A Systematic Analysis of Stellar Populations in the Host Galaxies of Changing-look AGNs

Jin, Jia; Wu, Xue-Bing; Feng, Xiaotong

doi:10.3847/1538-4357/ac410c

Cited by 9 publications

(17 citation statements)

References 132 publications

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“…This negative trend is also found in a single CLAGN, but its slope may be different for different sources. The average Balmer decrement for 16 CLAGNs in turn-on state from Jin et al (2022) is Hα/Hβ = 4.73, which is also statistically higher than that of normal, bright AGNs. Except for the evident deviation of Hα/Hβ for sources with λ Edd < 1%-2%, the slope of the Hα/Hβ-λ Edd correlation also becomes steeper in CLAGNs of 3C and 1ES 1927+654 at lower Eddington ratios.…”

Section: Resultsmentioning

confidence: 76%

“…For CLAGNs, we include 6 sources with multiple optical spectral observations (NGC 5548, NGC 4151, 3C 390.3, NGC 3516, Mrk 1018, and1ES 1927+654) and 16 sources with only two observations from Jin et al (2022). We note that only the emission-line intensities at a high state (or turn-on state) with evident broad lines are adopted in our work because the emission lines are weak or absent in a low state (or turn-off state).…”

Section: Samplementioning

confidence: 99%

“…The data of 1ES 1927+654 are selected from Li et al (2022). For CLAGNs with only two spectra in Jin et al (2022), we exclude the objects observed by the XingLong Telescope for bad spectral quality and several sources with very large differences of velocity even in active state (i.e., FWHM(Hβ)/FWHM (Hα) 1.5 or FWHM(Hα)/FWHM(Hβ) 1.5). The source ZTF18aajupnt is considered to be a candidate for a tidal disruption event (Jin et al 2022), which is also removed from our sample.…”

Section: Samplementioning

confidence: 99%

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Steep Balmer Decrement in Weak AGNs May Not Be Caused by Dust Extinction: Clues from Low-luminosity AGNs and Changing-look AGNs

Wu¹,

Wu²,

Xue³

et al. 2023

ApJ

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The hydrogen Balmer decrement (e.g., Hα/Hβ) is widely adopted as an indicator of the internal reddening of active galactic nuclei (AGNs). This is challenged by some low-luminosity AGNs and changing-look AGNs (CLAGNs), which have steep Balmer decrement but without strong evidence for absorption. We compile a sample of normal AGNs and CLAGNs with a wider distribution of bolometric Eddington ratio (λ Edd = L bol/L Edd) and find a strong negative correlation between Hα/Hβ and λ Edd, which suggests that the Balmer decrement is also accretion-rate dependent. We further explore the Balmer decrement based on the photoionization model using the Cloudy code by considering spectral energy distribution from the accretion disk with different accretion rates (e.g., disk/corona and truncated disk at high and low Eddington ratios, respectively). Both the standard disk and truncated disk predict a negative correlation of Hα/Hβ–λ Edd, where the relation is steeper in the case of the truncated disk. The negative correlations are also explored in two single CLAGNs. The measured negative correlation of Hα/Hβ–λ Edd is mainly caused by the lower responsivity ( d log L line / d log L cont ) in Hα relative to that in Hβ due to the larger optical depth in the former. We propose that the steep Balmer decrements in low Eddington ratio AGNs (e.g., some Seyferts 1.5–1.9 and CLAGNs) are not simply caused by absorption but mainly caused by the relatively low flux of ionizing photons.

