Systematic Research of Low-redshift Optically Selected SDSS Type 2 AGNs but with Apparent Long-term Optical Variabilities from Catalina Sky Survey. I. Data Sample and Basic Results

Zhang, Xueguang

doi:10.3847/1538-4365/acdb59

Cited by 3 publications

(2 citation statements)

References 119 publications

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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%

“…Nevertheless, some spectroscopically classified Type 2 AGNs are known to exhibit some non-negligible levels of variability (Barth et al 2014;López-Navas et al 2023a;Zhang 2023), with an occurrence rate of ∼10%. Some of these are likely misclassified, weak, Type 1 AGNs, whereas others have been identified as CL AGNs based on follow-up spectroscopic observations (López-Navas et al 2022, 2023b, hereafter LN22 andLN23b, respectively).…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Identifying Changing-look AGNs Using Variability Characteristics

Wang,

Woo,

Gallo

et al. 2024

ApJ

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AGN populations in the local Universe: Their alignment with the main sequence, stellar population characteristics, accretion efficiency, and the impact of AGN feedback

Mountrichas,

Ruiz,

Georgantopoulos

et al. 2024

A&A

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In this study, we used a sample of 338 galaxies ---within the redshift range of $ 0.02<z<0.1$ drawn from the Sloan Digital Sky Survey (SDSS)--- for which there are available classifications based on their emission line ratios. We identified and selected Compton-thick (CT) AGN through the use of X-ray and infrared luminosities at $12\ m$. We constructed the spectral energy distributions (SEDs) for all sources and fit them using the CIGALE code to derive properties related to both the AGN and host galaxies. Employing stringent criteria to ensure the reliability of SED measurements, our final sample comprises 14 CT AGN, 118 Seyfert 2 (Sy2), 82 composite, and 124 low-ionization nuclear emission-line regions (LINER) galaxies. Our analysis reveals that, irrespective of their classification, the majority of the sources lie below the star-forming main sequence (MS). Additionally, a lower level of AGN activity is associated with a closer positioning to the MS. Using the D$_n$4000 spectral index as a proxy for the age of stellar populations, we observe that, compared to other AGN classes, LINERs exhibit the oldest stellar populations. Conversely, CT sources are situated in galaxies with the youngest stellar populations. Furthermore, LINER and composite galaxies tend to show the lowest accretion efficiency, while CT AGN, on average, display the most efficient accretion among the four AGN populations. Our findings are consistent with a scenario in which the different AGN populations might not originate from the same AGN activity burst. Early triggers in gas-rich environments can create high-accretion-rate supermassive black holes (SMBHs), leading to a progression from CT to Sy2, while later triggers in gas-poor stages result in low-accretion-rate SMBHs like those found in LINERs.

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A normal broad line AGN SDSS J1617+0638 as the host galaxy of a central tidal disruption event

Zhang

2024

Monthly Notices of the Royal Astronomical Society: Letters

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In this manuscript, strong clues are reported to support the normal broad line AGN SDSS J1617+0638as the host galaxy harboring a central tidal disruption event (TDE). Through the optical flare in the CSS 8.5years-long light curve and the none-variability in the up-to-date ASAS-SN light curves, the theoretical TDE model described by the MOSFIT code can be applied in SDSS J1617+0638. Meanwhile, considering the assumed central TDE expected continuum emissions not strong enough to describe the continuum emissions in the SDSS spectrum of SDSS J1617+0638, an additional power law component from pre-existing AGN activity should be necessary in SDSS J1617+0638. Furthermore, considering the short time duration to the observed date for the SDSS spectrum from the starting time of the assumed central TDE in SDSS J1617+0638, TDE model expected accreting mass only about 0.03M⊙ can lead to few effects of TDEs debris on the observed broad emission lines in the SDSS spectrum of SDSS J1617+0638, indicating the TDE model determined BH mass simply consistent with the virial BH mass by broad emission lines, as determined results in SDSS J1617+0638. Therefore, through both the photometric variability and the spectroscopic results, a central TDE can be preferred in the normal broad line AGN SDSS J1617+0638 with pre-existing central AGN activity and pre-existing broad emission line regions.

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Systematic Research of Low-redshift Optically Selected SDSS Type 2 AGNs but with Apparent Long-term Optical Variabilities from Catalina Sky Survey. I. Data Sample and Basic Results

Cited by 3 publications

References 119 publications

Identifying Changing-look AGNs Using Variability Characteristics

Identifying Changing-look AGNs Using Variability Characteristics

AGN populations in the local Universe: Their alignment with the main sequence, stellar population characteristics, accretion efficiency, and the impact of AGN feedback

A normal broad line AGN SDSS J1617+0638 as the host galaxy of a central tidal disruption event

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