Understanding Broad Mg ii Variability in Quasars with Photoionization: Implications for Reverberation Mapping and Changing-look Quasars

Guo, Hengxiao; Shen, Yue; He, Zhicheng; Wang, Tinggui; Liu, Xin; Wang, Shu; Yang, Qian; Kong, Meiying; Sheng, Zhenfeng

doi:10.3847/1538-4357/ab5db0

Cited by 58 publications

(72 citation statements)

References 70 publications

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“…The difference from object to object will be a combination of intrinsic differences between the objects, and an artefact of the cadence of observations. The latter is caused by the fact that we only have two snapshots of the full line response, which means we will observe the line in different stages of its response for every target (in agreement with the evolutionary 'sequence' proposed in Guo et al (2020)). The metrics of correlation and responsivity for the two samples are summarised in Table 6.…”

Section: Flux Normalisationssupporting

confidence: 83%

“…Although this is in agreement with RM studies, the research presented here indicates that the Mg II behaviour is more complex than a suppressed response compared to the Balmer lines. The observed pattern of behaviour agrees with the CL 'sequence' presented in Guo et al (2020), although we would argue that the marked difference in possible responses among the AGN population suggests that the response is not determined by changes in the luminosity alone. Rather, a range of conditions in the BLR likely conspire to create a specific responsivity (Homan et al 2020).…”

Section: Full Populationsupporting

confidence: 82%

“…Interestingly, Roig et al (2014) found a class of quasars characterised by a strongly suppressed broad Hα and Hβ emission and a very prominent Mg II line, without signs of reddening. This population fits well in the evolutionary sequence presented in Guo et al (2020): Based on a photoionisation model Guo et al (2020) find that Mg II responds consistently to continuum changes, but at a much diminished level compared to the Balmer lines.…”

Section: Introductionsupporting

confidence: 72%

“…This region largely overlaps with the parts of the cloud where H is neutral. As the collisional excitation of Mg II depends on the the electron density (n e ) and the temperature (Guo et al 2020), the formation region of the 2798Å line is likely associated with the transition region between the HII and HI regions of BLR clouds, where Hβ is also formed (MacAlpine 1972;Netzer 1980;Collin-Souffrin et al 1986;Krolik 1999). If the line forming regions of Hβ and Mg II are so intimately linked, a very different geometry for the two appears less probable.…”

Section: Full Populationmentioning

confidence: 99%

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Behaviour of the Mg ii 2798 Å line over the full range of AGN variability

Homan

MacLeod

Lawrence

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We investigate the responsiveness of the 2798 Å Mg ii broad emission line in active galactic nuclei (AGNs) on time-scales of several years. Our study is based on a sample of extremely variable AGNs as well as a broad population sample. The observed response of the line in previous studies has been mixed. By focusing on extreme variability (|Δg| > 1), we find that Mg ii clearly does respond to the continuum. However, the degree of responsiveness varies strikingly from one object to another: We see cases of Mg ii changing by as much as the continuum, more than the continuum, or very little at all. In 74 per cent of the highly variable sample, the behaviour of Mg ii corresponds with that of H β, with 30 per cent of the objects showing large variations in both lines. We do not detect any change in the line width that would correspond to broad-line region ‘breathing’, in accordance with results from the literature. Some of the objects in our highly variable sample show a clear asymmetry in the Mg ii profile. This skewness can be both to the blue and the red of the line centre. Results from our broad population sample show that highly variable quasars have lower Eddington ratios. This result holds for the variability of the continuum, but the correlation is significantly reduced for the variability of the Mg ii line. For the first time, we present an overview of the value of the intrinsic Baldwin effect for Mg ii in a large sample.

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Section: Flux Normalisationssupporting

confidence: 83%

Section: Full Populationsupporting

confidence: 82%

Section: Introductionsupporting

confidence: 72%

Section: Full Populationmentioning

confidence: 99%

See 2 more Smart Citations

Behaviour of the Mg ii 2798 Å line over the full range of AGN variability

Homan

MacLeod

Lawrence

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Shen 2013) and is believed to be more reliable than Mg II as a virial mass estimator (e.g. Guo et al 2020b) and OzDES spectrum is incomplete for the H β- [O III] region.…”

Section: Black Hole Mass Estimationmentioning

confidence: 99%

Dark Energy Survey identification of a low-mass active galactic nucleus at redshift 0.823 from optical variability

Guo¹,

Burke²,

Liu³

et al. 2020

Monthly Notices of the Royal Astronomical Society

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ABSTRACT We report the identification of a low-mass active galactic nucleus (AGN), DES J0218−0430, in a redshift z = 0.823 galaxy in the Dark Energy Survey (DES) Supernova field. We select DES J0218−0430 as an AGN candidate by characterizing its long-term optical variability alone based on DES optical broad-band light curves spanning over 6 yr. An archival optical spectrum from the fourth phase of the Sloan Digital Sky Survey shows both broad Mg ii and broad H β lines, confirming its nature as a broad-line AGN. Archival XMM–Newton X-ray observations suggest an intrinsic hard X-ray luminosity of $L_{{\rm 2-12\, keV}}\approx 7.6\pm 0.4\times 10^{43}$ erg s−1, which exceeds those of the most X-ray luminous starburst galaxies, in support of an AGN driving the optical variability. Based on the broad H β from SDSS spectrum, we estimate a virial black hole (BH) mass of M• ≈ 106.43–106.72 M⊙ (with the error denoting the systematic uncertainty from different calibrations), consistent with the estimation from OzDES, making it the lowest mass AGN with redshift > 0.4 detected in optical. We estimate the host galaxy stellar mass to be M* ≈ 1010.5 ± 0.3 M⊙ based on modelling the multiwavelength spectral energy distribution. DES J0218−0430 extends the M•–M* relation observed in luminous AGNs at z ∼ 1 to masses lower than being probed by previous work. Our work demonstrates the feasibility of using optical variability to identify low-mass AGNs at higher redshift in deeper synoptic surveys with direct implications for the upcoming Legacy Survey of Space and Time at Vera C. Rubin Observatory.

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Changing-look active galactic nuclei

Ricci,

Trakhtenbrot

2023

Nat Astron

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Understanding Broad Mg ii Variability in Quasars with Photoionization: Implications for Reverberation Mapping and Changing-look Quasars

Cited by 58 publications

References 70 publications

Behaviour of the Mg ii 2798 Å line over the full range of AGN variability

Behaviour of the Mg ii 2798 Å line over the full range of AGN variability

Dark Energy Survey identification of a low-mass active galactic nucleus at redshift 0.823 from optical variability

Changing-look active galactic nuclei

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