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Section: Resultsmentioning

confidence: 76%

Section: Samplementioning

confidence: 99%

Section: Samplementioning

confidence: 99%

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Steep Balmer Decrement in Weak AGNs May Not Be Caused by Dust Extinction: Clues from Low-luminosity AGNs and Changing-look AGNs

Wu¹,

Wu²,

Xue³

et al. 2023

ApJ

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“…in small galaxies (Baldassare et al 2020). Many works have shown that AGNs share the same M BH − σ * relation as quiescent galaxies (Greene & Ho 2004;Greene et al 2008;Jin et al 2022), but some investigations suggest that this relation may change among different types of galaxies (Graham & Li 2009;Rakshit et al 2017;Dodd et al 2021). So it is a good opportunity to verify this relation for this dual core system.…”

Section: ~=mentioning

confidence: 92%

Velocity Offset Between Emission and Absorption Lines Might Be an Effective Indicator of a Dual Core System

Zheng¹,

Liu²,

Zhang³

et al. 2023

ApJ

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This paper presents the detection of a significant velocity offset between the emission and absorption lines of a dual core system in SDSS J155708.82+273518.74 (=SDSS J1557). The photometric image of SDSS J1557 exhibits two clear cores with a projected separation of ∼2.″2 (4.9 kpc) determined by GALFIT. Based on the applications of the commonly accepted pPXF code with 636 theoretical SSP templates, the host galaxy contribution can be well determined. Then, the emission-line features of SDSS J1557 can be well measured after subtraction of the host starlight. It is found that the velocity offset of emission lines with respect to absorption lines reaches 458 ± 13 km s−1. According to a Baldwin–Phillips–Terlevich diagram, SDSS J1557 is a composite galaxy. In addition, SDSS J1557 can well fit the M BH − σ * relation of bulges, and a galaxy merger would not change this relation. Two reasonable models (an AGN-driven outflow versus a dual core system) are discussed to explain this velocity offset. The model of an AGN-driven outflow fails to interpret the systematic redshift of the emission lines and similar velocity offsets for the various emission lines of SDSS J1557. Instead, the significant velocity offset between the emission and absorption lines might be an effective indicator of a dual core system.

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“…With a large number of repeat spectral observations of SDSS and LAMOST, we can investigate the spectroscopic variability of quasars on both short and long timescales. Moreover, these multiepoch spectra give us a good chance to search for unusual AGNs such as changing-look AGNs (CL-AGNs; e.g., Runco et al 2016;Yang et al 2018;MacLeod et al 2019;Guo et al 2019;) and uncover the possible physical mechanism behind them (MacLeod et al 2019;Frederick et al 2019;Jin et al 2022).…”

Section: Quasar Identificationmentioning

confidence: 99%

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Quasar Survey: Quasar Properties from Data Releases 6 to 9

Jin¹,

Wu²,

Fu³

et al. 2023

ApJS

Self Cite

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We report the fourth installment in the series of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) quasar survey, which includes quasars observed between 2017 September and 2021 June. There are in total 13,066 quasars reliably identified, of which 6685 are newly discovered that are not reported in the Sloan Digital Sky Survey (SDSS) DR14 quasar catalog or Million Quasars catalog. Because LAMOST does not provide accurate absolute flux calibration, we recalibrate the spectra with the SDSS/Pan-STARRS1 multiband photometric data. The emission-line properties of Hα, Hβ, Mg ii, and C iv and the continuum luminosities are measured by fitting the recalibrated spectra. We also estimate the single-epoch virial black hole masses (M BH) using the derived emission-line and continuum parameters. This is the first time that the emission-line and continuum fluxes were estimated based on LAMOST recalibrated quasar spectra. The catalog and spectra for these quasars are available online. After the 9 yr LAMOST quasar survey, there are in total 56,175 identified quasars, of which 24,127 are newly discovered. The LAMOST quasar survey not only discovers a great number of new quasars but also provides a database for investigating the spectral variability of the quasars observed by both LAMOST and SDSS and finding rare quasars, including changing-look quasars and broad absorption line quasars.

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A Systematic Analysis of Stellar Populations in the Host Galaxies of Changing-look AGNs

Cited by 9 publications

References 132 publications

Steep Balmer Decrement in Weak AGNs May Not Be Caused by Dust Extinction: Clues from Low-luminosity AGNs and Changing-look AGNs

Steep Balmer Decrement in Weak AGNs May Not Be Caused by Dust Extinction: Clues from Low-luminosity AGNs and Changing-look AGNs

Velocity Offset Between Emission and Absorption Lines Might Be an Effective Indicator of a Dual Core System

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Quasar Survey: Quasar Properties from Data Releases 6 to 9

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