGNs through multiwavelength photometric variability

López-Navas, E; Sánchez-Sáez, P.; Arévalo, P.; Bernal, S.; Graham, M. J.; Hernández-García, L.; Homan, David; Krumpe, M.; Lamer, G.; Lira, P.; Martínez-Aldama, Mary Loli; Merloni, A.; Rı́os, Susana; Salvato, M.; Stern, Daniel; Tubín-Arenas, D.

doi:10.1093/mnras/stad1893

Cited by 6 publications

(3 citation statements)

References 71 publications

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“…The values of both D n (4000) and Hδ A of 30 local CL-AGNs are reported in Table 3 of Liu et al (2021). For the 17 CL-AGNs recently identified by López-Navas et al (2023), the corresponding Lick indices are obtained from the value-added MPA/JHU catalog (Kauffmann et al 2003;, in which the contamination caused by emission lines has been removed. One can see from the figure that the enlarged sample reinforces the trend that CL-AGNs are associated with an intermediate-age stellar population.…”

Section: Host Galaxiesmentioning

confidence: 99%

Are “Changing-look” Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and Their Hosts? I.

Wang,

Zheng,

Brink

et al. 2023

ApJ

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The nature of the so-called “changing-look” (CL) active galactic nucleus (AGN), which is characterized by spectral-type transitions within ∼10 yr, remains an open question. As the first in our series of studies, we attempt here to understand the CL phenomenon from the view of the coevolution of AGNs and their host galaxies (i.e., if CL-AGNs are at a specific evolutionary stage) by focusing on the SDSS local “partially obscured” AGNs in which the stellar population of the host galaxy can be easily measured in the integrated spectra. A spectroscopic follow-up program using the Xinglong 2.16 m, Lick/Shane 3 m, and Keck 10 m telescopes enables us to identify in total nine CL-AGNs from a sample of 59 candidates selected by their mid-infrared variability. Detailed analysis of these spectra shows that the host galaxies of the CL-AGNs are biased against young stellar populations and tend to be dominated by intermediate-age stellar populations. This motivates us to propose that CL-AGNs are probably particular AGNs at a specific evolutionary stage, such as a transition stage from “feast” to “famine” fueling of the supermassive black hole. In addition, we reinforce the previous claim that CL-AGNs tend to be biased against both a high Eddington ratio and a high bolometric luminosity, suggesting that the disk-wind broad-line-region model is a plausible explanation of the CL phenomenon.

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Section: Host Galaxiesmentioning

confidence: 99%

Are “Changing-look” Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and Their Hosts? I.

Wang,

Zheng,

Brink

et al. 2023

ApJ

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“…Large time domain surveys offer an excellent opportunity to investigate the variability patterns of different AGN classes, and to identify bona fide CL AGNs (e.g., Gezari et al 2017;Frederick et al 2019;Graham et al 2020;Sánchez-Sáez et al 2021a, 2023López-Navas et al 2022, 2023a, 2023b. In this work, we perform a systematic variability study of a large sample of spectroscopically classified AGNs, using light curves from the Zwicky Transient Facility (ZTF; Bellm et al 2019), and demonstrate the viability of this method for the purpose of identifying candidate CL AGNs with a high success rate.…”

Section: Introductionmentioning

confidence: 96%

“…At the same time, the unified model faces significant challenges, particularly with the discovery of a small population of AGNs with emerging/disappearing broad emission lines over timescales of several years. Approximately 150 such changing-look (CL) AGNs have been reported so far, based on Hβ and/or Hα (e.g., LaMassa et al 2015;MacLeod et al 2016MacLeod et al , 2019Ruan et al 2016;Runco et al 2016;Runnoe et al 2016;Yang et al 2018;Wang et al 2019;Green et al 2022;Hon et al 2022;López-Navas et al 2022, 2023bZeltyn et al 2022;Neustadt et al 2023;Guo et al 2024). These CL AGNs demonstrate that the orientation-based unified model might be too simplistic.…”

Section: Introductionmentioning

confidence: 99%

Identifying Changing-look AGNs Using Variability Characteristics

Wang,

Woo,

Gallo

et al. 2024

ApJ

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Changing-look (CL) active galactic nuclei (AGNs), characterized by the appearance/disappearance of broad emission lines in the span of a few years, present a challenge for the AGN unified model, whereby the Type 1 versus Type 2 dichotomy results from orientation effects alone. We present a systematic study of a large sample of spectroscopically classified AGNs, using optical variability data from the Zwicky Transient Facility (ZTF) as well as follow-up spectroscopy data. We demonstrate that Type 1 and Type 2 AGNs can be neatly separated on the basis of the variability metric σ QSO, which quantifies the resemblance of a light curve to a damped random walk model. For a small subsample, however, the ZTF light curves are inconsistent with their previous classification, suggesting the occurrence of a CL event. Specifically, we identify 35 (12) turn-on (turn-off) CL AGN candidates at z < 0.35. Based on follow-up spectroscopy, we confirm 17 (4) turn-on (turn-off) CL AGNs out of 21 (5) candidates, representing a high success rate for our method. Our results suggest that the occurrence rate of CL AGNs is ∼0.3% over timescales of 5–20 yr, and confirm that the CL transition typically occurs at an Eddington ratio of ≲0.01.

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SDSS1335+0728: The awakening of a ∼10⁶ M_⊙ black hole

Sánchez-Sáez,

Hernández-García,

Bernal

et al. 2024

A&A

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The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a $ odot $ black hole (BH) that is currently in the process of `turning on'. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift /UVOT observations) is four times brighter than the flux reported by GALEX in 2004 ; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1$-$W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the OIII line increased its flux $ 3.6$ years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. We conclude that the variations observed in SDSS1335+0728 could be either explained by a $ odot $ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGN observed in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour.

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Improving the selection of changing-look AGNs through multiwavelength photometric variability

Cited by 6 publications

References 71 publications

Are “Changing-look” Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and Their Hosts? I.

Are “Changing-look” Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and Their Hosts? I.

Identifying Changing-look AGNs Using Variability Characteristics

SDSS1335+0728: The awakening of a ∼10⁶ M_⊙ black hole

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Improving the selection of changing-look AGNs through multiwavelength photometric variability

Cited by 6 publications

References 71 publications

Are “Changing-look” Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and Their Hosts? I.

Are “Changing-look” Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and Their Hosts? I.

Identifying Changing-look AGNs Using Variability Characteristics

SDSS1335+0728: The awakening of a ∼106 M⊙ black hole

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SDSS1335+0728: The awakening of a ∼10⁶ M_⊙ black hole